Browsing by Author "Makokha, Mary"

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    Groundwater Quality Analyses along Kenyan Coastal Region, Case Study of Kilifi-Kenya
    (International Journal of Environment and Geoinformatics, 2019-04) Makokha, Mary
    The Kenyan coast is a semi-arid region frequently faced with severe water scarcity especially during prolonged drought and a rapid population growth. Groundwater provides 50% of the water demand and most sources are poorly drilled, over-abstracted and abandoned. The aquifers occur in sedimentary formations of fluvial and lacustrine origin. There is a need to have a groundwater monitoring system in place; therefore this study analyses selected physico- chemical and microbial parameters using both laboratory and field methods. Arc-GIS 9.3, SURFER were used to generate thematic maps for some tested parameters. Results indicate pH values within acceptable range of 6.5 – 8.5, though shallow wells in Malindi were acidic, this atrributed to the heavy industries prevalent in the area. Electric conductivity (EC) was above the set standard of 1500μS/m indicating high dissolved ions present especially in Magarini where salt mining is done. Total dissolved solids (TDS) of up to 500mg/L suitable for drinking water was only found during the wet season. Turbidity of less than 5 NTU was established in most areas. Chlorides and salinity levels exceeded 250mg/L pointing to the saltwater intrusion problem that is a challenge along Kenyan coastal aquifers Boreholes and shallow wells had a total hardness ranging from 50mg/L -150mg/L indicating the water was ranging from being slightly hard to hard water. Escheriria coli was present in almost all the boreholes and shallow wells indicating the need to treat water before use. Water Quality index (WQI) calculation indicate that groundwater is unsuitable for human consumption in dry season.
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    Trends in Rainfall and Discharge over Zaaba Sub Catchment, Vihiga County, Kenya
    (Open Access Library Journal, 2024-10) Aholi, Joel Philip; Makokha, Mary; Obiero, Kennedy
    Temporal variation of rainfall has a direct influence on discharge of a river; however, considerable land cover changes through conversion of natural veg etation to agricultural land, settlement and commercial usage like urbanization have led to encroachment into forested, river riparian and other wetland areas therefore altering runoff generation through variation of rates of vegetal inter ception, infiltration, evapotranspiration and surface detention. This study determined rainfall trends and discharge from 1991 to 2020 and factors de termining response of streamflow to rainfall variability in Zaaba river sub catchment in Vihiga County, Western Kenya. Rainfall data was sourced from Kenya Meteorological Department, discharge data was sourced from Water Resources Authority and land cover data was downloaded from USGS website http://www.earthexplorer.usgs.gov/. Trend analysis was determined by Z-Test, p-value and Sen’s slope estimator. Regression analysis determined the correla tion between rainfall and discharge. Data from Key informant interviews, ques tionnaires and Focus Group Discussions was analysed through SPSS by com puting totals and percentages and drawing charts. Rainfall trend analysis at α = 0.05 revealed rainfall was variable at monthly (p-value = 0.037 and Sen’s slope = 0.182), seasonal (Sen’s slope = −0.030 and p-value = 0.043 for MAM and Sen’s slope = 0.136 and p-value = 0.046 for OND) and annual (Sen’s slope = 1.081 and p-value = 0.010) time steps. Discharge trend analysis at α = 0.05 re vealed existence of trend on seasonal (Sen’s slope = 0.51 and p-value = 0.009 for MAM and Sen’s slope = 0.521 and p-value = 0.008 for OND) and annual (Sen’s slope = 0.085 and p-value = 0.001). Regression analysis revealed insig nificant seasonal correlation (MAM and OND with r = −0.124 and 0.067) and annual correlation (r = 0.051). Statistical analysis revealed that major land cover changes were agricultural area that decreased from 50.05% (2001) to 41.07% (2011) and 32.8% (2020) and increased buildup areas from 5.06% (2001) to 9.29% (2011) to 17.68% (2020) attributed to increased population, expansion of urban areas and encroachment into river riparian that decreased from 5.18% (2001) to 1.18% (2011) and 0.87% (2020). These findings would encourage ca pacity building on increasing rainfall trends and take measures to control floods.
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    Urbanization and Hydrological Dynamics: A 22-Year Assessment of Impervious Surface Changes and Runoff in an Urban Watershed
    (Frontiers in Water, 2024-12) Ongaga, Cyrus Omwoyo; Makokha, Mary; Kennedy Obiero; Kipkemoi, Isaac; Diang’a, Justus
    The frequency and intensity of flooding have been increasing in urban watersheds. Urbanization disrupts natural landscapes by replacing vegetated areas with impervious surfaces, reducing infiltration and increasing runoff. The objective of this study was to evaluate the relationship between change in impervious surface area and runoff amount of Mihang’o watershed located in the outskirts of Nairobi for the period 2000–2022. The specific objectives of this study were as follows: To determine the change in the impervious surface area of Mihang’o watershed, the trend of precipitation amount in the watershed, and the trend in runoff amount, a major source of flood water from the watershed. Supervised classification was performed on land satellite (Landsat) images to determine percentages of impervious surface cover for the study period, and linear regression analysis was used to establish the trend. Climate Hazards Group InfraRed Precipitation with Station (CHIRPS) rainfall data were retrieved from Google Earth Engine, then processed to produce monthly and annual rainfall totals, and Mann–Kendall trend tests were used to establish the rainfall trend for the watershed. The Hydrologic Engineering Center’s Hydrologic Modeling System (HEC-HMS) model was used to simulate runoff from the watershed with the rainfall data and impervious surface area percentages as inputs; then, linear regression analysis was performed to establish the runoff trend. The impervious surface area increased by 87.03% from 2.88% (0.49 km2 ) of the total surface area of the watershed in 2000 to 22.21% (3.91 km2 ) in 2022, demonstrating an approximate increment of 3.96% (0.88 km2 ) each year. The Mann–Kendall trend test results (Sen’s slope results [β = 0.832], Kendall’s tau results [τb = 0.146], and p-value [0.625]) confirmed that there is no significant change in rainfall amounts. Runoff increased by 84.75% from 0.18 mm in 2000 to 1.18 mm in 2022; otherwise, an approximate increment of 3.85% (0.045 mm) was evident each year. Besides the impervious surface area, the HEC-HMS model factors in the length of slope, length of reach, soil type, size of subbasins, and longest flow path, thus producing accurate runoff estimations.