Hydrological Processes

Impacts of nutrient management and decrease in paddy field area on groundwater nitrate concentration: a case study at the Nasunogahara alluvial fan, Tochigi Prefecture, Japan

Hiroaki Somura, Akira Goto, Hiroyuki Matsui, Elhassan Ali Musa — 2008-06-18T06:25:00Z

In order to help evaluate the trends in the NO3-N concentration in groundwater with a view to preventing further degradation in water quality in the future, a distributed groundwater quality model was constructed for the Nasunogahara basin. The best fit for the groundwater table elevations by the flow component of the model was achieved with average mean absolute errors (MAEs) of 0·92 m for the calibration period and 0·83 m for the validation period. Moreover, the best fit for the NO3-N concentration by the water quality component was achieved with average mean relative errors (MREs) of 29·8% for the calibration period and 30·3% for the validation period. After developing a robust model, various change scenarios were tested; specifically, the effects of effluent load control and a decrease in paddy field area on the NO3-N concentration in groundwater were predicted. The most intensively farmed area contributed about 40% of the total effluent load because of livestock farming in the basin. When the effluent load from this area was decreased by 50%, the average NO3-N concentrations at sites S1, S2 and S3 were reduced by about 15%; however, the average concentrations at S4 and S5 were reduced by only 1%. Furthermore, when the total effluent load from the concentrated livestock area was removed completely, the average groundwater NO3-N concentrations at S1, S2 and S3 were reduced by about 30% as compared with the original calculated results. In contrast, decreasing the area of the paddy fields in the basin did not greatly influence the groundwater NO3-N concentration. In the case of a 70% reduction in paddy field area, average NO3-N concentrations increased by about 7% at S1, S2 and S3. Copyright © 2008 John Wiley & Sons, Ltd.

Geomorphologic control on pollutant retardation at the groundwater-surface water interface

J.W.N. Smith, D.N. Lerner — 2008-06-17T05:34:00Z

The results of research on the pollutant retardation potential of permeable riverbed sediments in catchments with significant groundwater-surface water (GW-SW) interaction are presented. The fraction of organic carbon and cation exchange capacity of fluvial sediments in various geomorphologic environments have been quantified. Sediments in selected reaches of the rivers Tern and Leith (UK), from the underlying Permian sandstone aquifers, and from along the length of the rivers Severn and Eden into which the Tern and Leith discharge have been investigated. Statistical analyses show significant variation in the geochemistry and pollutant retardation potential of sediments from different geomorphologic features, and between upland and lowland rivers. The sorption potential of fine-grained sediments deposited in pools was greater than sand in runs and coarser deposits in riffles. Similarly, sediments in lowland rivers were found to have a greater retardation potential than those in upland rivers. There was generally greater retardation potential in fluvial sediments of all types than in the underlying aquifers, and in lowland rivers the fluvial sediment retardation potential greatly dominated that of the aquifer. The findings demonstrate the potential for pollutant retardation processes in riverbed sediments of sandstone catchments, and suggest that consideration of retardation processes at the groundwater-surface water interface should be included into environmental risk-assessment studies, in order to better assess and manage the effects of contaminated groundwater discharges to rivers, particularly in lowland catchments. Copyright © 2008 John Wiley & Sons, Ltd.

The effect of climate and land use change on flow duration in the Maryland Piedmont region

Mohamad I. Hejazi, Glenn E. Moglen — 2008-06-17T03:40:00Z

This paper describes the use of a continuous streamflow model to examine the effects of climate and land use change on flow duration in six urbanizing watersheds in the Maryland Piedmont region. The hydrologic model is coupled with an optimization routine to achieve an agreement between observed and simulated streamflow. Future predictions are made for three scenarios: future climate change, land use change, and jointly varying climate and land use. Future climate is modelled using precipitation and temperature predictions for the Canadian Climate Centre (CCC) and Hadley climate models. Results show that a significant increase in temperature under the CCC climate predictions produces a decreasing trend in low flows. A significant increasing trend in precipitation under the Hadley climate predictions produces an increasing trend in peak flows. Land use change by itself, as simulated by an additional 10% increase in imperviousness (from 20·5 to 30·5%), produces no significant changes in the simulated flow durations. However, coupling the effects of land use change with climate change leads to more significant decreasing trends in low flows under the CCC climate predictions and more significant increasing trends in peak flows under Hadley climate predictions than when climate change alone is employed. These findings indicate that combined land use and climate change can result in more significant hydrologic change than either driver acting alone. Copyright © 2008 John Wiley & Sons, Ltd.

Comparison of hydrodynamic models of different complexities to model floods with emergency storage areas

Chandranath Chatterjee, Saskia Förster, Axel Bronstert — 2008-06-16T05:32:00Z

A flood emergency storage area (polder) is used to reduce the flood peak in the main river and hence, protect downstream areas from being inundated. In this study, the effectiveness of a proposed flood emergency storage area at the middle Elbe River, Germany in reducing the flood peaks is investigated using hydrodynamic modelling. The flow to the polders is controlled by adjustable gates. The extreme flood event of August 2002 is used for the study. A fully hydrodynamic 1D model and a coupled 1D-2D model are applied to simulate the flooding and emptying processes in the polders and flow in the Elbe River. The results obtained from the 1D and 1D-2D models are compared with respect to the peak water level reductions in the Elbe River and flow processes in the polders during their filling and emptying. The computational time, storage space requirements and modelling effort for the two models are also compared. It is concluded that a 1D model may be used to study the water level and discharge reductions in the main river while a 1D-2D model may be used when the study of flow dynamics in the polder is of particular interest. Further, a detailed sensitivity analysis of the 1D and 1D-2D models is carried out with respect to Manning's n values, DEMs of different resolutions, number of cross-sections used and the gate opening time as well as gate opening/closing duration. Copyright © 2008 John Wiley & Sons, Ltd.

Smoothed minima baseflow separation tool for perennial and intermittent streams

Hafzullah Aksoy, Necati Erdem Unal, Ali Osman Pektas — 2008-06-13T12:04:00Z

The United Kingdom Institute of Hydrology (UKIH) smoothed minima baseflow separation method originally developed for the daily flow data of perennial streams and adopted for intermittent streams is presented. The adopted method (AdUKIH) is the generalized version of the UKIH and hence applicable not only to intermittent streams but also to perennial streams. The AdUKIH method is applied on three daily streamflow gauging stations from the European part of Turkey, the Thrace region. The AdUKIH enables one to change the parameter 0·9 in the UKIH method and also introduces different block sizes, which is limited to five days in the original UKIH method. The AdUKIH method is considered a useful tool in helping practitioners and researchers to separate continuous baseflow from the daily flow in perennial and intermittent streams. Copyright © 2008 John Wiley & Sons, Ltd.

Distribution of snow accumulation on the Svartisen ice cap, Norway, assessed by a model of orographic precipitation

T. V. Schuler, P. Crochet, R. Hock, M. Jackson, I. Barstad, T. Jóhannesson — 2008-06-13T12:00:00Z

We apply a linear model of orographic precipitation (LT model) to estimate snow accumulation on the western Svartisen ice cap (220 km2) in northern Norway. This model combines 3D airflow dynamics with simple parameterizations of cloud physics. The model is forced by large-scale atmospheric input variables taken from the ECMWF Re-analysis (ERA-40) of the European Center for Medium Range Weather Forecast (ECMWF), and the model parameters are kept constant for the entire simulation period, after optimization. The domain covers a 120 × 125 km area surrounding the ice cap. The model is run using a 1-km resolution digital elevation model, and 6-h time steps over the period from 1958 to 2002. Precipitation data from surrounding meteorological stations and winter glacier mass balance measurements on several glaciers within the region are used to evaluate the model results. Precipitation obtained from the LT model agrees well with observations from precipitation gauges and there is also fair agreement between model results and specific winter mass balance observations on the ice cap if these are corrected for winter rain. The LT model reproduces well the spatial pattern of winter accumulation across the ice cap as well as the area-averaged winter mass balances of several other glaciers in the region. This indicates that it is a useful tool in providing high-resolution, deterministic estimates of precipitation in complex terrain as required for distributed hydrological and/or glacier mass balance modelling of unmeasured areas. Copyright © 2008 John Wiley & Sons, Ltd.

Mining lakes as groundwater-dominated hydrological systems: assessment of the water balance of Mining Lake Plessa 117 (Lusatia, Germany) using stable isotopes

Hilmar Hofmann, Kay Knöller, Dieter Lessmann — 2008-06-13T11:56:00Z

In the present study, the stable isotopes [delta]18O and [delta]2H were used for assessment of the water balance in a heterogeneously structured catchment area in the Lusatian Lignite Mining District, in particular, for estimation of the annual groundwater inflow and outflow (IGW and OGW) of Mining Lake Plessa 117. The application of stable isotopes was possible since the water exchange in the catchment area had reached steady-state conditions after the abandonment of mining activities in 1968 and the filling of the voids and aquifers by re-rising groundwater in the years thereafter. Diverging slopes of the Evaporation Line and the Global Meteoric Water Line manifested as evaporation from the lake catchment area. The calculated isotope water balance was compared with the commonly used surface water balance, which is unable to differentiate between IGW and OGW, and with a local groundwater model. The groundwater model calculated an IGW of about 811 000 m3 yr-1 and an OGW close to zero, whereas the isotope water balance showed fluxes of about 914 000 and 140 000 m3 yr-1, respectively. Considering the contribution of the groundwater inflow to the total annual input into the lake ([Delta]IT) and the mean residence time ([tau]), where the groundwater model and the isotope water balance calculated 42 and 47% for [Delta]IT and 4·3 and 3·9 years for [tau], respectively, it was shown that both water balance calculation methods led to comparable results despite the differences in IGW and OGW. Copyright © 2008 John Wiley & Sons, Ltd.

Frontiers in riparian zone research in the 21st century

C. J. Allan, P. Vidon, R. Lowrance — 2008-06-10T03:43:00Z

No Abstract.

