Estimating Hydraulic Properties of Alluvial Sand Aquifer in Motloutse River course, Eastern Botswana

A single layered alluvial aquifer in Botswana along the Motloutse River catchment was studied to estimate its hydraulic properties. Ground Penetrating Radar Survey (GPR) was used to determine the thickness and porosity of the aquifer. Specific yield of the aquifer was determined in the laboratory. The hydraulic conductivity of the riverbed sediments were estimated using the Alyamani-Sen empirical formula and the hydraulic conductivity of the river bank sediment was measured using the slug test. Geologically, the area is consists of alluvial deposits overlying granite, which is the bed rock of the area. The geophysical survey, GPR, provided information on the range of the thickness of the alluvium (9 – 12m) and also the porosity of the sediments (40%). The laboratory test resulted in an average specific yield of 13.68% for the riverbed sediments and 8.84% for the river bank sediments. A slug test performed in the riverbank yielded estimates of hydraulic conductivity of 26.43m/day. An average hydraulic conductivity value of 160m/day for the riverbed sediments was determined using the Alyamani-Sen formula. This difference in the hydraulic properties of the riverbed and the riverbank sediments is likely to be a result of sediment heterogeneity as more fine grained sediments is found together with sand in the riverbank sediments. These combined hydraulic properties estimation using empirical formulas, geophysical survey, laboratory tests, and the slug test highly improved the understanding of the hydrologic properties of the single layered alluvial aquifer system in the Motloutse River catchment. In the same area, groundwater resource modelling can be done using these aquifer parameters to determine the groundwater potential of the aquifer

Impacts of Treated Wastewater on the Surface Water and Groundwater Quality: A Case Study in North East Gaborone, Botswana

This study was conducted in the Notwane catchment where the capital city of Botswana, Gaborone is located. Botswana having unreliable rainfalls and Gaborone having shortage supply of water for drinking, this study was initiated with the aim of investigating alternative sources in this part of the country. Even though treated wastewater is available in the studied area, this water is not much utilized at present. The objective of the research is to investigate the impact of treated wastewater on the quality of surface water and groundwater in the north east of Gaborone, so that this water can be utilized for different purposes including as a source for groundwater recharge. The research area is located near Gaborone in south east district within Notwane catchment, which is a tributary to the Limpopo River, having an area of about 3 000 sq. kms. For this purpose forty-one surface water samples, one treated wastewater sample and fifteen groundwater samples were collected from different parts of the study area. All the water samples were analysed for major cations (Ca2+, Mg2+, K+, Na+ and Li+), anions (HCO3-, Cl-, SO42-, NO3-, F-, PO43- and CO32- ) and some trace elements (As, Ba, Cd, Co, Cr, Cu, Fe, Mn, Pb, Ni and Zn). For all the water samples alkalinity and hardness were determined using AquaChem software. Simple descriptive statistical method was utilized for the analyses of the water chemistry data. AquaChem and Suffer software’s were also used for analyses the water chemistry data. The surface water range from slightly alkaline to very hard whereas the treated wastewater is slightly alkaline to hard and groundwater is slightly acidic to very hard.In all the waters, surface water, treated wastewater and groundwater based on the mean values of the chemical parameters, the cations were in the order of abundance as Na+> Ca2+> Mg2+> K+> Li+. Surface water anions were in the order of abundance as HCO3- >Cl- > SO42- > NO3- > PO43- > F- >CO32-, treated wastewater as HCO3- >Cl- > NO3- > SO42- > PO43- > F- > CO32- while in the groundwater the anions reveal order of abundance as Cl- > HCO3- > SO42- > NO3- > CO32- > F- > PO43-. Based on the mean values of the chemical parameters in the surface water, the analyzed trace elements were in the order of abundance as Ni > Fe >Pb> Ba > Zn >Mn> Cd > As > Co > Cr > Cu, in the treated water Ni > Ba > Zn >Pb> Fe > Cd >Mn> As > Co > Cr and Cu having equal concentration (0 mg/l) while in the groundwater the analyzed trace element reveal order of abundance as Ni >Pb> Ba >Mn> Zn > Fe > Cd > As > Cu > Co > Cr. The results of the hydrochemical analyses of all the waters disclose that the groundwater chemistry is highly controlled by rock-water interaction and anthropogenic activities in the catchment than the chemistry of surface water and treated wastewater. The analysed cations for surface water and treated wastewater satisfy the standard of both WHO and Botswana Bureau of Standards whereas in the groundwater the cations are highly above the recommended limits of the standards set by both WHO and Botswana Bureau of Standards with the exception of lithium and potassium. The analysed anions for surface water and treated wastewater fulfil the standard of both WHO and Botswana Bureau of Standards whereas in the groundwater the concentration of Cl and NO3 were above the standards set by both WHO and Botswana Bureau of Standards. In the analysed trace elements for all the waters, almost all samples met the trace element standards set by both WHO and Botswana Bureau of Standards with the exception of nickel and lead in surface water, treated wastewater and groundwater. The overall chemical analyses of the water chemistry revealed that treated wastewater quality does not have any significant harm to both surface and groundwater quality; therefore it can be used as a source of recharge to the aquifers in the catchment

