JoSHJournal of Spatial Hydrology     ISSN: 1530-4736

An official publication of American Spatial Hydrology Union (ASHU)             

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     Vol. 10. No. 1 Spring 2010

     Vol. 9, No.2 Fall 2009
     Vol. 9, No.1 Spring 2009

     Vol. 8, No.2 Fall 2008
     Vol. 8, No.1 Spring 2008

     Vol. 7, No. 2 Fall 2007
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     Vol. 6, No. 2 Fall 2006
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     Vol. 5, No. 2 Fall 2005
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     Vol. 3, No. 2 Fall 2003
     Vol. 3, No. 1 Spring 2003

     Vol. 2, No. 2 Fall 2002
     Vol. 2, No. 1 Spring 2002

     Vol. 1, No. 1 Fall 2001
 

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Abstract The goal of this paper is to assess the impact of future climate change on the hydrological regime of the tropical Upper Suriname river basin (7,860 km2) located in Suriname. GCM based climate scenarios from the MAGICC/SCENGEN model and 14 hypothetical climate scenarios are used to examine potential changes in water balance components in the study area. A physically-based distributed hydrological model, WetSpa, and Geographic Information Systems (GIS) are used to simulate the historical and future hydrological conditions. The evaluation results indicate that the model has a relatively high confidence (model bias C1 is 0.046 and the model determinant coefficient C2 is 0.833) and can give a fair representation of the river flow hydrographs at daily scale (Nash Sutcliffe coefficient C3 is 0.622). The results indicate that an obvious increase in the annual temperature (1.8oC and 3.2oC by 2050 and 2080 respectively) in the study area is accompanied with a clear tendency in reduced precipitation during January-March and August-December, and an increased tendency during April-July. The sensitivity analyses of water balance components under temperature and precipitation change (GCM scenarios for 2050, 2080) shows that by 2080, the annual river discharge will drop 35%. The hypothetical climate scenarios (T+2oC, T+4oC and P+10%, +30%, +50%) however indicate that the annual river discharge will increase with maximum 75% for the scenario T+2oC P+50% and will decrease with maximum 87.5% for the scenario T+2oC P-50%. The results are indications of potential impacts of climate change on water resources in the Upper Suriname river basin, but true predictive skills require a significant improvement in the ability of global climate models to predictive changes in regional climate variability. The WetSpa model has proven to be useful for hydrological modeling studies where availability of physical catchment characteristics and hydroclimatic data is scarce.

Keywords: Climate Change; Climate Change Scenarios; Geographic Information Systems; Global Circulation Models; Hydrologic Modeling; Upper Suriname river basin.

ABSTRACT The Upper Tana River Basin is one of Kenya’s most important natural resource bases. Its Masinga Reservoir supplies water and hydroelectric power for 65 percent of the nation.  Unregulated deforestation and expansion of cultivation practices onto marginal soils has resulted in significant reservoir siltation, reduced ecosystem function, and more erratic downstream flows.  An appraisal conducted for this study identified potential areas where reforestation could occur, enabling a doubling of the reforested areas currently in the Upper Tana River catchments.  The Soil and Water Assessment Tool (SWAT) model was used to evaluate alternative reforestation scenarios.  An economic model was developed to determine the opportunity costs associated with reforestation and the economic incentives, i.e. green payments, which would be required to induce upper catchment users to reforest. The analysis found that reforestation would decrease sediment loading in the Masinga Reservoir by 7 percent. Users in the upper catchment would be paid $33 for each ton of sediment they retained in their fields, but benefits were found to be insufficient for downstream users to sponsor green payments. Under an alternative price structure that targeted green payments to specific upstream producer groups the downstream benefits would increase, providing adequate incentives to implement green payments. The findings of this research can assist environmental policy implementation by the Kenyan government that will foster improved environmental results.

Key Words: reforestation, Kenya, Tana River, SWAT, erosion, runoff, green payments.

Abstract An export coefficient approach to hydrological and non-point source (NPS) pollution modeling enables quick and simple assessment of long-term impacts for planning purposes. An export coefficient and geographic information system based L-THIA (Long-Term Hydrologic Impact Assessment) model was applied to the Richland Creek basin (Illinois, USA) to assess the impacts of future urban growth on direct runoff, NPS total nitrogen (TN), total suspended particles (TSP), and total phosphorous (TP) loads. The model predicted that mean annual direct runoff and TSP loading would increase by around 7% and 4% respectively by 2030 with moderate and rapid urban growth simulated by a land-use change model, while TN and TP loads would change little. Such changes are due to the projected land-use change patterns, mainly from agriculture to commercial/industrial or low-intensity residential, and to the different contributions of land-uses to runoff and NPS pollutant loads. At a subbasin scale, the most developed subbasin is projected to experience the greatest increase in commercial/industrial land at the expense of agricultural land and thus notable increases in runoff and TSP load. The changes in runoff and TSP load in other subbasins and the changes in TN and TP loads in all the subbasins show little spatial variability even though the range of per cent increases in low-intensity residential is extremely wide. This study reveals the effect of different ‘urban’ land-use types on water quality and suggests that proper simulation or planning of different urban land-use types must be carried out for impact assessments.

