- ItemUsing unsupported lead-210 measurements to investigate soil erosion and sediment delivery in a small Zambian catchment(Elsevier, 2002) Sichingabula, Henry; Walling, D.E.; Collins, A.L.Traditional techniques used to assemble information on rates of erosion and soil redistribution possess many important limitations. As a result, the use of environmental radionuclides, and more particularly 137Cs measurements, has attracted increasing attention in recent years as a means of obtaining spatially distributed information on rates of erosion and deposition. The application of the 137Cs approach is, however, hampered in some areas of the world where 137Cs inventories are low and the low concentrations of 137Cs found in soils and sediments cause problems for laboratory analysis. These problems will increase as time progresses due to the radioactive decay of the existing inventory, most of which was deposited as fallout ca. 40 years ago. This contribution explores the potential for using another fallout radionuclide, namely unsupported 210Pb, as an alternative to 137Cs, in the small (63 km2) Upper Kaleya catchment in southern Zambia where 137Cs inventories are already very low. The approach employed with unsupported 210Pb is similar to that used for 137Cs, although the essentially constant fallout of unsupported 210Pb through time means that the resulting estimates of erosion and soil redistribution rates reflect a longer period of time (ca. 100 years rather than ca. 40 years). The estimates of erosion and deposition rates derived from the unsupported 210Pb measurements are used to construct typical sediment budgets for the three main land-use types in the Upper Kaleya catchment, namely, commercial cultivation, communal cultivation and bush grazing. The results obtained from the unsupported 210Pb are compared with equivalent results based on 137Cs measurements provided by a previous investigation undertaken in the study catchment. The two sets of results are highly consistent. The study reported confirms the viability of using unsupported 210Pb as an alternative to 137Cs in this environment and demonstrates that conjunctive use of both radionuclides can provide additional information on the erosional history of a study area.
- ItemProblems of sedimentation in small dams in Zambia(Human Impact on Erosion and Sedimentation, 1997) Sichingabula, HenryAn inventory of small dams in Zambia and the results of a preliminary analysis of sediment loads for rivers and reservoirs are reported. A regression approach was used to determine relationships between drainage area and sediment load for 21 rivers based on available sediment concentration and discharge data. The resulting regression equation was applied to the drainage areas of 66 small dams located in Southern Province and rates of sediment input to the reservoirs were computed. By assuming 95% trap efficiency for sediment by the dams, the expected useful life of the reservoirs was also calculated. Calculated annual rates of sedimentation in small dams were found to range from 2 to 183 m3 year1 with a mean of 24.6 m3 year1. The estimates of reservoir useful life ranged from 200 tp 5100 years with a mean of 7314 years. Anthropogenic factors contributing to sediment generation and sedimentation in. reservoirs, community participation in dam construction and rehabilitation efforts together with conservation measures embarked on in the country are discussed. Qualitatively, it is concluded that sedimentation in the dams of Southern Province is serious. This calls for detailed quantitative research to assess the problem and to find ways of minimizing adverse impacts of soil erosion on environment and society.
- ItemSuspended sediment transport characteristics of upper Kaleya river,Southern Zambia(2000) Sichingabula, Henry Walling, D.E. Collins, A.L. Leeks, Graham G.L.Soil erosion has many negative impacts on agriculture and other land related activities and so there is an urgent need to find ways of controlling it. In a bid to increase the understanding of soil erosion and sediment transport processes in Zambia, a project, which was funded by the UK Department for International Development, was conducted in the Upper Kaleya River catchment, southern Zambia, between 1997 and 2000. Being primarily concerned with sediment budgeting, this project necessarily involved the collection of discharge and suspended sediment load data for estimating sediment yields from the study river. This paper reports the suspended sediment transport characteristics of Upper Kaleya River during the study period. Analysis of the data collected at the study catchment outlet, at Roadbridge, revealed that discharge ranged from zero, during some dry season months, to 3.65 m3 s-1, with a daily mean discharge of 0.406 m3 s-1. The corresponding suspended sediment loads ranged from zero to 253.9 tonnes, with a mean of 3.15 tonnes per day. Magnitude-frequency analysis revealed that the flow responsible for transporting most of the suspended sediment load was 1.44 m3 s-1. This discharge represented 1.5 % of the time. During the study period, the total cumulative discharge was estimated at 34.8 million m3, whilst the total suspended sediment load was estimated at 3,130 tonnes. It is concluded that, though the Upper Kaleya River catchment is small, measured discharge and suspended sediment fluxes are reasonably high. Ways of controlling soil loss and of improving water resource protection should therefore be encouraged among the local farmers. There is also an urgent need to conduct this type of research in larger catchments in Zambia and in southern Africa region in order that national and regional sediment-related control measures can be designed and implemented. KEY WORDS: Catchment, effective discharge, magnitude-frequency analysis, river discharge, soil erosion, suspended sediment load.