Temporal monitoring of water level changes in Seyfe Lake using remote sensing

Selcuk Reis, Haci Murat Yilmaz — 2008-06-04T09:44:00Z

The Earth's water resources are endangered by inconsiderate use, pollution and lack of conservation measures. Temporal monitoring is necessary for the conservation and usage planning of water resources and to make informed decisions. Seyfe Lake and its environs in Turkey is one of the most important water basins in the world, because it is a node on bird migration paths between Europe, Asia and Africa. For this reason, the International Council of Bird Preservation (ICBP) has registered 27 of the bird species living at Seyfe Lake on the conservation list. In this work, the temporal changes in the water surface area of Seyfe Lake and its environs, which are important for ecological, historical and tourism reasons, are investigated. The change of water surface in the lake is examined over a 26 year period using satellite images taken between 1975 and 2001. Landsat images from years 1975, 1987 and 2001 are used. The change is tracked from the images using an unsupervised classification method. A decrease of slightly more than 33% was observed in the water surface area this 26 year period. The temporal change indicated by the images was compared with the related meteorological data between 1975 and 2001. Over this time period, climate conditions (rainfall, temperature and evaporation) in the study area have been changed by approximately 21%. These changes could have affected the Lake surface area, but so also could external human interference around the Lake. Copyright © 2008 John Wiley & Sons, Ltd.

Analytical power series solutions to the two-dimensional advection-dispersion equation with distance-dependent dispersivities

Jui-Sheng Chen, Chuen-Fa Ni, Ching-Ping Liang — 2008-05-28T08:57:00Z

As is frequently cited, dispersivity increases with solute travel distance in the subsurface. This behaviour has been attributed to the inherent spatial variation of the pore water velocity in geological porous media. Analytically solving the advection-dispersion equation with distance-dependent dispersivity is extremely difficult because the governing equation coefficients are dependent upon the distance variable. This study presents an analytical technique to solve a two-dimensional (2D) advection-dispersion equation with linear distance-dependent longitudinal and transverse dispersivities for describing solute transport in a uniform flow field. The analytical approach is developed by applying the extended power series method coupled with the Laplace and finite Fourier cosine transforms. The developed solution is then compared to the corresponding numerical solution to assess its accuracy and robustness. The results demonstrate that the breakthrough curves at different spatial locations obtained from the power series solution show good agreement with those obtained from the numerical solution. However, owing to the limited numerical operation for large values of the power series functions, the developed analytical solution can only be numerically evaluated when the values of longitudinal dispersivity/distance ratio eL exceed 0·075. Moreover, breakthrough curves obtained from the distance-dependent solution are compared with those from the constant dispersivity solution to investigate the relationship between the transport parameters. Our numerical experiments demonstrate that a previously derived relationship is invalid for large eL values. The analytical power series solution derived in this study is efficient and can be a useful tool for future studies in the field of 2D and distance-dependent dispersive transport. Copyright © 2008 John Wiley & Sons, Ltd.

Monotonic trend and abrupt changes for major climate variables in the headwater catchment of the Yellow River basin

F. F. Zhao, Z. X. Xu, J. X. Huang, J. Y. Li — 2008-06-04T09:35:00Z

On the basis of the mean air temperature, precipitation, sunshine duration and pan evaporation at 23 meteorological stations in the headwater catchment of the Yellow River basin from 1960 to 2001, the long-term monotonic trend and abrupt changes for major climate variables have been investigated. The plausible monotonic trend of annual climatic time series are detected using a non-parametric method. The abrupt changes have been investigated in terms of a 5 year moving averaged annual series, using the moving t-test (MTT) method, Yamamoto method and Mann-Kendall method. The results showed that the annual air temperature has increased by 0·80 °C in the headwater catchment of the Yellow River basin during the past 42 years. One obvious cold period and one warm period were detected. The warmest centre was located in the northern part of the basin. The long-term trend for annual precipitation was not significant during the same period, but a dry tendency was detected. According to the Kendall slope values, the declining centre for annual precipitation was located in the eastern part and the centre of the study area. The long-term monotonic trend for annual sunshine duration and pan evaporation were negative. The average Kendall slopes are - 29·96 h/10 yr and - 39·63 mm/10 yr, respectively. The tests for abrupt changes using MTT and Yamamoto methods show similar results. Abrupt changes occurred in the mid 1980s for temperature, in the late 1980s for precipitation and in the early 1980s for sunshine duration and pan evaporation. It can be seen that the abrupt changes really happened in the 1980s for the climate variables. Different results are shown using the Mann-Kendall method. Both the abrupt changes of temperature and precipitation took place in the early 1990s, and that of pan evaporation occurred in the 1960s. The only abrupt change in sunshine duration happened during the similar period (in the 1980s) with the results detected by the MTT and Yamamoto methods. The abrupt changes which occurred in the 1990s and 1960s are not detectable using the MTT and Yamamoto methods because of the data limitation. However, the results tested by the MTT and Yamamoto methods exhibited great consistency. Some of the reasons may be due to the similar principles for these two methods. Different methods testing the abrupt climatic changes have their own merits and limitations and should be compared based on their own assumption and applicable conditions when they are used. Copyright © 2008 John Wiley & Sons, Ltd.

Rain event properties in nature and in rainfall simulation experiments: a comparative review with recommendations for increasingly systematic study and reporting

David Dunkerley — 2008-06-04T09:32:00Z

In hydrology and geomorphology, less attention has been paid to rain event properties such as duration, mean and peak rain rate than to rain properties such as drop size or kinetic energy. A literature review shows a lack of correspondence between natural and simulated rain events. For example, 26 studies that report event statistics from substantial records of natural rain reveal a mean rain rate of just 3·47 mm h-1 (s.d. 2·38 mm h-1). In 17 comparable studies dealing with extreme rain rates including events in cyclonic, tropical convective, and typhoon conditions, a mean maximum rain rate (either hourly or mean event rain rate) of 86·3 mm h-1 (s.d. 57·7 mm h-1) is demonstrated. However, 49 studies using rainfall simulation involve a mean maximum rain rate of 103·1 mm h-1 (s.d. 81·3 mm h-1), often sustained for > 1 h, exceeding even than of extreme rain events, and nearly 30 times the mean rain rate in ordinary, non-exceptional, rain events. Thus rainfall simulation is often biased toward high rain rates, and many of the rates employed (in several instances exceeding 150 mm h-1) appear to have limited relevance to ordinary field conditions. Generally, simulations should resemble natural rain events in each study region. Attention is also drawn to the raindrop arrival rate at the surface. In natural rain, this is known to vary from < 100 m-2 s-1 to > 5000 m-2 s-1. Arrival rate may need to be added to the list of parameters that must be reproduced realistically in rainfall simulation studies. Copyright © 2008 John Wiley & Sons, Ltd.

Hydrologic history of the Mississippi and Lower Missouri Rivers based upon a refined specific-gauge approach

Abebe A. Jemberie, Nicholas Pinter, Jonathan W. F. Remo — 2008-05-28T12:40:00Z

A refined specific-gauge approach was developed to quantify changes over time in hydrological response on 3260 km of the Mississippi River system using long-term data observed at 67 hydrologic measurement stations. Of these stations, 49 were unrated (stage-only) stations, for which over 2 000 000 'synthetic discharges' were generated based on measured discharge values at nearby rated stations. The addition of these synthetic discharges nearly tripled the number of stations in the study area for which specific-gauge analysis could be performed. In order to maintain spatial homogeneity across such a broad study area, discharges were normalized to multiples of mean daily flow (MDF). Specific-gauge analysis calculates stage changes over time for invariant discharge conditions. Two discharges were analysed: low-flow and flood conditions at each station. In order to avoid the large errors associated with extrapolation of annual rating curves, a new 'enhanced interpolation' technique was developed that calculates continuous specific-stage time series, even for rare discharges. Thus enhanced, specific-gauge analysis is a useful reconnaissance tool for detecting geomorphic and hydrologic trends over time. Results show that on the Middle Mississippi River and Lower Missouri River, flood stages increased at all stations in spite of widespread incision of the river bed. On the Lower Mississippi River, both low-flow and flood stages decreased, mainly the result of artificial meander cutoffs in the late 1920s and 1930s, except downstream of Natchez, MS, where net aggradation was observed. On the Upper Mississippi River, the specific-gauge trends were dominated by emplacement of navigational dams and impoundment of slackwater pools. On all four river reaches, these results document hydrologic responses to the different engineering toolkits used on the different portions of the Mississippi River system during the past 75-150 years. Copyright © 2008 John Wiley & Sons, Ltd.

A coupled vertically integrated model to describe lateral exchanges between surface and subsurface in large alluvial floodplains with a fully penetrating river

D. Peyrard, S. Sauvage, P. Vervier, J. M. Sanchez-Perez, M. Quintard — 2008-06-04T09:18:00Z

This paper presents a vertically averaged model for studying water and solute exchanges between a large river and its adjacent alluvial aquifer. The hydraulic model couples horizontal 2D Saint Venant equations for river flow and a 2D Dupuit equation for aquifer flow. The dynamic coupling between river and aquifer is provided by continuity of fluxes and water level elevation between the two domains. Equations are solved simultaneously by linking the two hydrological system matrices in a single global matrix in order to ensure the continuity conditions between river and aquifer and to accurately model two-way coupling between these two domains. The model is applied to a large reach (about 36 km2) of the Garonne River (south-western France) and its floodplain, including an instrumented site in a meander. Simulated hydraulic heads are compared with experimental measurements on the Garonne River and aquifer in the floodplain. Model verification includes comparisons for one point sampling date (27 piezometers, 30 March 2000) and for hydraulic heads variations measured continuously over 5 months (5 piezometers, 1 January to 1 June 2000). The model accurately reproduces the strong hydraulic connections between the Garonne River and its aquifer, which are confirmed by the simultaneous variation of the water level in the river and in piezometers located near the river bank. The simulations also confirmed that the model is able to reproduce groundwater flow dynamics during flood events. Given these results, the hydraulic model was coupled with a solute-transport component, based on advection-dispersion equations, to investigate the theoretical dynamics of a conservative tracer over 5 years throughout the 36 km2 reach studied. Meanders were shown to favour exchanges between river and aquifer, and although the tracer was diluted in the river, the contamination moved downstream from the injection plots and affected both river banks. Copyright © 2008 John Wiley & Sons, Ltd.

