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Insufficient sub-surface hydraulic data from watersheds often hinders design of water resources structures. This is particularly true in developing countries and in watersheds with low population densities because well-drilling to obtain the hydraulic data is expensive. The objective of this study was to evaluate the applicability of ‘Brutsaert’ recession flow analysis to steeper and more arid watersheds than those that were previously used. Using daily streamflow data (1962–1992), a modified version of the analysis was used to estimate the subsurface hydraulic parameters of four semi-arid, mountainous watersheds (204–764 km2) near Oaxaca, Mexico. In this analysis, a dimensionless recession curve (DRC) was translated to best-fit observed recession flow (Q) data. The basin-wide hydraulic parameters were directly related to the magnitude of the translation used to fit the DRC to the data. One unique aspect of this study was too few high flow data to confidently fit the DRC to the data via previously published protocols. We, thus, proposed using three different approaches for translating the DRC in order to establish a range for the hydraulic parameters. Our analyses predicted a narrow range of basin-wide hydraulic parameters that were near regionally measured values and consistent within commonly published values for similar geology, suggesting that the Brutsaert method is applicable to arid, mountainous basins like those used here. This method potentially provides a cost-effective alternative to traditional geohydrological field methods for determining groundwater parameters. [Copyright &y& Elsevier]

Soil and water conservation structures, promoted by local and international development organizations throughout rural landscapes, aim to increase recharge and prevent degradation of soil surface characteristics. This study investigates this unexamined relationship between recharge, water table depths, and soil surface characteristics (nutrients) in a small sub-watershed in the northwestern Ethiopian highlands. These highland watersheds have high infiltration rates (mean 70 mm hr −1 , median 33 mm hr −1 ), recharging the shallow unconfined hillslope aquifer with water transport occurring via subsurface pathways down the slope. The perched water tables reflect the subsurface flux and are deep where this flux is rapid in the upland areas (138 cm below surface). Soil saturation and overland flow occur when the subsurface flux exceeds the transport capacity of the soil in the lower downslope areas near the ephemeral stream (19 cm below surface). Land use is directly related to the water table depth, corresponding to grazing and fallowed (saturated) land in the downslope areas and cultivated (unsaturated) land in the middle and upper parts where the water table is deeper. Kjeldahl Total Nitrogen (TN), Bray II available phosphorus (AP), and exchangeable potassium (K + ) averages exhibit different behaviors across slope, land use transects, or saturation conditions. TN was moderate to low (0.07% ± 0.04) in various land uses and slope regions. Bray II AP had very low concentrations (0.25 mg kg −1  ± 0.26) among the different slope regions with no significant differences throughout (p > .05). The exchangeable cation (K + , Ca 2+ , Mg 2+ ) concentrations and pH, however, were greater in non-cultivated (seasonally saturated) lands and in a downslope direction (p < .001, p < .005, p < .05, and p < .005, respectively). These results show that the perched groundwater plays an important role in influencing land use, the amount of water seasonally available for crop growth, and exchangeable cations, but have no clear effect on the concentration of the two primarily applied nutrients in fertilizers (N, P). [ABSTRACT FROM AUTHOR]

Summary In response to anthropogenic disturbances, alluvial rivers adjust their geometry. The alluvial river channels in the upper Blue Nile basin have been disturbed by human-induced factors since a longtime. This paper examines channel adjustment along a 38-km stretch of the Gumara River which drains towards Lake Tana and then to the Blue Nile. Over a 50 years period, agriculture developed rapidly in the catchment and flooding of the alluvial plain has become more frequent in recent times. The objectives of this study were to document the changes in channel planform and cross-section of the Gumara River and to investigate whether the changes could have contributed to the frequent flooding or vice versa. Two sets of aerial photographs (1957 and 1980) were scanned, and then orthorectified. Recent channel planform information was extracted from SPOT images of 2006 and Google Earth. Channel planform and bed morphology (vertical changes) were determined for these nearly 50 years period. The vertical changes were determined based on aggradation along a permanent structure, historic information on river cross-sections at a hydrological gauging station, and field observations. The results indicate that the lower reach of Gumara near its mouth has undergone major planform changes. A delta with approx. 1.12 km 2 of emerged land was created between 1957 and 1980 and an additional 1 km 2 of land has been added between 1980 and 2006. The sinuosity of the river changed only slightly: negatively (−1.1% i.e. meandering decreased) for the period from 1957 to 1980 and positively (+3.0%) for the period 1980–2006. Comparison of cross-sections at the hydrological gauging station showed that the deepest point in the river bed aggraded by 2.91 m for the period 1963–2009. The importance of sediment deposition in the stream and on its banks is related to land degradation in the upper catchment, and to artificial rising of Lake Tana level that creates a backwater effect and sediment deposition in Gumara River. Direct anthropogenic impacts (irrigation activities and building of dykes along the river banks) have contributed to the huge deposition in the river bed. Where the abstraction of water for irrigation is intensive, seepage water through the banks has contributed to river bank failure. In general, this study showed that changes to the planform at the mouth of the river and to the riverbed level are substantial. Moreover, the study indicated that the flood carrying capacity of the Gumara River channel has diminished in recent times. [ABSTRACT FROM AUTHOR]

