Qualitative Assessment of Effects of Encroachment on Water Resources of Agba Dam, Ilorin Nigeria

Abstract

The city of Ilorin in Nigeria has experienced high population growth and rapid urbanization. Agba Dam is one of the major sources of potable water in Ilorin, and currently being threatened by anthropogenic induced encroachment activities, with potential for significant derogatory effects on its quality. Therefore, this paper assesses the qualitative impact of encroachment on the water resources regime of Agba Dam, Ilorin, Nigeria. Field survey was carried out to scope proximal anthropogenic activities and to delineate historical as well as current extent of the encroachment area of the dam. Representative water samples were collected from locations within the dam catchment, and subsequently analyzed for alkalinity, dissolved carbondioxide, chloride, total iron, copper, sulphate, colour, calcium, dissolved oxygen and turbidity. In addition, historical physical and chemical data of water samples obtained from the dam were also acquired, and analyzed to determine temporal variation in the quality. The results show a reduction of 0.89 km2 or 63% in the historical buffer boundary of the dam. The values of the measured physico-chemical parameters were generally similar to that obtained for the historical values and therefore suggest limited impact of the anthropogenic activities on the water quality. However, slight increases were observed in the measured concentrations of the alkalinity, dissolved carbondioxide, chloride, iron, copper and sulphate, and this indicates possibilities of water quality alteration, with potential consequences for ecosystem and aquatic life if the trend is unabated.

Is siltation affecting the limnology and gradually eroding the functions of Agba reservoir, Ilorin, Nigeria?—An old tropical African drinking water reservoir

“…The siltation problem in Agba reservoir is discussed in relation to some of the physicochemical and biotic properties of the reservoir, which facilitated its functioning for drinking water supply, artisanal fisheries and tourism and not as an engineering problem. Busari et al (2014) and Oladeji et al (2016) had earlier reported the average siltation rate and reduction in the reservoir storage volume capacity and buffer boundary. Their results are corroborated by the significant reduction in depth at the bed of the reservoir from the original 17.8 m in 1952 to 12.9 m in 2015 recorded in this study.…”

“…Busari et al (2014) reported the siltation in Agba reservoir, Ilorin, Nigeria, and that the average siltation rate of the reservoir is 9180 m 3 /year, resulting in the lake losing 41.67% of its original capacity in its 68‐year history. Similarly, Oladeji et al (2016) noted that a significant reduction of 63% in the historical buffer boundary of the reservoir, which suggests potential impact on the catchment and consequently on the quality of the lake water resources, while Abdus‐Salam et al (2016) reported the sediments of the reservoir showed a large percentage of some metals occurring in the non‐bioavailable and bioavailable fractions, of which the bioavailable fractions could be a source of problem to the reservoir if leached to the water body when the right pH in the reservoir is attained thereby disrupting the limnology and functioning of the reservoir.…”

“…Three sampling stations were selected to reflect areas of human habitation and activities (station A), lacustrine section (station B) and the riverine section (station C) on the reservoir at 250 m intervals (Figure 2). The reservoir maps, grids, grid point coordinates and elevations for the sampling stations were adapted from Busari et al (2014) and Oladeji et al (2016).…”