Influence of species and rain event characteristics on stemflow volume in a temperate mixed oak-beech stand

Frédéric André, Mathieu Jonard, Quentin Ponette — 2008-06-04T09:23:00Z

This study aimed at analysing the effects of biological and meteorological factors on stemflow generation in a temperate mixed oak (Quercus petraea Liebl.) and beech (Fagus sylvatica L.) stand. A statistical model was developed to predict single-event individual stemflow volume from trunk circumference and rainfall depth allowing mechanistic stemflow parameters to be deduced from the model, namely stemflow rates (SFrate), storage of water on tree organs (St) and rainfall thresholds for stemflow (RFmin). SFrate and St increased with increasing trunk circumference while RFmin was not significantly influenced by tree size. RFmin and, for a given tree size, St were higher for oak than for beech, and inversely for SFrate. For each species, RFmin was higher for the leaved season than for the leafless period, while the opposite was found for SFrate, and St was not significantly affected by the season. Increasing wind speed during rain increased SFrate, lowered RFmin and did not influence St. In contrast, St and RFmin tended, respectively, to decrease and to increase with increasing values of the ratio between the cumulated potential evaporation during the dry period preceding the rain event and the volume of the preceding rainfall (Eva pADP/Rprevious). Stemflow volume, which results from the combined effects of the previous parameters, was higher for beech than for oak and also higher during the leafless period than during the leaved period; these differences were large for the smallest events but decreased rapidly as rainfall depth increased. In addition, an enhancing and a depressing effect on stemflow volume were shown for the average wind speed during rain and for the ratio Eva pADP/Rprevious, respectively. Copyright © 2008 John Wiley & Sons, Ltd.

Short-term variability in isotopic composition of precipitation: A case study from the Midwestern United States

M. Z. Iqbal — 2008-06-03T12:41:00Z

Oxygen and deuterium isotopes in precipitation were analysed to define local isotopic trends in Iowa, US. The area is far inland from an oceanic source and the observed averages of [delta]18O and [delta] D are - 6·43[permil] and - 41·35[permil] for Ames, - 7·53[permil] and - 51·33[permil] for Cedar Falls, and - 6·01[permil] and - 38·19[permil] for Iowa City, respectively. Although these data generally follow global trends, they are different when compared to a semi-arid mid-continental location in North Platt, Nebraska. The local meteoric water lines of Iowa are [delta] D = 7·68 [delta]18O + 8·0 for Ames, [delta] D = 7·62 [delta]18O + 6·07 for Cedar Falls, and [delta] D = 7·78 [delta]18O + 8·61 for Iowa City. The current Iowa study compares well with a study conducted in Ames, Iowa, 10 years earlier. The differences between Iowa and Nebraska studies are attributed to a variable climate across the northern Great Plains ranging from sub-humid in the east to semi-arid in the west. Iowa being further east in the region is more strongly influenced by a moist sub-humid to humid climate fed by the tropical air stream from the Gulf of Mexico. The average d-excess values are 10·06[permil] for Ames, 8·92[permil] for Cedar Falls and 9·92[permil] for Iowa City. Eighty seven percent of the samples are within the global d-excess range of 0[permil] and 20[permil]. The results are similar to previous studies, including those by National Atmospheric Deposition Programs and International Atomic Energy Agency. It appears that the impact of recycled water or secondary evaporation on [delta]18O values of area precipitation is minimal. Copyright © 2008 John Wiley & Sons, Ltd.

Fast segmentation algorithms for long hydrometeorological time series

Hafzullah Aksoy, Abdullah Gedikli, N. Erdem Unal, Athanasios Kehagias — 2008-06-03T12:38:00Z

A time series with natural or artificially created inhomogeneities can be segmented into parts with different statistical characteristics. In this study, three algorithms are presented for time series segmentation; the first is based on dynamic programming and the second and the third - the latter being an improved version of the former - are based on the branch-and-bound approach. The algorithms divide the time series into segments using the first order statistical moment (average). Tested on real world time series of several hundred or even over a thousand terms the algorithms perform segmentation satisfactorily and fast. Copyright © 2008 John Wiley & Sons, Ltd.

East Greenland freshwater runoff to the Greenland-Iceland-Norwegian Seas 1999-2004 and 2071-2100

Sebastian H. Mernild, Glen E. Liston, Bent Hasholt — 2008-05-06T12:20:00Z

In this paper, we quantify the terrestrial flux of freshwater runoff from East Greenland to the Greenland-Iceland-Norwegian (GIN) Seas for the periods 1999-2004 and 2071-2100. Our analysis includes separate calculations of runoff from the Greenland Ice Sheet (GrIS) and the land strip area between the GrIS and the ocean. This study is based on validation and calibration of SnowModel with in situ data from the only two long-term permanent automatic meteorological and hydrometric monitoring catchments in East Greenland: the Mittivakkat Glacier catchment (65°N) in SE Greenland, and the Zackenberg Glacier catchment (74°N) in NE Greenland. SnowModel was then used to estimate runoff from all of East Greenland to the ocean. Modelled glacier recession in both catchments for the period 1999-2004 was in accordance with observations, and dominates the annual catchment runoff by 30-90%. Average runoff from Mittivakkat, [sim]3·7 × 10-2 km3 y-1, and Zackenberg, [sim]21·9 × 10-2 km3 y-1, was dominated by the percentage of catchment glacier cover. Modelled East Greenland freshwater input to the North Atlantic Ocean was [sim]440 km3 y-1 (1999-2004), dominated by contributions of [sim]40% from the land strip area and [sim]60% from the GrIS. East Greenland runoff contributes [sim]10% of the total annual freshwater export from the Arctic Ocean to the Greenland Sea. The future (2071-2100) climate impact assessment based on the Intergovernmental Panel on Climate Change (IPCC) A2 and B2 scenarios indicates an increase of mean annual East Greenland air temperature by 2·7 °C from today's values. For 2071-2100, the mean annual freshwater input to the North Atlantic Ocean is modelled to be [sim]650 km3 y-1: [sim]30% from the land strip area and [sim]70% from the GrIS. This is an increase of approximately [sim]50% from today's values. The freshwater runoff from the GrIS is more than double from today's values, based largely on increasing air temperature rather than from changes in net precipitation. Copyright © 2008 John Wiley & Sons, Ltd.

A comparison of three methods for determining vineyard evapotranspiration in the arid desert regions of northwest China

Sien Li, Shaozhong Kang, Lu Zhang, Fusheng Li, Zhilin Zhu, Baozhong Zhang — 2008-06-03T12:35:00Z

Accurate measurement and estimation of crop evapotranspiration (ET) plays an important role in understanding field soil water cycle and managing water-saving irrigation in the arid regions. This study compares three methods for estimating ET: field Water Balance (WB), Eddy Covariance (EC) and Bowen Ratio-Energy Balance (BREB). The experiment was conducted in a vineyard in the arid desert regions of northwest China. Results indicate that the three methods provided similar estimate of total ET. Compared to total ET measured by WB (ETWB) during the whole growing stage, total ET estimated by EC (ETEC) was 1·57% lower, and total ET estimated by BREB (ETBREB) was 5·19% higher. Variations of ETEC and ETBREB are similar at hourly or daily timescale, but the values are slightly different. At sunrise or sunset, ETBREB increases or decreases more rapidly than ETEC. The difference between ETBREB and ETEC is linearly related to the residual of the energy balance for EC and the two methods yielded close estimates when the residual was small. This study showed that the three methods provided accurate estimates of ET at daily and seasonal timescales and the methods can be used to estimate ET from vineyards in arid environments. Copyright © 2008 John Wiley & Sons, Ltd.

Spatial variation of isotope composition in precipitation in a tropical environment: a case study from the Deduru Oya river basin, Sri Lanka

H.A.H. Jayasena, Rohana Chandrajith, C.B. Dissanayake — 2008-06-03T12:33:00Z

The stable isotope composition (18O and 2H) in the tropical precipitation collected from 18 locations throughout the Deduru Oya river basin in Sri Lanka, has been studied during August and September 2001, in order to characterize the isotopic composition of precipitation in the dry and intermediate climatic zones of Sri Lanka. The isotope compositions are described with respect to the distance from the coast and the altitude. The analyses show that [delta]18O vary from - 5·11 to 1·39[permil] and [delta]D vary from - 35·71 to 12·55[permil]. The d-excess values range from - 0·65 to 13·17 with an average value of [sim]7. Regression for the [delta]18O - [delta]D is y = 6·8x + 4·9 (R2 = 0·9) which is compatible with the precipitation in other tropical regions. The lower slope in the regression line and the lower d-excess value indicate high temperature events which were possibly aided by concentration through successive evaporation within the atmosphere. The spatial variation of isotope composition indicates two different cloud contributions for the rain events, of which one may be linked to the Indian Ocean contribution and the other to the high altitude condensation. Copyright © 2008 John Wiley & Sons, Ltd.

Recent studies on surface water-groundwater relationships at hydro-projects in India using environmental isotopes

U. Saravana Kumar, Suman Sharma, S.V. Navada — 2008-06-03T12:31:00Z

Environmental isotopes (2H or D, 18O, 3H), along with geology, hydrochemistry and in situ physicochemical parameters (EC, T, DO, pH) were employed to study surface water (reservoir, lake)-groundwater (spring) relationships at (1) Nagewadi, a minor irrigation project in the State of Maharashtra, Western India; (2) Kanhirapuzha reservoir in the State of Kerala, Southern India and (3) Ghatghar Pumped Storage Hydroelectric Project in the State of Maharashtra, Western India for the purpose of understanding the seepage/leakage and its associated problems. The studies concluded that the springs found downstream of the Nagewadi project originate from the reservoir and not from the abutments or shallow aquifers. The Kanhirapuzha reservoir receives a substantial base-flow component compared to riverine inputs. The reason for the water-logging problem at a nearby downstream village during the non-summer periods is due to the change in the upstream groundwater flow direction under reservoir filling conditions and is not due to reservoir leakage. Most of the springs in the approach tunnel to the underground power house of the Ghatghar Project originate from the lower reservoir and not from the upper reservoir or the overburden rock matrix. The above case studies illustrate the diversity of environmental isotope applications in surface water (reservoir, lake)-groundwater (spring) relationships related to sustainability of hydro-projects. Copyright © 2008 John Wiley & Sons, Ltd.