Keywords: land-use change; runoff; non-point source pollution; hydrological model

Abstract In a complex watershed, isolated wetlands, riparian wetlands and riparian buffers provide important functions such as flood attenuation and water quality improvement. For conservation purposes, it is critical to properly delineate drainage areas for these features such that their impacts on runoff, sediment and pollutant transport can be reasonably simulated. However, traditional methods for watershed delineation typically fill depressions or ignore riparian features in order to maintain the continuity of surface flow pattern. In this study we develop an ArcView geographic information system (GIS) interface for watershed delineation that accounts for wetlands and riparian buffers. Based on digital elevation model (DEM), wetland distribution, and stream network GIS data, a subwatershed is further divided into isolated wetland drainage, concentrated flow drainage, riparian wetland drainage, and direct stream drainage. Outflow from isolated wetlands forms a source of concentrated flow that may contribute to riparian wetlands or bypass riparian buffers depending on its outlet location. This approach of drainage division makes a contribution in linking watershed models and field-based models through divided drainage areas. The developed interface provides a tool for simulating hydrologic processes of these features and assessing different restoration scenarios. The drainage division interface is applied to the Fairchild Creek watershed of southern Ontario in Canada where numerous isolated wetlands, riparian wetlands and riparian buffers exist. A comparison of runoff and sediment simulation results before and after drainage delineation shows the importance of the interface in facilitating watershed modeling. 

Keywords: Drainage division, DEM, GIS, wetlands, riparian buffers, concentrated flow

Abstract The hydrodynamics and the long-term water balance of two topographically closed crater lakes is presented in a comparative manner using a spread-sheet hydrological model. The main objective of the work is to study the role of groundwater and the effect of water abstraction from lakes Awassa and Naivasha. The rationale of selection of the two lakes separated by thousands of kilometers is the striking similarity of their hydrogeological and geomorphological setting and future intended water uses for large-scale abstraction from the lakes and feeder rivers. The net groundwater outflow from Lake Awassa and the effect of water abstraction from Lake Naivasha under different scenarios were calculated based upon the average monthly hydrometeorological data of rainfall, evaporation and river inflows. The net groundwater flux was obtained from the simulation as a residual of other water balance components and was found to be substantial in both lakes. The result revealed that the annual net groundwater outflow from Lake Awassa to adjacent basins is estimated at 58 ×106 m3. The predicted and recorded lake levels fit well for much of the simulation period. For Lake Naivasha groundwater flows into and out of the lake are successfully estimated based on the predicted water level fluctuations when water abstraction was at a minimal. The most accurate predictions of lake level were derived from the data sets of river discharges known to be from the most-reliable time period after the early 1970s. The model estimated an annual abstraction rate and groundwater outflow from Lake Naivasha of 60×106 m3 and 56×106 m3 respectively. The model demonstrated its validity as a good management tool to predict effects of large-scale pumping and extreme climatic events that may affect the lakes in space and time.

 Key Words:  Awassa, East African rift, hydrology, modeling, Naivasha, water balance

Abstract Geographic Information System (GIS) was utilized to apply a modified DRASTIC method to assess the aquifer vulnerability to pollution of English Bazar Block of Malda District, West Bengal, India. In the western, central and southern parts of the study area the aquifer is prone to contamination. Therefore, in these regions pesticides, which may contain arsenic or arsenic rich groundwater, should not be used in irrigated land or mango orchards. In order to understand the reliability of the aquifer vulnerability, sensitivity analysis was carried out. This analysis indicates that in 62% of the area the vulnerability classes correspond to the present arsenic concentration in groundwater.

 Keywords: DRASTIC, vulnerability, arsenic, groundwater, Malda, West Bengal

Abstract Any reduction in water spread area at a specified elevation over a time period is indicative of sediment deposition at this level. This when integrated over a range of water stages helps in computing volume of storage lost through sedimentation.  This study relates to estimation of capacity loss due to sedimentation of Hirakud reservoir, located in Orissa, India. Satellite data of 5 optimal dates corresponding to various water stages from minimum to maximum draw down levels were used in estimating the water spread areas. Simple ratiod (NIR/RED) image were generated to identify the water pixels and then verifying the standard FCC. The non-water pixels were then identified with the ratiod (GREEN/NIR) image and removed to have the total water spread. The water spread area on different satellite overpass dates and corresponding elevations were then used to find the total reservoir storage capacity with the help of Elevation area curve.