- ItemSpecial study on sediment discharge and Its consequences (SedSS)(United Nations Development Programme/Global Environment Facility (UNDP/GEF), 1999) Sichingabula, HenryLake Tanganyika is among Zambia's important fisheries which require protection from adverse impacts. Sedimentation is one of the threats to Lake Tanganyika's biodiversity. This is because deposition of sediment clogs streams and reduces their capacities. Pollution by sediment is also one of the major factors causing deterioration in quality of streams and lakes. The sediment deposited into streams, lakes and reservoirs destroys the habitat for fish and other species. In aquatic environments, sediment impairs the dissolved oxygen balance and obscures the light needed for aquatic growth, both of which are detrimental to aquatic life forms. Additionally, heavier sediment particles blanket fish spawning areas and cover food supplies for many species. Pesticides and nutrients origination from agricultural lands are carried off the land by sediment in surface runoff and add to the pollution of downstream waters. For example, phosphates are adsorbed by soil colloids and move into streams and lakes through erosion of soil particles on which it is adsorbed. Nitrogen fertilisers together with phosphorus are the major cause of eutrophication in lakes and rivers which is detrimental to aquatic species. Therefore, the prevention of soil erosion by good conservation practices are the most efficient means of controlling pollution from agricultural lands. The physical characteristics of Lake Tanganyika basin are to a large extent controlled by the geology which is dominated by meta-quartzites of Precambrian ages. These rocks with the high rainfall regime experienced in the area have given rise to the high leached sandveldt soils which characterise the plateau area. These features of the physical environment in the lake Tanganyika basin are discussed in detail. This report documents the activities of the Zambia Special Sediment Study undertaken in almost a period of one year. Methods of data collection an errors inherent in methods used are also discussed. The determination of volumes of discharge and sediment deposited in the lake employed on various statistical models in the development of rating curves. The models selected were tested for accuracy before they were applied to monitored water level data. The study found that mean flow discharges on rivers draining into Lake Tanganyika ranged from 1.426 m3 s-1 on Izi River to 98.563 m3 s-1 on Lufubu River. The lowest and maximum discharges ranged from 0.183 m3 s-1 on Lucheche River to 346.68 m3 s-1 per day on Lufubu River. Similarly, quantities of clastic suspended sediment deposited by the five rivers into the lake between September, 1998 and May, 1999 were found to range from 0.082 tonnes on Kalambo River to 1,539.634 tonnes per day on Lufubu River. The mean values of sediment deposited into Lake Tanganyika were found to range from 1.248 tonnes on Izi River to 208.603 tonnes per day on Lufubu River. Magnitude frequency analysis was used in the determination of the flow ranges which transport the most load in a single year. The effective discharge on the studied rivers was variable ranging from 0.78 m3 s-1 on Izi River to 258 m3 s-1 on the Lufubu River. The durations of these class-based effective discharges were found to range from 2.1% corresponding to the highest discharge, to 54.5% of the time on Izi River where the lowest event transported the most load. The sediment-discharge regimes for rivers in southern Lake Tanganyika basin were characterised by a uniform histogram having a well defined mode and a relatively frequent effective discharge. This was exemplified by Lucheche River. In cases where the regime in which the lower level flows were the effective discharge this was exemplified by Lunzua River
- ItemOccurence , severity and magnitude of hydrological drought in Zambia :impacts and implications(1999) Sichingabula, HenryPersistent occurrence of drought under increasing water supply demands for municipalities and agriculture, and under increased threat of global warming, requires increased understanding of drought characteristics and sustainable use of water resources. Using the theory of runs, several hydroiogical drought parameters of frequency of occurrence, run length, magnitude and run intensity, were investigated for the Kafue and Zambezi rivers. Objectives were to (a) determine magnitude-frequency characteristics of hydroiogical droughts; (b) determine some drought run parameters and frequency of their occurrence; and (c) propose a new approach for increasing Zambia's utilization of its water resources without jeopardizing international relations with neighbouring countries. Better understanding of droughts and assessment of Zambia's present and future water requirements will enable planners and decision makers to bring increased economic benefits to citizens. Zambia's drought and water scarcity problems are outlined and linked to some proposed regional water projects designed to divert water from the Zambezi River system. One possible solution to problems of drought and dwindling water levels on Kafue River is proposed.