Estimating parameters of groundwater recharge model in frequency domain: Karst springs Jadro and [Zcaron]rnovnica

Damir Juki[cacute], Vesna Deni[cacute]-Juki[cacute] — 2008-06-03T12:28:00Z

The spectral method is based on the assumption of exponential forms of autocorrelation functions of the input and output time series. The results of practical applications of the spectral method on several karst springs in Croatia show that this assumption cannot always be reliably applied to the time series of rainfall and spring discharge, especially if short time periods are analysed. For this reason, the method is modified. The scale factor between the transfer function of total rainfall and the transfer function of groundwater recharge is considered as an additional model parameter which is determined in the optimization procedure. In addition to the theoretical background, this paper also presents the results of application of the modified spectral method on the springs Jadro and [Zcaron]rnovnica located in the Dinaric karst area in Croatia. The parameters of groundwater recharge model are determined separately for both the springs and the obtained values are discussed and compared with the results of previous investigations. The values of the scale factors determined in the optimization procedure are compared to the values calculated using the theoretical equation. The comparison shows that the theoretical equation underestimates the optimal values of the scale factor. The underestimations are especially evident for periods of one year. Finally, the characteristics of rainfall-runoff relations of two springs are compared using the identified transfer functions and the results of simulations of the periodogram of observed discharge by the parametric periodogram. Copyright © 2008 John Wiley & Sons, Ltd.

Lateral flow thresholds for aspen forested hillslopes on the Western Boreal Plain, Alberta, Canada

T. E. Redding, K. J. Devito — 2008-05-28T12:54:00Z

To predict the long-term sustainability of water resources on the Boreal Plain region of northern Alberta, it is critical to understand when hillslopes generate runoff and connect with surface waters. The sub-humid climate (P [le] ET) and deep glacial sediments of this region result in large available soil storage capacity relative to moisture surpluses or deficits, leading to threshold-dependent rainfall-runoff relationships. Rainfall simulation experiments were conducted using large magnitude and high intensity applications to examine the thresholds in precipitation and soil moisture that are necessary to generate lateral flow from hillslope runoff plots representative of Luvisolic soils and an aspen canopy. Two adjacent plots (areas of 2·95 and 3·4 m2) of contrasting antecedent moisture conditions were examined; one had tree root uptake excluded for two months to increase soil moisture content, while the second plot allowed tree uptake over the growing season resulting in drier soils. Vertical flow as drainage and soil moisture storage dominated the water balances of both plots. Greater lateral flow occurred from the plot with higher antecedent moisture content. Results indicate that a minimum of 15-20 mm of rainfall is required to generate lateral flow, and only after the soils have been wetted to a depth of 0·75 m (C-horizon). The depth and intensity of rainfall events that generated runoff > 1 mm have return periods of 25 years or greater and, when combined with the need for wet antecendent conditions, indicate that lateral flow generation on these hillslopes will occur infrequently. Copyright © 2008 John Wiley & Sons, Ltd.

Evaluating sulfur dynamics during storm events for three watersheds in the northeastern USA: a combined hydrological, chemical and isotopic approach

Myron J. Mitchell, Scott W. Bailey, James B. Shanley, Bernhard Mayer — 2008-05-28T12:45:00Z

Concerns related to climate change have resulted in an increasing interest in the importance of hydrological events such as droughts in affecting biogeochemical responses of watersheds. The effects of an unusually dry summer in 2002 had a marked impact on the biogeochemistry of three watersheds in the north-eastern USA. Chemical, isotopic and hydrological responses with particular emphasis on S dynamics were evaluated for Archer Creek (New York), Sleepers River (Vermont) and Cone Pond (New Hampshire) watersheds. From 1 August to 14 September 2002, all three watersheds had very low precipitation (48 to 69 mm) resulting in either very low or no discharge (mean 0·015, 0·15 and 0·000 mm day-1 for Archer Creek, Sleepers River and Cone Pond, respectively). From 15 September to 31 October 2002, there was a substantial increase in precipitation totals (212, 246 and 198 mm, respectively) with increased discharge. Archer Creek was characterized by a large range of SO42- concentrations (152 to 389 µeq L-1, mean = 273 µeq L-1) and also exhibited the greatest range in [delta]34S values of SO42- (-1·4 to 8·8 [permil] ). Sleepers River's SO42- concentrations ranged from 136 to 243 µeq L-1 (mean = 167 µeq L-1) and [delta]34S values of SO42- ranged from 4·0 to 9·0 [permil] . Cone Pond's SO42- concentrations (126-187 µeq L-1, mean = 154 µeq L-1) and [delta]34S values (2·4 to 4·3 [permil] ) had the smallest ranges of the three watersheds. The range and mean of [delta]18O-SO42- values for Archer Creek and Cone Pond were similar (3·0 to 8·9 [permil] , mean = 4·5 [permil] ; 3·9 to 6·3 [permil] , mean = 4·9 [permil] ; respectively) while [delta]18O-SO42- values for Sleepers River covered a larger range with a lower mean (1·2 to 10·0 [permil] , mean = 2·5). The difference in Sleepers River chemical and isotopic responses was attributed to weathering reactions contributing SO42-. For Archer Creek wetland areas containing previously reduced S compounds that were reoxidized to SO42- probably provided a substantial source of S. Cone Pond had limited internal S sources and less chemical or isotopic response to storms. Differences among the three watersheds in S biogeochemical responses during these storm events were attributed to differences in S mineral weathering contributions, hydrological pathways and landscape features. Further evaluations of differences and similarities in biogeochemical and hydrological responses among watersheds are needed to predict the impacts of climate change. Copyright © 2008 John Wiley & Sons, Ltd.

Modelling runoff from highly glacierized alpine drainage basins in a changing climate

Matthias Huss, Daniel Farinotti, Andreas Bauder, Martin Funk — 2008-05-28T12:49:00Z

The future runoff from three highly glacierized alpine catchments is assessed for the period 2007-2100 using a glacio-hydrological model including the change in glacier coverage. We apply scenarios for the seasonal change in temperature and precipitation derived from regional climate models. Glacier surface mass balance and runoff are calculated in daily time-steps using a distributed temperature-index melt and accumulation model. Model components account for changes in glacier extent and surface elevation, evaporation and runoff routing. The model is calibrated and validated using decadal ice volume changes derived from four digital elevation models (DEMs) between 1962 and 2006, and monthly runoff measured at a gauging station (1979-2006). Annual runoff from the drainage basins shows an initial increase which is due to the release of water from glacial storage. After some decades, depending on catchment characteristics and the applied climate change scenario, runoff stabilizes and then drops below the current level. In all climate projections, the glacier area shrinks dramatically. There is an increase in runoff during spring and early summer, whereas the runoff in July and August decreases significantly. This study highlights the impact of glaciers and their future changes on runoff from high alpine drainage basins. Copyright © 2008 John Wiley & Sons, Ltd.

Frequency analysis for predicting 1% annual maximum water levels along Florida coast, US

Sudong Xu, Wenrui Huang — 2008-05-28T12:35:00Z

In the Coastal Flood Insurance Study by the Federal Emergency Management Agency (FEMA, 2005), 1% annual maximum coastal water levels are used in coastal flood hazard mitigation and engineering design in coastal areas of USA. In this study, a frequency analysis method has been developed to provide more accurate predictions of 1% annual maximum water levels for the Florida coast waters. Using 82 and 94 years of annual maximum water level data at Pensacola and Fernandina, performances of traditional frequency analysis methods, including advanced method of Generalized Extreme Value distribution method, have been evaluated. Comparison with observations of annual maximum water levels with 83 and 95 years of return periods indicate that traditional methods are unable to provide satisfactory predictions of 1% annual maximum water levels to account for hurricane-induced extreme water levels. Based on the characteristics of annual maximum water level distribution of Pensacola and Fernandina stations, a new probability distribution method has been developed in this study. Comparison with observations indicates that the method presented in this study significantly improves the accuracy of predictions of 1% annual maximum water levels. For Fernandina station, predictions of extreme water level match well with the general trend of observations. With a correlation coefficient of 0·98, the error for the maximum observed extreme water level of 3·11 m (National Geodetic Vertical Datum) with 95 years of return period is 0·92%. For Pensacola station, the prediction error for the maximum observed extreme water level with a return period of 83 years is 5·5%, with a correlation value of 0·98. The frequency analysis has also been reasonably compared to the more costly Monte Carlo simulation method. Copyright © 2008 John Wiley & Sons, Ltd.

Hydrogeologic controls on streamflow sensitivity to climate variation

Anne Jefferson, Anne Nolin, Sarah Lewis, Christina Tague — 2008-06-16T05:05:00Z

Climate models project warmer temperatures for the north-west USA, which will result in reduced snowpacks and decreased summer streamflow. This paper examines how groundwater, snowmelt, and regional climate patterns control discharge at multiple time scales, using historical records from two watersheds with contrasting geological properties and drainage efficiencies. In the groundwater-dominated watershed, aquifer storage and the associated slow summer recession are responsible for sustaining discharge even when the seasonal or annual water balance is negative, while in the runoff-dominated watershed subsurface storage is exhausted every summer. There is a significant 1 year cross-correlation between precipitation and discharge in the groundwater-dominated watershed (r = 0·52), but climatic factors override geology in controlling the inter-annual variability of streamflow. Warmer winters and earlier snowmelt over the past 60 years have shifted the hydrograph, resulting in summer recessions lasting 17 days longer, August discharges declining 15%, and autumn minimum discharges declining 11%. The slow recession of groundwater-dominated streams makes them more sensitive than runoff-dominated streams to changes in snowmelt amount and timing. Copyright © 2008 John Wiley & Sons, Ltd.

