Groundwater Flow and Quality of Coastal Aquifers

Master's Thesis from the year 2017 in the subject Engineering - Civil Engineering, grade: 80.00, , course: Civil Engineering (Environmental and ASAL Option), language: English, abstract: Groundwater is the world's most readily available source of freshwater, hence the importance of aquifers. However, groundwater resources are prone to pollution in the wake of anthropogenic influences, over-exploitation and climate change related activities. Coastal aquifers are faced with added unique challenges of seawater intrusion. The coastal aquifer of Mombasa, home to East Africa's busiest seaport is not an exception to these challenges. This study investigated the groundwater flow, quality and vulnerability to seawater intrusion of the coastal aquifer of Mombasa North Coast. This is a 74.2 km2 region bounded by the Indian Ocean on the East, by creeks on the North and South and high elevated hills on the West. The hydrogeological characteristics, salinity and extent of seawater intrusion of the aquifer were assessed using statistical and geospatial methods. The statistical methods include correlation coefficients, cross plots and Piper plots. GALDIT overlay index was applied in assessing the vulnerability of the aquifer while groundwater flow and solute transport were simulated with the aid of MODFLOW, MT3D and SEAWAT packages. Field data such as static groundwater levels and water quality parameters were collected at pre-monsoon, rainy season, and post-monsoon of 2016. This was followed by laboratory analysis for Na, K, Mg, Ca, Cl, HCO3 and SO4 concentrations in the obtained water samples. The results show the aquifer is shallow and unconfined with groundwater heads ranging from -1 to 33m above mean sea level. The EC and TDS values showed near perfect correlation relationships and were generally high, as over 94% of the water samples exceeded WHO drinking water limit. The groundwater pH was slightly alkaline but could be slightly acidic in the rainy season due to groundwater recharge from rainfall. There is a wide spatial variation in water quality parameters in the aquifer. The groundwater salinity varies with seasons and groundwater recharge heavily influences the salinity of the groundwater. The aquifer largely experiences a moderate impact and moderate vulnerability to seawater intrusion. However, vulnerability is higher in the dry season. Finally, the direction of groundwater flow is predominantly towards the north-eastern and southern part of the study area. In view of the findings made, management and modification of the pumping scheme are recommended to help prevent further deterioration of the groundwater quality.