Groundwater Level Variability in Ruiru Location, Kiambu County, Kenya

Abstract

Groundwater accounts for the largest fresh water resources in the world. However, there has been limited exploitation of this vital resource in many areas. Where groundwater resources have been exploited, there has been over-exploitation, pollution, wastage and mismanagement. About a third of Kenya’s population has no access to potable water. In Ruiru location,rising population and industrial development has led to a high water demand and increased water scarcity. Groundwater from boreholes is a major source of water supply contributing about 70% of the water requirements. Analysis on water supply in the location done by RuiruJuja Water and Sewerage Company (RUJWASCO), shows that even after completion of Jacaranda dam, water demand cannot be met in the location. In addition, declining borehole water levels and drying up of wells during the dry season has become a major concern. The study aimed at determining variability of ground water levels in Ruiru location. A combination of convenience and random sampling were used to sample 384 respondents using a structured questionnaire. A GPS was used to locate sampling points while a dipper measured groundwater levels. Historical monthly rainfall data (1984-2014) for three stations and Monthly rainfall data (2012-2014) for one station was used for analysis. Monthly groundwater levels data for a monitoring borehole in Murera (2012-2014) was obtained from the Water Resources Management Authority (WRMA) Kiambu office. Data was analysed using Microsoft office Excel, trend software, WINKS SDA 7 and wavelet analysis using matlab. Statistical analysis was done using linear regression and Mann-Kendall. Groundwater recharge was estimated using the water-table fluctuation (WTF) method. There was an insignificant increase in trend in the three stations while high power spectrum was observed within the band of 2-5 years. Rainfall variability showed an impact on groundwater levels as groundwater levels were low 37.2m from the ground level during the dry season when rainfall was 20.7mm and high27.3m from the ground level during the wet season when rainfall was 644.4mm. Estimated recharge for 2012-2014 period ranged from an overdraw of 22mm to 9mm. Rainfall variability showed an impact on water supply systems as 75% of respondents experienced low water supply during drought and relatively higher supply during the wet season.75% of the respondents felt that rainfall affected groundwater quantity and supply. It is recommended that more boreholes be monitored to provide sufficient data for proper assessment and management of groundwater resources.