Assessment of the effects of land use/cover change on streamflows: a case study of Ndjili River Basin, DRC

Ndjili River basin with an area of 2088 km2 in DRC has been threatened by uncontrolled development activities such as informal settlements, deforestation, vegetation clearance and mining. Modifications of natural vegetation cover and soils conditions usually lead to changes in rainfall-runoff characteristics of the basin. The changes in rainfall-runoff patterns consequently change the river flow regimes. The aim of the study was to evaluate how land use and land cover changes have affected the hydrology of Ndjili River. Two scenarios of land cover were analyzed from landsat images of 1987 and 2001 using ENVI and ArcGIS software. Ten rainfall stations were selected as input data for the rainfall-runoff model. The calibration was done for the year 2005 with streamflow data from the Ndjili gauging station. Thiessen weight method was used to reflect spatial characteristics of rainfall distribution. Hydrologic parameters were computed through the HEC-GeoHMS and spatial data processed with a DEM 30-m resolution. The USACE HEC-HMS was used for estimating streamflow. Clark transform method was adopted for calculating runoff while the Soil Moisture Accounting (SMA) was used for loss method. The results from the model calibration yielded a NSCE of 0.85. The analysis showed that between 1987 and 2001, vegetation was reduced by 8% while agricultural land and urbanization have increased by 1.4% and 4% respectively. The mean flow under the 1987 and 2001 land cover was 19.5 m3/s and 21 m3/s respectively; the peak flow was 101 m3/s and 128.7 m3/s respectively and they were close to the 25 years return period streamflow. The model predicts that changes in land-use will increase the peak streamflow, and the increase is directly proportional to the rate of urbanization.