Download GROUNDWATER MODELING IN LAKE NAIVASHA WATERSHED

GROUNDWATER MODELING IN LAKE NAIVASHA WATERSHED
Lake Naivasha watershed is found in Nakuru County, Kenya. It located within the
east African rift system (specifically In the Gregory rift). The rocks in the
watershed area are mainly volcanic, which display various fault structures. Owor,
(2000) argues that faulting has two effects on groundwater flow; they provide
channels of high permeability or may prove to be barriers to flow by offsetting
zones of relatively high permeability. The objective of this study is to construct a
groundwater model that will help in understanding the flow mechanism of
groundwater in the watershed area.
The model is developed using processing MODFLOW (Pmwin 5.3) software, and
covers an area of approximately 2035 Km 2 . The data used in this project include
rainfall data from Kenya meteorological department, XYZ coordinate file from
digitized topographical map of Naivasha and values of hydraulic properties of
various rock types in the study area from previous geological works (See appendix
1).
In the modeling process, the study area is represented by a grid which is divided
into35 columns and 37 rows. The size of the grid is 100 metres. The grid contains
1021 active and 1014 inactive cells.
The boundary conditions of the area are specified using the surface water divides.
A no flow boundary is assigned along the watershed boundary assuming that the
groundwater flow across the surface water divides is negligible. Lake Naivasha is
specified as a fixed head boundary.
A piezometric contour map for the simulated heads is produced at the end of the
modeling process, which shows the distribution of heads. Path lines (arrows) are
drawn in the piezometric contour map to indicate the flow pattern of groundwater.
Groundwater generally flows from regions of high heads (Catchment areas)
towards regions of low heads (Lake region). Most of the flow in the study area is
from the northern part of the catchment. This project serves as a starting point for
detailed modeling in the watershed area.