Prediction of runoff and discharge in the Simiyu River (tributary of Lake Victoria, Tanzania) using the WetSpa model

Abstract

Abstract. A spatially distributed hydrologic model (WetSpa) is used to estimate daily river water discharge in the Simiyu river a tributary of Lake Victoria, Tanzania. The model combines topography, landuse and soil maps, and observed daily meteorological time series to predict discharge hydrographs and the spatial distribution of hydrological parameters in the catchment. The elevations in the catchment range from 2000 to 1100 m at the outlet, with average slope of 1.4%. The dominant landuse types are, wasteland, grassland, bushland, cultivated land, and a very small area is covered by surface water. The dominant soil types are sandy loam, followed by sandy clay loam, clay loam, clay, loam and sandy clay. There are two distinctive seasons in the Simiyu catchment. Short rains mainly in November, December and January, and long rains in March to May, resulting in a total average annual precipitation of 700 to 1000 mm. The annual potential evapotranspiration is about 1300 mm, and the river discharge at the catchment outlet ranges from 0 to about 200 m3/s. Global parameters of the model are calibrated using three years of daily observed discharge values measured at the mouth of the river at Lake Victoria. The estimated average travel time of the runoff to the outlet of the catchment is about 2.4 d and maximum 8 d for the most remote areas. The model results also show that the surface runoff and interflow provide respectively 38.6% and 61.4% of the total runoff, while the contribution of groundwater drainage is nil. The absence of groundwater drainage is probably due to the high evaporation demand of the atmosphere, which accounts for about 90% of the total precipitation being lost by evapotranspiration. The annual water balance estimated with the model reveals that the total outflow to Lake Victoria is about 500×106 m3 per year, which occurs mainly in the wet seasons, i.e. from March to May and from November to January. The volume of runoff produced by agricultural land amounts to about 9% of the total runoff annually.

A Lagrangian perspective of the hydrological cycle in the Congo River basin

“…During the next few months, the precipitation and runoff decrease while the discharge increases, reaching a maximum in May. This lag should reflect both the required time for the surface runoff to reach the river mouth and the groundwater contribution (Dai and Trenberth, 2002;Dai et al, 2008;Marengo, 2005;Rwetabula et al, 2007;Sear et al, 1999), as documented by Materia et al (2012), who used data that were recorded at the Brazzaville station approximately 400 km upstream of the river mouth. The direct relationship between the precipitation over the basin and the discharge has a correlation of 0.52, which increases to 0.66 for a 1-month lag (both statistically significant at p < 0.05), confirming the aforementioned lagged response.…”

Water temperature controls in low arctic rivers

“…Incorporation of subsurface lateral inflows and hyporheic exchange into the current temperature modeling effort could buffer river temperature and improve modeled diurnal temperature fluctuations (supporting information Tables S4 and S6). Regression analyses and hydrologic models may prove valuable for estimating lateral inflow temperature and discharge from meteorological conditions [Flint and Flint, 2008;Pohl et al, 2007;Rwetabula et al, 2007;Webb et al, 2003].…”

Stream flow Simulation by Wetspa Model in Garmabrood Watershed of Mazandaran Province, Iran

“…According to calibration results, model outperforms under high flow compared to high flow which this may be attributed to model weakness in low flow estimation but as a whole model simulated total flow with acceptable accuracy. In this case, small Nash -Sutcliffe coefficient for low flows can be found in elsewhere [10], [3] and [8]. However validation results are unacceptable and this may be due to the model structure or data and basin conditions.…”

“…Statistical analysis of hydrographic derived from model and observed hydrograph showed that model can well predict its normal and flood currents. Reference [8] applied WetSpa hydrological model to predict runoff flow in Simiu, in the area of Lake Victoria in Tanzania. The results of the model showed that model can route flow in river.…”