Sea Water Intrusion and Surface Water Salinity and Its Influence on Irrigation Water Quality in Ramisi Area, Kenya

摘要

Cane growing is one of the major economic activities in Ramisi, Kwale County besides tourisms and fishing. Although Ramisi Sugar Factory has been defunct for long previously, it has been reinstated and now christened Kwale International Sugar Company Limited (KISCOL). Coast region experience erratic rainfall patterns and limited agricultural land ownership therefore rain fed agriculture is not suitable. The major rivers to supplement experienced unpredictable rainfall patterns in the region are River Ramisi and Mkurumudzi. However, river Ramisi is saline, highly mineralized and unsuitable for domestic and agricultural use according to this study. The river is also affected by seawater intrusion during high tides. KISCOL drilled 37 boreholes to bridge the water demand gap for its operations but the water quality is doubtful due to intrusion effects. The aim of the study was to determine the suitability of water sources in Ramisi in terms of salinity and contaminant levels, risk of salt water intrusion and microbial load. Water samples were purposefully collected from drilled boreholes, River Ramisi and Mkurumudzi then analyzed for organic constituent parameters (pH, Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Dissolved Oxygen (DO) and electrical conductivity). The Physical parameters included; (Turbidity, total alkalinity, total hardness, calcium hardness, magnesium hardness, chlorides and salinity, free carbon dioxide, sulphates, metals) and microbial load using Standard Methods for the Examination of Water and Wastewater quality (21st Edition) at the Kwale Water and Sewerage Company laboratories in Kwale County, and at the Coast Water Services Board laboratories in Mombasa County. The pH of the water sources ranged from 6.5 to 8.5 with exceeding limits for conductivity, chlorides, TDS, turbidity (25 NTU) and TDS (1,237.6667 mg/l). Magnesium, Iron, Sodium and Potassium and nutrients were below the permissible levels for irrigation water. Thus river Mkurumudzi and groundwater sources are not at risk of sea water intrusion, but river Ramisi is suffering from the effects of sea water intrusion during high tides and is unsuitable for cane irrigation and probably any other crop. Most surface water sources were contaminated with total coliforms including E. coli hence not suitable for domestic use.