Modelling the Mara River Basin with data uncertainty using water levels for calibration

Abstract

Abstract. Hydrological models play an important role in Water Resources Management. In hydrological modelling, discharge data is generally required for calibration. To obtain continuous time series, water levels are usually converted into discharge by using a rating curve. However with this methodology, uncertainties are introduced in the discharge data due to insufficient observations, inadequate rating curve fitting procedures, 10 extrapolation or temporal changes in the river geometry. Unfortunately, this is often the case in many African river basins. In this study, a semi-distributed rainfall runoff model has been applied to the Mara River Basin for the assessment of the water availability. To reduce the effect of discharge uncertainties in this model, water levels instead of discharge time series were used for calibration. In this model, seven sub-catchments are distinguished and four hydrological response units: forest, shrubs, cropland and grassland. To calibrate the 15 model on water level data, modelled discharges have been converted into water levels using cross-section observations and the Strickler formula. In addition, new geometric rating curves have been obtained based on modelled discharge, observed water level and the Strickler formula. This procedure resulted in good and consistent model results during calibration and validation. The hydrological model was able to reproduce the water depths for the entire basin as well as for the Nyangores sub-catchment in the north. The geometric and 20 recorded (i.e. existing) rating curves were significantly different at Mines, the catchment outlet, probably due to uncertainties in the recorded discharge time series. At Nyangores however, the geometric and recorded discharge were almost identical. In addition, it has been found that the precipitation estimation methodology influenced the model results significantly. Application of a single station for each sub-catchment resulted in flashier responses whereas Thiessen averaged precipitation resulted in more dampened responses. In conclusion, 25 by using water level time series for calibrating the hydrological model of the Mara River Basin promising model results were obtained. For this river basin, the main limitation for obtaining an accurate hydrograph representation was the inadequate knowledge on the spatial distribution of the precipitation.Hydrol. Earth Syst. Sci. Discuss., https://doi

Humans reshape wetlands: Unveiling the last 100 years of morphological changes of the Mara Wetland, Tanzania

“…While the Lower Mara is poorly gauged, available data of WSL and rainfall are still useful to date flow peaks. Discharge and WSL daily data from the MM measuring station and WSL daily data from the KB measuring station have been obtained from the Lake Victoria Basin Water Office (LVBWO) of the Tanzanian Ministry of Irrigation and from previous works (Hulsman et al, 2017;McClain et al, 2014). WSL data from MM are available for the period 1969 -2018, having gaps in the periods 1991 -2005 and 2008.…”

“…For this reason, it was measured a few times for this study (see section 3.4.2). Available daily and monthly rainfall data covering the time between 1901 and 2009 have been gathered from 25 stations along the entire basin (Dessu et al, 2014;Dessu and Melesse, 2013;Hulsman et al, 2017;Wenninger and Venneker, 2017). Monthly data range from 1901 to 2009 and daily data from 1959 to 2009.…”