Hydrological behaviour and modelling of a volcanic tropical cultivated catchment

Jean-Baptiste Charlier, Philippe Cattan, Roger Moussa, Marc Voltz — 2008-05-27T12:09:00Z

The hydrological behaviour of the cultivated Féfé catchment (17·8 ha) on the tropical volcanic island of Guadeloupe was studied to identify flow paths, to quantify water fluxes, and finally, to build a lumped model to simulate discharge and piezometer levels. The approach combined two steps, an experimental step and a modelling step, which covered two time scales, the annual and the storm event scale. The hydrological measurements were conducted over 2 years. The Féfé catchment is characterized by heavy rainfall (4229 mm year-1) on permeable Andosols; the results showed that underground flow paths involved two overlapping aquifers, and that the annual water balance in 2003 was shared among outflows of the deep aquifer (42%), evapotranspiration (31%), and streamflow (27%). On the event scale, the surface runoff coefficient ranges between 6·2% and 24·4% depending on antecedent dry or wet moisture conditions. Hortonian overland flow predominated over subsurface and saturation overland flow processes. Recharge of the shallow aquifer is mainly governed by a constant infiltration capacity of the Andosols with depth in the vadose zone. Outflows of this shallow aquifer were the baseflow of the main stream and the recharge of the deep aquifer. Volcanic deposits at Féfé promoted the underground flow path, and cultivated areas seemed to explain the high stormflow values relative to other tropical small catchments under rain forest. A conceptual lumped model integrating runoff, infiltration, evapotranspiration, and fluctuations of the two overlapping aquifers was developed. The model has six parameters and was calibrated and validated on the hydrograph at the outlet and on the two piezometers of the shallow and the deep aquifers. The results show fair to good agreement between measured and simulated variables, and consequently, the model was consistent with the main hydrological processes observed from experimental results in wet conditions. Copyright © 2008 John Wiley & Sons, Ltd.

An approach to catchment-scale groundwater nitrate risk assessment from diffuse agricultural sources: a case study in the Upper Bann, Northern Ireland

J. L. Wang, Y. S. Yang — 2008-06-03T12:24:00Z

DRASTIC has drawbacks in groundwater risk assessment that are important in guiding activities to prevention agricultural diffuse groundwater pollution. This paper presents an improved and GIS-based D-DRASTIC approach for groundwater nitrate risk assessment from diffuse agricultural sources based on DRASTIC. D-DRASTIC considers the risk concept, nitrate loading, pollutant transport with runoff, depth to water, net recharge, aquifer media, soil media, topography, impact of the vadose zone media, and the hydraulic conductivity of the aquifer. D-DRASTIC was developed within an ArcGIS environment and applied to the Upper Bann Catchment, Northern Ireland as a case study. D-DRASTIC shows that 'very high' and 'high' zones of groundwater nitrate risk occupy 5% and 11% of the case study area, respectively. When considering groundwater pollution sources and pathways, the results using D-DRASTIC are helpful in guiding the activities of groundwater pollution prevention at the catchment scale in the context of better implementation of the EU Water Framework Directive. Copyright © 2008 John Wiley & Sons, Ltd.

Estimation of suspended sediment sources using 137Cs and 210Pbex in unmanaged Japanese cypress plantation watersheds in southern Japan

2008-05-13T04:05:00Z

To analyse suspended sediment sources in unmanaged Japanese cypress plantation watersheds, field measurements and fingerprinting of the suspended sediment was conducted in the Shimanto River basin in southern Japan. For sediment fingerprinting, 137Cs and 210Pbex were detected by means of gamma-ray spectrometry in the surface soil of the forest floor, stream bank and truck trail and mobilized sediment by interrill erosion. The 137Cs and 210Pbex activities associated with the forest floor materials were considerably higher than those of the stream bank and truck trail. The 137Cs and 210Pbex activities associated with the suspended sediment were found to vary with the sampling period. Evidently, the suspended sediment can comprise materials generated from the forest floor by interrill erosion and those from the truck trail and/or stream bank. The multivariate sediment-mixing model using 137Cs and 210Pbex showed that the contribution of the forest floor varied periodically, ranging from 23-56% in the Hinoki 156 subwatershed and from 18-85% in the Hinoki 155 subwatershed. The difference in the average contribution of the forest floor between Hinoki 156 (46%) and Hinoki 155 (69%) may relate to the presence of truck trail networks in the watershed. The truck trail network can play roles of sediment source and pathway for sediment from forest floor to stream channel due to the concentrated overland flow on the truck trail during heavy rainfall events. These results indicate that the forest floor should be recognized as a major source of suspended sediment in unmanaged Japanese cypress plantation watersheds. Copyright © 2008 John Wiley & Sons, Ltd.

Effects of subsurface drainage tiles on streamflow in Iowa agricultural watersheds: Exploratory hydrograph analysis

Keith E. Schilling, Matthew Helmers — 2008-05-07T12:53:00Z

Flow from artificial subsurface (tile) drainage systems may be contributing to increasing baseflow in Midwestern rivers and increased losses of nitrate-nitrogen. Standard hydrograph analysis techniques were applied to model simulation output and field monitoring from tile-drained landscapes to explore how flow from drainage tiles affects stream baseflow and streamflow recession characteristics. DRAINMOD was used to simulate hydrologic response from drained (24 m tile spacing) and undrained agricultural systems. Hydrograph analysis was conducted using programs PART and RECESS. Field monitoring data were obtained from several monitoring sites in Iowa typical of heavily drained and less-drained regions. Results indicate that flow from tile drainage primarily affects the baseflow portion of a hydrograph, increasing annual baseflow in streams with seasonal increases primarily occurring in the late spring and early summer months. Master recession curves from tile-drained watersheds appear to be more linear than less-tiled watersheds although comparative results of the recession index k were inconsistent. Considering the magnitude of non-point source pollutant loads coming from tile-drained landscapes, it is critical that more in-depth research and analysis be done to assess the effects of tile drainage on watershed hydrology if water quality solutions are to be properly evaluated. Copyright © 2008 John Wiley & Sons, Ltd.

Model data selection using gamma test for daily solar radiation estimation

R. Remesan, M. A. Shamim, D. Han — 2008-05-07T12:50:00Z

Hydrological modelling is a complicated procedure and there are many tough questions facing all modellers: what input data should be used? how much data is required? and what model should be used? In this paper, the gamma test (GT) has been used for the first time in modelling one of the key hydrological components: solar radiation. The study aimed to resolve the questions about the relative importance of input variables and to determine the optimum number of data points required to construct a reliable smooth model. The proposed methodology has been studied through the estimation of daily solar radiation in the Brue Catchment, the UK. The relationship between input and output in the meteorological data sets was achieved through error variance estimation before the modelling using the GT. This work has demonstrated how the GT helps model development in nonlinear modelling techniques such as local linear regression (LLR) and artificial neural networks (ANN). It was found that the GT provided very useful information for input data selection and subsequent model development. The study has wider implications for various hydrological modelling practices and suggests further exploration of this technique for improving informed data and model selection, which has been a difficult field in hydrology in past decades. Copyright © 2008 John Wiley & Sons, Ltd.

Chemical and isotopic assessment in volcanic thermal waters: Cases of Ischia (Italy) and São Miguel (Azores, Portugal)

Ignacio Morell, Antonio Pulido-Bosch, Linda Daniele, José Virgilio Cruz — 2008-04-28T11:37:00Z

Isotopic fractionation of 10B/11B provides a sound tool for identifying hydrogeochemical processes in complex areas, owing to its ability to discriminate between various scenarios. In addition, the occurrence of boron as a minor element in areas of active volcanism allows its use in comparison with concentrations of other conservative or non-conservative ions. This allows the detection of water mixtures of diverse origin and temperature, deep or shallow, including fresh water, seawater and even brines. This tool was applied in studies of the volcanic islands of Ischia and São Miguel, across widely differing geographical and climatic contexts. Five groups of waters have been identified in Ischia Island: marine, transition, hot carbonated, cold carbonated and fresh waters. For São Miguel Island the identified groups are cold carbonic, hot carbonic, boiling and acidic boiling waters. Copyright © 2008 John Wiley & Sons, Ltd.

Using multiple-variable indicator kriging to assess groundwater quality for irrigation in the aquifers of the Choushui River alluvial fan

Cheng-Shin Jang, Shih-Kai Chen, Lin Ching-Chieh — 2008-04-28T11:15:00Z

This work attempted to locate clean and safe groundwater for irrigation use in the Choushui River alluvial fan. Multiple-variable indicator kriging (MVIK) was adopted to evaluate numerous hydrochemical parameters for a standard of water quality for irrigation in Taiwan. Many hydrochemical parameters in groundwater were distinguished into three main categories - salinity/sodium hazard, nitrogen hazard and heavy metal hazard. Safe and potential hazardous regions of groundwater for irrigation were delineated according to different probabilities estimated by MVIK. The probabilistic results of the classifications gave an opportunity to explore the spatial uncertainty of the hazards and helped government administrators establish a sound policy associated with the development and management of groundwater resources. Analysis of the results indicate that the central distal-fan and mid-fan aquifers are the best places to extract clean and safe groundwater for irrigation, and the deep aquifer (exceeding 200 m depth) has wider regions with clean and safe groundwater for irrigation than shallow aquifers. The northern and southern aquifers, with multiple hazards, limit groundwater use for irrigation. Although the proximal-fan aquifer is a zone of groundwater recharge, the high nitrogen content seriously affects the environment and is not suitable for irrigation use. Copyright © 2008 John Wiley & Sons, Ltd.