The 1950-1998 warm ENSO events and regional implications to river flow variability in Southern Africa

The variability of annual river runoff and its possible association with the 1950-1998 seasonal El Niño/Southern Oscillation (ENSO) is investigated in 502 rivers gauged in 9 countries of the Southern African region. We found some evidence of possible links between available surface water resources in terms of mean annual runoff and warm ENSO events. This was revealed by the existence of strong and nearly-strong positive linear correlation between annual discharges and the warm seasonal ENSO indices explained by the sea level pressure (SLP) data. Of the 502 rivers we considered, 150 rivers exhibit strong positive correlation between the December to February quarter ENSO indices and the annual runoff – with 25% of the variance in annual runoff being accounted for by the warm ENSO events. A relatively weaker positive correlation also occurred in 174 rivers we considered. The strong positive correlation occurs in parts of Zambia, Namibia, Mozambique and the lowveld in South Africa. In these parts of Southern Africa, there is evidence of a general decline in annual runoff after the mid-1970s compared to the period before it. These revelations are explored and are found to be partly explained by the high frequency of drought-related warm ENSO phenomena that occurred during the same period. Water SA Vol.32 (4) 2006: pp.459-46

Strengthening horticultural innovation systems for adaptation to effects of urbanisation and climate variability in peri-urban areas

The significance of urban agriculture is increasingly being recognised across the globe. Urban agriculture’s contribution to food security and poverty reduction, especially for the urban poor, has received increasing attention in urban policy discourses (Satterthwaite et al. in Adapting to climate change in Urban areas; the possibilities and constraints in low- and middle-income countries. IIED, London, 2007; Mutonodzo in Agriculture in urban planning: generating livelihoods and food security. Earthscan, London, 2009; Mkwambisi in Agriculture in urban planning: generating livelihoods and food security. Earthscan, London, Mkwambisi 2009). The impacts of climate change, climate variability and urban growth reduce the benefits derived from agro ecosystem services in peri-urban areas in most developing countries. Peri-urban areas play a significant role in providing ~80% of the vegetables consumed in urban areas of Malawi. However, the vegetable production is dependent on stream water or residual moisture from wetlands, which are being affected by climate change. This study investigated the viability of multi-stakeholder experimentation with sustainable technologies for improving vegetable production in a peri-urban setting experiencing water shortages due to climate change and variability in the Mulanje district in Southern Malawi. Using a participatory action research (PAR) approach, farmers, researchers, extensionists and village leaders worked together to source, test and evaluate various different horticultural production practices. Over a two-year period, they experimented with technologies such as bag (vertical) gardening, differential use of manure and fertiliser, new crops and crop varieties, seed bed preparation techniques and judicial use of pesticides. Those practices identified as successful in 2011 were replicated in 2012 for further evaluation. In general, the study found considerable improvements in vegetable production resulting from the improved agronomic practices. Further, many farmers found bag gardening more convenient due to reduced irrigation requirements, lower labor demands, all year round seasonal production, ease of access and crop security. Improved quality of produce, earlier harvest and increased total number of harvests of leafy vegetables due to manure incorporation, use of improved varieties and high yields in general were among other advantages that were realised. In addition, the technologies promoted minimal use of chemicals, which resulted in reduced seepage of inputs, thereby maintaining agro-ecosystem health. Most communities in the area have adopted the technologies as strategies for climate change adaptation. Scaling up these practices can therefore improve vegetable supply challenges arising from urbanisation, climate change and variability while reducing impacts on agro-ecosystem services