Estimation of Sustainable Water Resources Potential of Ikpa Sub-Watershed Using GIS And NRCS (SCS) Approaches

The knowledge of water quantity that a watershed yields enables planning for its utilization and effective management for sustainability. Lack of adequate water infrastructures within Ikpa watershed and overstretched existing infrastructure problems have led to avoidable water related health hazards in Ikpa watershed. There is dearth of information on the quantification of water yield availability within the watershed. The study was therefore designed to estimate water resources potentials of the Ikpa watershed. Shape and drainage network of the watershed were determined using Geographic Information System (GIS). Data from Nigerian Meteorological Agency were used to estimate the watershed’s water quantity using water balance model. Watershed physiographical characteristics were determined, while surface water quantities were estimated using National Resources Conservation Service - Soil Conservation Service (NRCS - SCS), GIS and Remote Sensing (RS) approaches. Pearson correlation analysis was used to forecast rainfall–runoff magnitudes. Best fitted probability distribution functions to the watershed were determined using three different plotting methods at four different return periods. Ikpa watershed is fern shaped with dendritic drainage network of stream order 4. Physiographical parameters of the watershed were as follows: area (360.56 km2), total length (158.23 km), average runoff coefficient (0.36), average slope (0.11) and average concentration time (0.06 min). Estimated surface water quantities with NRCS-SCS and GIS were 2.96 billion m3 and 4.89 billion m3, respectively and subsurface water quantity was 37.2 billion m3. Total annual potable water potential was obtained to be 24.12 billion m3 with 12.27% accounting for the surface water quantity. Human population within the watershed was 245,663. It was observed that 0.05% of the total water resources available was utilized annually, indicating underutilization of the available water. The overall available water resources within Ikpa watershed are fairly sustainable. The water resources potential was grossly underutilized and could be harnessed for beneficial use