• SWAT-C predicts dissolved organic carbon (DOC) export from variable source areas. • Remotely sensed data reduced uncertainty in model predictions. • DOC predictions are sensitive to soil properties. • DOC flux is more sensitive to increases in precipitation than air temperature. Dissolved organic carbon (DOC) in surface water influences the global carbon cycle, ecosystem productivity, and water quality in potable water supply systems. Few physically based watershed models can simulate carbon cycling and predict DOC in surface waters under the influence of natural and anthropogenic drivers. In this work we transform the SWAT-Carbon (C) model to simulate DOC from variable source runoff areas in a humid forested watershed in the northeastern United States. Remotely sensed data were used to parameterize and simulate forest growth and evapotranspiration. The calibrated model accurately simulated streamflow and DOC flux at six sites across the watershed compared to measured data. The DOC predictions across sites showed model sensitivity to soil properties, particularly soil depth and available water capacity. The spatial distribution of DOC export across the watershed followed the pattern of surface runoff from variable source areas. Model sensitivity of DOC flux showed greater sensitivity to changes in precipitation than temperature. The overall good performance of the model makes it a valuable tool for watershed-scale modeling of DOC to understand the influence of climate and watershed management towards developing mitigation strategies. The methods presented in this study can be used in forested watersheds in regions where runoff from variable source areas is important for water quality predictions. [ABSTRACT FROM AUTHOR]

Because water shortages limit development in many parts of the world, a systematic approach is needed to use water more productively. To address this need, Molden and Sakthivadivel [Water Resour. Dev. 15 (1999) 55-71] developed a water-accounting procedure for analyzing water use patterns and tradeoffs between users. Their procedure treats groundwater and surface water as a single domain. We adapted this procedure to account for groundwater and surface water components separately, and applied the adapted procedure to the Singkarak–Ombilin River basin, Indonesia, where groundwater is a significant part of the overall water balance. Since 1998, a substantial proportion of water has been withdrawn from Singkarak Lake and diverted out of the basin, resulting in significant impacts on downstream water users and the lake ecosystem. Based on 15–20 years (1980–1999) of hydrometeorological, land use, soil, and other relevant data, a simple groundwater balance model was developed to generate the hydrogeologic information needed for the water-accounting procedure. The water-accounting procedure was then used to evaluate present and potential future water use performance in the basin. By considering groundwater and surface water components separately, a more realistic estimate of water availability was calculated than could be obtained by lumping these components together. Results show that the diversion of 37 m3/s from Singkarak Lake increases the amount of water that is not available for other uses, such as for irrigation, from 57–81 to 81–95% of total water available in the basin. The new water accounting procedure also demonstrates the viability of increasing downstream water supply and water use performance during the dry months (June–September). For example, by increasing irrigation during the wet months (January–April) or tapping water from a shallow, unconfined aquifer during the dry months, while keep maintaining sustainable groundwater levels. [Copyright &y& Elsevier]

Differences in the simulation of hydrologic processes by watershed models directly affect the accuracy of results. Surface runoff generation can be simulated as either: (1) infiltration-excess (or Hortonian) overland flow, or (2) saturation-excess overland flow. This study compared the Hydrological Simulation Program—FORTRAN (HSPF) and the Soil Moisture Routing (SMR) models, each representing one of these mechanisms. These two models were applied to a 102 km2 watershed in the upper part of the Irondequoit Creek basin in central New York State over a seven-year simulation period. The models differed in both the complexity of simulating snowmelt and baseflow processes as well as the detail in which the geographic information was preserved by each model.Despite their differences in structure and representation of hydrologic processes, the two models simulated streamflow with almost equal accuracy. Since streamflow is an integral response and depends mainly on the watershed water balance, this was not unexpected. Model efficiency values for the seven-year simulation period were 0.67 and 0.65 for SMR and HSPF, respectively. HSPF simulated winter streamflow slightly better than SMR as a result of its complex snowmelt routine, whereas SMR simulated summer flows better than HSPF as a result of its runoff and baseflow processes.An important difference between model results was the ability to predict the spatial distribution of soil moisture content. HSPF aggregates soil moisture content, which is generally related to a specific pervious land unit across the entire watershed, whereas SMR predictions of moisture content distribution are geographically specific and matched field observations reasonably well. Important is that the saturated area was predicted well by SMR and confirmed the validity of using saturation-excess mechanisms for this hillslope dominated watershed. [Copyright &y& Elsevier]