Assessment of annual high-water events for the Mackenzie River basin, Canada

Laurent P. de Rham, Terry D. Prowse, Spyros Beltaos, Martin P. Lacroix — 2008-04-02T11:40:00Z

River ice break-up is known to have important morphological, ecological and socio-economic effects on cold-regions river environments. One of the most persistent effects of the spring break-up period is the occurrence of high-water events. A return-period assessment of maximum annual nominal water depths occurring during the spring break-up and open-water season at 28 Water Survey of Canada hydrometric sites over the 1913-2002 time period in the Mackenzie River basin is presented. For the return periods assessed, 13 (14) stations are dominated by peak events occurring during the spring break-up (open-water) season. One location is determined to have a mixed signal. A regime classification is proposed to separate ice- and open-water dominated systems. As part of the regime classification procedure, specific characteristics of return-period patterns including alignment, and difference between the 2 and 10-year events are used to identify regime types. A dimensionless stage-discharge plot allows for a contrast of the relative magnitudes of flows required to generate maximum nominal water-depth events in the different regimes. At sites where discharge during the spring break-up is approximately one-quarter or greater than the magnitude of the peak annual discharge, nominal water depths can be expected to exceed those occurring during the peak annual discharge event. Several physical factors (location, basin area, stream order, gradient, river orientation, and climate) are considered to explain the differing regimes and discussed relative to the major sub-regions of the MRB. Copyright © 2008 John Wiley & Sons, Ltd and Her Majesty the Queen in right of Canada.

The influence of resolution and topographic uncertainty on melt modelling using hypsometric sub-grid parameterization

Felix Hebeler, Ross S. Purves — 2008-04-21T12:08:00Z

Modelling of physical processes such as ablation or runoff at continental or global scales provides a key challenge: a high degree of abstraction is required in order to minimize computational demands, while spatial and temporal variability of key processes, often at the sub-scale level, need to be adequately captured and reproduced within a lower resolution model. For some approaches, such as temperature index models, downscaling to lower resolutions is straightforward. However a key issue when using these downscaled models is to assess the impact of scaling on model behaviour and results, including the associated uncertainties. We assess the impact of scaling on both a simple and an enhanced temperature index melt model from 100 m to 1, 5 and 10 km resolutions. Different sub-grid parameterization approaches are applied to both models across all resolutions and tested for their suitability against high-resolution reference data, with the aim of developing a robust, scalable and computationally undemanding parameterization. Results show patterns of over- and underestimation of potential melt rates for both models, with clear dependencies on scale, terrain roughness and variations of temperature thresholds, among other quantities. The sub-grid parameterizations tested in this article are found to effectively compensate these effects at little additional computational cost. Copyright © 2008 John Wiley & Sons, Ltd.

Effects of prescribed burnings on soil hydrological parameters

T. Vadilonga, X. Úbeda, P. F. Germann, M. Lorca — 2008-04-21T10:58:00Z

Prescribed burning is a forest management tool to reduce forest fire hazards. It is largely applied in the USA and is gaining importance worldwide, particularly in Europe. However, its effects on soils still have to be better understood. This study analyses the effects of two types of prescribed burnings (i.e. low and high burn severities of up to 200 °C and at or above 400 °C) on soil hydrophobicity, infiltration, and water storage capacity of top soils. Prescribed burnings were performed on four different plots in southern and western Catalonia, Spain. Soil samples were collected before and after burning to assess water repellency with the water drop penetration time (WDPT). Three rainfall simulations before burning and three after burning were executed on areas of 1 m2, and soil water contents at four to five depths were measured every 4 min during and after rainfall simulations using time domain reflectometry equipment (TDR). Following burning at both severities, water storage capacity of the top soil decreased between 1·7 and 5·4%vol on all four plots. No significant changes in volume flux density and velocity of the wetting fronts were discernible. Water drop penetration times increased moderately at the soil surface of the plots that were exposed to the high burn severity, and decreased slightly when burn severity was low. On two of the four plots the presence of partially moist organic litter prevented the underlying soil from excessive heating. Changes in hydrophobicity and water storage capacity of the top soil did not affect infiltration. Copyright © 2008 John Wiley & Sons, Ltd.

High frequency stream bed mobility of a low-gradient agricultural stream with implications on the hyporheic zone

Eric W. Peterson, Timothy B. Sickbert, Suzanna L. Moore — 2008-04-21T10:38:00Z

Little Kickapoo Creek (LKC), a low-gradient stream, mobilizes its streambed-fundamentally altering its near-surface hyporheic zone-more frequently than do higher-gradient mountain and karst streams. LKC streambed mobility was assessed through streambed surveys, sediment sampling, and theoretical calculations comparing basal shear stress ([tau]b) with critical shear stress ([tau]c). Baseflow [tau]b is capable of entraining a d50 particle; bankfull flow could entrain a 51·2 mm particle. No particle that large occurs in the top 30 cm of the substrate, suggesting that the top 30 cm of the substrate is mobilized and redistributed during bankfull events. Bankfull events occur on average every 7·6 months; flows capable of entraining d50 and d85 particles occur on average every 0·85 and 2·1 months, respectively. Streambed surveys verify streambed mobility at conditions below bankfull. While higher gradient streams have higher potential energy than LKC, they achieve streambed-mobilization thresholds less frequently. Heterogeneous sediment redistribution creates an environment where substrate hydraulic conductivity (K) varies over four orders of magnitude. The frequency and magnitude of the substrate entrainment has implications on hyporheic zone function in fluid, solute and thermal transport models, interpretations of hyporheic zone stability, and understanding of LKC's aquatic ecosystem. Copyright © 2008 John Wiley & Sons, Ltd.

Estimation of peak flows from small watersheds on the Loess Plateau of China

Suhua Fu, Xin Wei, Guanghui Zhang — 2008-04-21T10:33:00Z

Peak flow rate from watersheds is an important criterion used to develop soil conservation plans and to design engineering projects. A peak flow rate equation used in the CREAMS model, with four parameters, can be employed to predict peak flow rate. The purpose of this study was to test and improve this equation of peak flow rate in CREAMS for use on the Loess Plateau of China. Data from 331 storms in 20 small watersheds were used to verify the the peak flow rate equation in CREAMS. The calculated flow rates using the CREAMS equation greatly underestimated the measured peak flows. The model efficiency was only 0·15. Nonlinear regression analysis was then performed to develop a new equation:which gave a model efficiency of 0·94. A second set of data, including 68 storms from four completely different watersheds, was used to test the new equation, with a resultant model efficiency of 0·90. The result has significant implications for improving the design of soil and water supporting practices, for assessing the soil and water resources, and for implementing conservation programmes. Copyright © 2008 John Wiley & Sons, Ltd.

Ten-year water table recovery after clearcutting and draining boreal forested wetlands of eastern Canada

Philippe Marcotte, Vincent Roy, André P. Plamondon, Isabelle Auger — 2008-04-02T12:10:00Z

In boreal forested wetlands, the observed increase in the water table level after clearcutting (watering-up) is often a threat to sustained ecosystem productivity. Hydrologic recovery refers to the processes by which a water table progressively drops back to its initial level after the cut. In eastern Canada, drainage is used operationally after clearcutting wet sites in order to lower the water table level and accelerate hydrologic recovery. The objective of this study was to evaluate the duration of the watering-up caused by timber harvesting and the extent to which drainage affected the water table recovery on five peatlands and three hydromorphic mineral sites located in the St. Lawrence Lowlands of Québec (Canada). The mixed wood stands studied are dominated by balsam fir (Abies balsamea (L.) Mill.), eastern white cedar (Thuja occidentalis L.), and red maple (Acer rubrum L). Results indicate that, 10 years after clearcutting, water table levels in undrained plots are still 5 to 7 cm higher than the pre-cut levels. The slight recovery in water table level plateaued after the third year. Rainfall interception by vegetation was also monitored, and after 10 years had reached nearly 50% of the pre-cut rate. The immediate water table drawdown following drainage mitigated watering-up within 40 m of a ditch. The persistent watering-up observed in this study should encourage using sylvicultural systems adapted to boreal forested wetlands in order to prevent productivity loss and stand conversion. Copyright © 2008 John Wiley & Sons, Ltd.

It goes both ways: measurements of simultaneous evapotranspiration and fog droplet deposition at a montane cloud forest

E. Beiderwieden, V. Wolff, Y.-J. Hsia, O. Klemm — 2008-04-02T12:02:00Z

Fluxes of latent heat, sensible heat, and water vapor, including turbulent deposition of fog droplets, were measured for two months in autumn 2005 within a subtropical montane cypress forest in Taiwan. The goal of the study was to determine whether significant evapotranspiration can occur during foggy conditions. Water vapor fluxes, QW, as determined with the Bowen Ratio method, were compared to those simultaneously measured with the eddy covariance method. The median Bowen Ratio was 1.06, and the median QW flux was 5 · 2 × 10-5 kg m-2 s-1. The vertical gradients of temperature and specific humidity over the forest, [Delta]T and [Delta]q, peaked around noon during days without fog, and were reduced during foggy conditions. For 66% of the data points, [Delta]T and [Delta]q were negative, corresponding to positive (upward) fluxes of sensible heat QH and latent heat QE. A Monte Carlo simulation proved that statistically significant evapotranspiration rates, i.e., upward water vapor fluxes, occurred during fog. At the same time, deposition fluxes of fog droplets occurred. Our results show that even during fog events, significant evapotranspiration may occur. Copyright © 2008 John Wiley & Sons, Ltd.

An analysis of the factors contributing to the settling potential of fine fluvial sediment

N. D. Williams, D. E. Walling, G. J. L. Leeks — 2008-03-20T12:47:00Z

The settling potential of fine sediment is known to be influenced by particle size, shape, density and porosity, and is commonly predicted using Stokes's law, despite its known limitations for modelling the behaviour of natural particles. In order to develop an improved understanding of the potential for fine sediment to settle out of suspension or undergo transport by hydraulic processes, it is important to examine the role of particle structure in detail. In this study, stepwise regression was used to identify which structural properties of particles exert an important control on fine sediment behaviour in river systems. The presence of composite particles and their associated particle size, porosity and fractal dimension were shown to be the most important controls on settling potential. Composite particles that form in the aquatic environment (flocs) were shown to have significantly different form and behaviour from composite particles of terrestrial origin (aggregates). Importantly, it was demonstrated that particle structure and behaviour exhibited consistencies between contrasting river catchments in different locations. An understanding of the mechanisms responsible for the formation of composite particles is viewed as providing a valuable input to efforts to model the mobilisation, transport and fate of fine sediment. Copyright © 2008 John Wiley & Sons, Ltd.

