The effect of surface albedo and grain size distribution on eveporation losses in sand dams

Sand dams are very useful in arid and semi arid lands (ASALs) as facilities for water storage and conservation. Soils in ASALs are mainly sandy and major water loss is by evaporation and infiltration. This study investigated the effect of sand media characteristics, specifically surface albedo, grain  size and stratification on water table recession using experimental model. Tanks of 220 litres capacity and 0.9 m depth were set as evaporation  media at the JKUAT weather station in Kenya. Experimental media investigated were; fine ballast, fine sand, coarse sand, in situ sand and stratified combination. Surface albedo were varied by painting top sand media with colours such as white, grey and natural brown sand colour asa control. Albedo were indexed using luminance factor. The study  concluded that evaporation losses are inversely proportional to the albedo of the evaporating surface measured in terms of luminance factor. The relation between water table recession in porous medium and pan evaporation is an exponential decay curve. The study showed that stratification of media have significant influence on water loss particularly, if the overlying material is courser than the underlying layers

Assessment of pollution in Ndarugu river due to runoff and agro-industrial wastewater disposal

River Ndarugu is a tributary of Athi River in Kenya and is one of the main sources of fresh water for domestic use to the villages along the river bank and Nairobi City. It traverses Juja Township in Kiambu County, Central Kenya. During its course through the different agricultural and industrial areas of Gatundu, Gachororo and Juja farms, it receives untreated agro‐industrial waste discharges, effluent from coffee and tea factories, and other agricultural activities in the catchment area. This paper aims at assessing the level of pollution due to these activities. Water samples were collected from seven sampling points during the dry season in July and short wet season in November and December and analysed in situ and at Jomo Kenyatta University Environmental laboratory for eight parameters. These include pH, temperature, electrical conductivity (EC), Turbidity, Nitrogen, Phosphorous, Biochemical oxygen demand (BOD5) and dissolved oxygen (DO).The samples were collected at 15cm depth (to avoid floating materials) and geographical positioning system (GPS) device was used to spatially locate the sampling sites. Samples were taken from upstream and downstream of point and non‐ point sources of pollution. Results indicated that most physical parameters were within the WHO limits for drinking purpose. BOD5 and EC levels increased from 12mg/l to 22mg/l and 55μS/cm to 85μS/cm respectively but DO level decreased from 6.3mg/l to 3.4mg/l moving downstream in dry season. Turbidity was above the allowable limit in both seasons. Nutrient levels were within the limits and no phosphorus was detected. There is need for proper control of wastewater by various techniques, and preliminary treatment of waste discharges prior to effluent disposal. Care should be taken in application of inorganic fertilizers. Management of the watershed is also necessary so as to protect the river from the adverse impacts of agricultural activities and save it from further deterioration.Key words: biochemical oxygen demand, dissolved oxygen, electrical conductivity, pollutio