Hydrological Modelling in Ungauged Catchment (In Case Suluh), Tigray

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Addis Ababa University


The study area of suluh catchment have the scarcity of record data, but the Suluh River have the capability of feeding the society nearby as source of small scale hydropower and irrigation. In addition to that since it is ungauged catchment it has no representing model of Rainfall- runoff relation and water harvesting structure. The work described here will attempt to solve these problems using the regional approach whereby statistically homogeneous regions are identified and the parameters of choosing distribution are estimated from the regional averages so that the flow quantile for the ungauged catchment within that region can easily be computed. So that the necessity of this study arises from the weight to improve site specific estimates based on limited data and to make inference about ungauged catchments. In ungauged catchments, model parameters have to be estimated from other sources of information. An appealing way to estimate model parameters in ungauged catchments is to glean the model parameters from hydrologically similar catchments. Hydrological modeling in ungauged catchments often involves the transfer of calibrated model parameters from donor (gauged) catchments to the receiver (ungauged). However, in any hydrological modeling, some parameters tend to be more sensitive to the objective function, whereas others are insensitive. Sensitivity analysis was performed to choose the most sensitive flow parameters that influence the catchment represented by SWAT to be used for calibration. This was achieved using the global sensitivity approach in semi-automated Sequential Uncertainty Fitting (SUFI2) algorithm. The global sensitivity analysis method takes into consideration, the sensitivity of one parameter relative to the other in order to give their statistical significances. The t-statistics and p-values of the parameters were used to rank to the different parameters considered to influence flow and the final selection done based on the significance of the ranked values. Table4 shows stream flow parameters that were tested for their sensitivity. These are useful in estimating the amount of flow from a catchment. The global sensitivity analysis of 21 flow parameters showed that, only eight were very sensitive to flow. Although, the rest of the parameters were found not to be sensitive to flow in the catchment as their p-values were greater than 5%. The Time period of 2000-2009 is used for SWAT model Calibration, and the 2009-2014 period for validation. Time series plots, as well as statistical measures, such as the coefficient of determination (R2) and the Nash-Sutcliffe efficiency (NS) parameter between observed and simulated stream flows are computed on monthly time scales and indicate a good performance of the final calibrated SWAT model. From the SWAT model output around 85% of the Suluh flow indicates surface runoff. The maximum rainfall of the catchment is about 331mm during a month of August and Similarly with surface runoff of 98.3mm.



Ungauged Catchment, Suluh, Transfer, SWAT, Calibration, Validation, Stream flow