Predicting river width, depth and velocity at ungauged sites in England and Wales using multilevel models

D. J. Booker, M. J. Dunbar — 2008-04-02T11:49:00Z

Using a dataset of gauged river discharges taken from sites in England and Wales, linear multilevel models (also known as mixed effects models) were applied to quantify the variability in discharge and the discharge-hydraulic geometry relationships across three nested spatial scales. A jackknifing procedure was used to test the ability of the multilevel models to predict hydraulic geometry, and therefore width, mean depth and mean velocity, at ungauged stations. These models provide a framework for making predictions of hydraulic geometry parameters, with associated levels of uncertainty, using different levels of data availability. Results indicate that as one travels downstream along a river there is greater variability in hydraulic geometry than is the case between rivers of similar sizes. This indicates that hydraulic geometry (and therefore hydrology) is driven by catchment area, to a greater extent than by natural geomorphological variations in the streamwise direction at the mesoscale, but these geomorphological variations can still have a major impact on channel structure. Copyright © 2008 John Wiley & Sons, Ltd.

Seasonal waves on glaciers

I. J. Hewitt, A. C. Fowler — 2008-05-13T11:04:00Z

Seasonal waves accompanying annual changes in the sliding velocity of ice travel down glacier at speeds much faster than the ice itself. A simple explanation for these waves in terms of the passage of a pressure wave through the subglacial drainage system is given. Drainage by both distributed and localized systems is explored, with the sliding velocity governed by a dependence on the effective pressure. Waves are caused by drainage through a slow distributed system, but may be damped if this is well connected to an efficient channelized system. A possible connection between these waves and high velocity spring events is discussed. Copyright © 2008 John Wiley & Sons, Ltd.

Runoff generation mechanisms in pastures of the Sand Mountain region of Alabama - a field investigation

2008-04-03T10:01:00Z

Excessive application of poultry litter to pastures in the Sand Mountain region of north Alabama has resulted in phosphorus (P) contamination of surface water bodies and buildup of P in soils of this region. Since surface runoff is recognized as the primary mechanism of P transport, understanding surface runoff generation mechanisms are crucial for alleviating water quality problems in this region. Identification of surface runoff generation mechanisms is also important for delineation of hydrologically active areas (HAAs). Therefore, the specific objective of this study was to identify surface runoff generation mechanisms (infiltration excess versus saturation excess) using distributed surface and subsurface sensors and rain gauge. Results from three rainfall events (2·13-3·43 cm) of differing characteristics, and sensor data at four locations with differing soil hydraulic properties along the hillslope showed that the main surface runoff generation mechanism in this region is infiltration excess. Because of this, rainfall intensity and soil hydraulic conductivity were found to play dominant roles in surface runoff generation in this region. Further, only short periods of a few rainfall events during which the rainfall intensity is high produce surface runoff. This study indicates that perhaps subsurface flows and transport of P in subsurface flows need to be quantified to reduce P contamination of surface water bodies in this region. Current studies at this location are identifying spatial and temporal distribution of HAAs, quantifying rainfall characteristics that generate runoff, and estimating runoff volume that results from connected HAAs. Copyright © 2008 John Wiley & Sons, Ltd.

The impact of single natural vegetation elements on flow characteristics

O. Yagci, M. S. Kabdasli — 2008-04-02T11:57:00Z

In this experimental study, measurements were conducted to explore the impacts of different forms of individual natural vegetative elements within the flow domain on velocity and turbulence characteristics. All the experiments were performed in a flume measuring 26 m in length, 0·98 m in width and 0·85 m in depth, and real tree saplings were utilized to represent the vegetation element. In order to analyse this commonly observed nature phenomenon in floodplains, trees with wide trunks were classified into three groups on the basis of their volume versus height relation. Throughout the velocity measurements three acoustic Doppler velocimeters were employed. Time-averaged velocity, streamwise and vertical turbulence intensities and turbulent kinetic energy parameters were examined. Additionally, a formulation that gives the velocity profile at a certain distance downstream of vegetation was introduced and the validity of the proposed formulation was checked with experimental data. It is seen that despite their porous structures, the presence of vegetation considerably disturbs the flow field and dissipates a remarkable amount of energy by turbulence. Copyright © 2008 John Wiley & Sons, Ltd.

Predicting longitudinal dispersion coefficient in natural streams by artificial intelligence methods

Z. Fuat Toprak, Hikmet Kerem Cigizoglu — 2008-03-20T12:07:00Z

In this study, three artificial neural network methods, i.e. feed forward back propagation, the radial basis function neural network, and the generalized regression neural network are employed to compute the longitudinal dispersion coefficient in order to evaluate its behaviour in predicting dispersion characteristics in natural streams. These methods, which use hydraulic and geometrical data to predict dispersion coefficients, can easily be applied to natural streams and are proven to be superior in explaining their dispersion characteristics more precisely than existing equations. This method of predicting the longitudinal dispersion coefficient in river flows was tested on 65 data sets, obtained by researchers from 30 rivers in the USA. Results using the models are compared with results obtained in many other studies, and are shown to be more accurate than the other methods considered. Copyright © 2008 John Wiley & Sons, Ltd.

Periodic changes of stream flow in the last 40 years in Tarim River Basin, Xinjiang, China

Yaning Chen, Zhonghe Pang, Xingming Hao, Changchun Xu, Yapeng Chen — 2008-03-20T12:40:00Z

Using the annual runoff series for the last 40 years from the Tarim River Basin, their periodic properties were analysed and their future trends predicted. Runoff data were collected at five hydrological gauging stations in the three main branches of the Tarim River. An extrapolation method and variance analysis were used to identify periods in annual runoff, and a trend superposition model to predict future changes. Results show that, there is a common period of 17 years in annual runoff changes for all three branches, with Hotan River showing an additional period of 10 years. Based on this trend, it is suggested that the annual runoff of the Tarim River should decrease in the period of 2006-2008, but increase in year 2009, and the flow may possibly begin to decrease significantly in year 2010. The long term trend of runoff in Tarim Basin has followed the global prediction of GCMs, i.e. began to increase in accordance with global increase of air temperature and precipitation in 1990. However, it has shown a local feature of uneven changes among the head streams in the same basin, which needs to be further investigated. Copyright © 2008 John Wiley & Sons, Ltd.

Delineating runoff processes and critical runoff source areas in a pasture hillslope of the Ozark Highlands

M. D. Leh, I. Chaubey, J. Murdoch, J. V. Brahana, B. E. Haggard — 2008-03-20T12:38:00Z

The identification of runoff contributing areas would provide the ideal focal points for water quality monitoring and Best Management Practice (BMP) implementation. The objective of this study was to use a field-scale approach to delineate critical runoff source areas and to determine the runoff mechanisms in a pasture hillslope of the Ozark Highlands in the USA. Three adjacent hillslope plots located at the Savoy Experimental Watershed, north-west Arkansas, were bermed to isolate runoff. Each plot was equipped with paired subsurface saturation and surface runoff sensors, shallow groundwater wells, H-flumes and rain gauges to quantify runoff mechanisms and rainfall characteristics at continuous 5-minute intervals. The spatial extent of runoff source areas was determined by incorporating sensor data into a geographic information-based system and performing geostatistical computations (inverse distance weighting method). Results indicate that both infiltration excess runoff and saturation excess runoff mechanisms occur to varying extents (0-58% for infiltration excess and 0-26% for saturation excess) across the plots. Rainfall events that occurred 1-5 January 2005 are used to illustrate the spatial and temporal dynamics of the critical runoff source areas. The methodology presented can serve as a framework upon which critical runoff source areas can be identified and managed for water quality protection in other watersheds. Copyright © 2008 John Wiley & Sons, Ltd.

Influence of evaporation from the forest floor on evapotranspiration from the dry canopy

2008-05-27T11:37:00Z

Evaporation from the forest floor (Ef) of a secondary broad-leaved forest was monitored for 1 year at 30 min intervals using a closed chamber system. The diurnal and seasonal variation of Ef and forest structure were analysed for days undisturbed by rainfall. The diurnal change in Ef reached a maximum at about 14:00 and gradually decreased towards midnight along with the vapour pressure deficit (D). Although Ef comprised about 20% of evapotranspiration from the dry canopy (Et), it had only a small influence on diurnal evaporation efficiency ([beta]) characteristics above the canopy because its diurnal range was much smaller than that of Et. Although leaf emergence and leaf fall clearly affected available energy (Ae) beneath the canopy, the influence was not clear with Ef. In contrast, seasonal variation in Ef was strongly correlated with D and Ae above the canopy, and the determination coefficient (R2) changed with the Bowen ratio (B). At night, Et was almost equal to Ef when the friction velocity (u*) ranged between 0·2 and 0·4 m s-1. The ratio of Ef to Et was exponentially correlated with leaf area index (LAI) when the soil was not dry. The ratio of Ef to Et was mainly influenced by LAI and soil moisture, but the existence of understory vegetation did not have a strong influence. Copyright © 2008 John Wiley & Sons, Ltd.

Hydrologic prediction for urban watersheds with the Distributed Hydrology-Soil-Vegetation Model

2008-03-20T12:00:00Z

Some relatively straightforward modifications to the Distributed Hydrology-Soil-Vegetation Model (DHSVM) are described that allow it to represent urban hydrological processes. In the modified model, precipitation that falls on impervious surfaces becomes surface runoff, and a spatially varying (depending on land cover) fraction of surface runoff is connected directly to the stream channel, with the remainder stored and slowly released to represent the effects of stormwater detention. The model was evaluated through application to Springbrook Creek watershed in a partially urbanized area of King County, Washington. With calibration, the modified DHSVM simulates hourly streamflow from these urbanized catchments quite well. It is also shown how the revised model can be used to study the effects of continuing urbanization in the much larger Puget Sound basin. Model simulations confirm many previous studies in showing that urbanization increases peak flows and their frequency, and decreases peak flow lag times. The results show that the urbanization parameterizations for DHSVM facilitate use of the model for prediction and/or reconstruction of a range of historic and future changes in land cover that will accompany urbanization as well as other forms of vegetation change. Copyright © 2008 John Wiley & Sons, Ltd.

