7th Annual WaterNet/WARFSA/GWP-SA Symposium
1-3 November 2006, Capital Hotel, Lilongwe, Malawi.
WaterNet Secretariat symposium07@eng.uz.ac.zw
Sub-theme 1: Hydrology Poster Presentation
Simulation of daily streamflow for sub-catchments of the Upper Tana River Basin, Kenya
using a conceptual rainfall-runoff model
John K. Mwangi.*, John M. Gathenya**, and Christopher M. Ondieki ***
*Department of Civil Engineering, Jomo Kenyatta University of Agriculture
And Technology, Kenya
**Department of Biochemical and Environmental Engineering, Jomo Kenyatta
University of Agriculture and Technology, Kenya (corresponding author)
***Department of Geography, Kenyatta University, Kenya
ABSTRACT
Streamflow measurements are important for water resources management. They are required for
designing diversion structures, bridges, dams, flood control structures and for assessment of
environmental flows. In Kenya, inadequate streamflow data presents challenges to water
resources management. Rive gauging stations are insufficient, irregularly distributed or have data
with gaps. Application of rainfall-runoff models to the catchments can be used to generate
streamflow data. However, this requires some basic data for model calibration and validation. A
lumped conceptual rainfall-runoff model IHACRES was applied to six medium sized catchments
in the Upper Tana Basin of Kenya. The model IHACRES was chosen because it requires only
catchment area, streamflow data and a surrogate variable representing evaporation such as
temperature. In addition it has only two parameters to be varied during the calibration.
Streamflow data for the six catchments spanning six years was used in the present study. The
data was split into two sets for calibration and validation purposes. A daily time step was
adopted. After calibration, dynamic response characteristics were obtained from which
streamflow could be simulated. Simulated streamflow was then compared with the observed
streamflow for these catchments and the goodness of fit evaluated using both statistical and
graphical methods. Sensitivity analysis tests were also carried out using results for one of the
catchments. Consequently, flow response to variations in model parameters was assessed in
order to analyze calibration errors. The results obtained for all the catchments showed that
IHACRES model was capable of simulating daily streamflow given concurrent daily rainfall and
temperature data and that the method offers possibility of filling in missing data or generating a
long series of streamflow data for water resources management in the Upper Tana River basin.