Precipitation water storage capacity in a temperate mixed oak-beech canopy

Frédéric André, Mathieu Jonard, Quentin Ponette — 2008-04-02T11:45:00Z

The storage capacity of a temperate mixed oak-beech stand was investigated as a function of stand density and species composition. Measurements were performed in selected zones delimited by three neighbouring trees. Three independent approaches were compared: (i) a spraying laboratory experiment to estimate the water storage on foliage before and after dripping; (ii) a mechanistic model describing rainfall partitioning within the forest canopy and providing estimates of foliage storage capacities; and (iii) linear regression analyses to evaluate the canopy (foliage + branches) storage capacity using the relationship between throughfall and rainfall. Good agreement was generally observed between the laboratory experiment and the mechanistic model estimates, while estimations from the regression method tended to exceed those from the other approaches. Storage capacity estimates ranged from 0·22 mm to 0·80 mm for pure oak zones, from 0·24 mm to 1·12 mm for mixed zones and from 0·53 mm to 1·17 mm for pure beech zones. The increase of storage capacity with increasing proportion of beech in the canopy resulted from higher beech LAI compared with oak. Similarly, for mixed and pure beech canopies, storage capacity was higher for high density zones than for low density zones as a result of the increase in LAI with increasing local basal area; in contrast, for pure oak, the storage capacity was not related to basal area because of the lower shade-tolerance of this species compared with beech. Copyright © 2008 John Wiley & Sons, Ltd.

Spatial and temporal perspectives on spring break-up flooding in the Slave River Delta, NWT

B. E. Brock, B. B. Wolfe, T. W. D. Edwards — 2008-03-20T11:11:00Z

Spatial and temporal patterns of spring break-up flooding in the Slave River Delta (SRD), Northwest Territories, are characterized during three years (2003-2005) using water isotope tracers and total inorganic suspended sediment (TSS) concentrations measured from lakewater samples collected shortly after the spring melt. Strongly contrasting spring melt periods led to a moderate flood in 2003, no flooding in 2004 and widespread flooding in 2005. Flooded lakes have isotopically-depleted [delta]18O ([delta]2H) signatures, ranging between - 19·2[permil] (-145[permil]) and - 17·1[permil] (-146[permil]) and most have high TSS concentrations (>10 mg L-1), while non-flooded lakes have more isotopically-enriched [delta]18O ([delta]2H) signatures, ranging between - 18·2[permil] (-149[permil]) and - 10·6[permil] (-118[permil]) and low TSS concentrations (<10 mg L-1). These results, in conjunction with the isotopic signatures of Slave River water and snowmelt, are used to estimate the proportion of river- or snowmelt-induced dilution in delta lakes during the spring of each study year. Calculations indicate river flooding caused dilution of [sim]70-100% in delta lakes, while snowmelt dilution in the absence of river flooding ranged from [sim]0-56%. A positive relationship exists between the spatial extent of spring flooding in the SRD and level and discharge on the Slave River and upstream tributaries, suggesting that upstream flow generation plays a key role in determining the magnitude of spring flooding in the SRD. Parallel variations in the 46-year instrumental Slave River discharge record and flood stratigraphy in the active delta indicate that there is potential for extending the flood history of the SRD, a development that will contribute to a more robust understanding of the drivers of historic, contemporary and future flood frequency in the delta. Copyright © 2008 John Wiley & Sons, Ltd.

Storm-event rainfall-runoff modelling approach for ungauged sites in Taiwan

Yu-Chi Wang, Shien-Tsung Chen, Pao-Shan Yu, Tao-Chang Yang — 2008-03-20T11:06:00Z

This work develops a top-down modelling approach for storm-event rainfall-runoff model calibration at unmeasured sites in Taiwan. Twenty-six storm events occurring in seven sub-catchments in the Kao-Ping River provided the analytical data set. Regional formulas for three important features of a streamflow hydrograph, i.e. time to peak, peak flow, and total runoff volume, were developed via the characteristics of storm event and catchment using multivariate regression analysis. Validation of the regional formulas demonstrates that they reasonably predict the three features of a streamflow hydrograph at ungauged sites. All of the sub-catchments in the study area were then adopted as ungauged areas, and the three streamflow hydrograph features were calculated by the regional formulas and substituted into the fuzzy multi-objective function for rainfall-runoff model calibration. Calibration results show that the proposed approach can effectively simulate the streamflow hydrographs at the ungauged sites. The simulated hydrographs more closely resemble observed hydrographs than hydrographs synthesized using the Soil Conservation Service (SCS) dimensionless unit hydrograph method, a conventional method for hydrograph estimation at ungauged sites in Taiwan. Copyright © 2008 John Wiley & Sons, Ltd.

Use of Nash's IUH and DEMs to identify the parameters of an unequal-reservoir cascade IUH model

Chaoqun Li, Shenglian Guo, Wenhua Zhang, Jun Zhang — 2008-03-20T10:44:00Z

Under the assumption that hydrograph generation was affected by n linear reservoirs with the same value of storage coefficient k, Nash proposed the formulation of the Instantaneous Unit Hydrograph (IUH), which has been widely used in rainfall-runoff simulation and flood forecasting. However, the assumption of the parameter k having the same value in all reservoirs is obviously unphysical as it results in the estimated value of n not being integral. In this study, for parameter n integral, the different k value for each reservoir was derived using the Laplace transform and developing a general rule for the equation of the IUH of any order. The relationship between parameter k and the slope of the river channel estimated using digital elevation model (DEM) data is established, the parameter estimation procedures are given. As in most unit hydrograph studies, only isolated storm events are considered here. Seventeen flood events in three catchments were selected for the case studies. Application results show that the proposed method is slightly better than Nash's IUH with higher model efficiency and smaller absolute relative errors. This work provides a new methodology for the formulation of the IUH. Copyright © 2008 John Wiley & Sons, Ltd.

Variability of shallow overland flow velocity and soil aggregate transport observed with digital videography

A. Sidorchuk, J. Schmidt, G. Cooper — 2008-03-20T10:42:00Z

Field experiments at Tiramoana station 30 km north of Christchurch, New Zealand using an erosion plot 16·5 m long, 0·6 m wide, and with a slope of 14-14·5° on rendzina soil aimed to measure the variability of flow velocity and of soil aggregates transport rate in shallow overland flow. Discharge/cross-section area ratio was used to estimate mean velocity, and high-speed digital video camera and image analysis provided information about flow and sediment transport variability. Six flow runs with 0·5-3·0 L s-1 discharges were supercritical with Froude numbers close to or more than 1. Mean flow velocity followed Poiseuille law, float numbers were more than 1·5 and hydraulic resistance was an inverse proportional function of the Reynolds number, which is typical for laminar flows. Hence actual velocity varied through time significantly and the power spectrum was of 'red-noise', which is typical for turbulent flow. Sediment transport rates had even higher variability, and soil aggregates transport was a compound Poisson process. Copyright © 2008 John Wiley & Sons, Ltd.

Stream flow forecasting using neuro-wavelet technique

Özgür Ki[scedil]i — 2008-03-26T05:38:00Z

This paper proposes the application of a neuro-wavelet technique for modelling monthly stream flows. The neuro-wavelet model is improved by combining two methods, discrete wavelet transform and multi-layer perceptron, for one-month-ahead stream flow forecasting and results are compared with those of the single multi-layer perceptron (MLP), multi-linear regression (MLR) and auto-regressive (AR) models. Monthly flow data from two stations, Gerdelli Station on Canakdere River and Isakoy Station on Goksudere River, in the Eastern Black Sea region of Turkey are used in the study. The comparison results revealed that the suggested model could increase the forecast accuracy and perform better than the MLP, MLR and AR models. Copyright © 2008 John Wiley & Sons, Ltd.

Runoff curve numbers for steep hillslopes with natural vegetation in semi-arid tropical highlands, northern Ethiopia

2008-03-20T10:33:00Z

Daily runoff from 27 plots (5 m × 2 m) recorded during two rainy seasons in the Tigray highlands (Ethiopia) were analysed together with daily rainfall to calculate runoff curve numbers for hillslopes covered by semi-natural vegetation in varying stages of vegetation restoration. Curve number model parameters were derived using a least squares fitting procedure on the collected rainfall-runoff datasets. Curve numbers varied from 29 to 97. Land use type was an important explanatory factor for the variation in curve numbers, whereas hydrologic soil group was not. Curve numbers were negatively correlated with vegetation cover. Taking into account antecedent soil moisture conditions did not improve runoff prediction using the curve number method. As runoff prediction was less accurate in areas with low curve numbers, two separate regression functions relating curve numbers with vegetation cover were proposed for different land use types. Copyright © 2008 John Wiley & Sons, Ltd.

Reconciling theory with observations: elements of a diagnostic approach to model evaluation

Hoshin V. Gupta, Thorsten Wagener, Yuqiong Liu — 2008-03-11T12:44:00Z

This paper discusses the need for a well-considered approach to reconciling environmental theory with observations that has clear and compelling diagnostic power. This need is well recognized by the scientific community in the context of the 'Predictions in Ungaged Basins' initiative and the National Science Foundation sponsored 'Environmental Observatories' initiative, among others. It is suggested that many current strategies for confronting environmental process models with observational data are inadequate in the face of the highly complex and high order models becoming central to modern environmental science, and steps are proposed towards the development of a robust and powerful 'Theory of Evaluation'. This paper presents the concept of a diagnostic evaluation approach rooted in information theory and employing the notion of signature indices that measure theoretically relevant system process behaviours. The signature-based approach addresses the issue of degree of system complexity resolvable by a model. Further, it can be placed in the context of Bayesian inference to facilitate uncertainty analysis, and can be readily applied to the problem of process evaluation leading to improved predictions in ungaged basins. Copyright © 2008 John Wiley & Sons, Ltd.