Revisiting Hydrology of Lake Ngami in Botswana

Kurugundla Cn,Buru Jc,Parida Bp

doi:10.4172/2157-7587.1000301

Abstract

Lake Ngami, an integral part of the Okavango Delta in Botswana, is a seasonal shallow lake that depends mostly on spills deriving from Boro River and rarely from Thamalakane River. In essence, the lake water is critical to the local population supporting the fishing industry, farming, livestock and tourism. This work attempts to revisit and to understand the hydrological conditions of the lake, which are of paramount importance for planning and development processes in the lake area. By referring to earlier historical publications and analyzing annual inflow of Okavango River at Mohembo in Botswana from 1932 to 2016, and annual outflow of Lake River to the lake at Mogapelwa from 1974 to 2016, three flooding regimes have been identified for the Lake Ngami namely wet, seasonal and dry. The hydrological data analysis has shown that the Okavango inflow directly influences the Lake River outflow which in turn determines the lake’s three regimes. The findings show that the longest wet phase for the lake was from 1959 to 1972 and that the longest dry phase was from 1980 to 2003. Water depths measured at six accessible cross-sectional points along a distance of 39.3 km at higher water levels in September 2012 showed that the average depth of water in the lake was 3.508 m. Historical observations on the lake dimensions with water are varied. However, in September 2012 the volume of water determined for the lake was 974 Mm3 occupying 277.7 km2. Outflow volumes to the lake via Lake River and water levels in the lake from 1974 to 2016 provide further evidence to explain the lake regimes. Water quality fluctuations in a given year are varied but can be improved through simple treatments such as boiling or chlorination. This study contributes to the understanding of the lake flow regimes and possible water allocations to the users.

Highlights

The Okavango Delta’s head flows originate in the south-eastern Province of Cuando-Cubango in the Angolan highlands as two rivers, namely the Cubango and Cuito
By referring to earlier historical publications and analyzing annual inflow of Okavango River at Mohembo in Botswana from 1932 to 2016, and annual outflow of Lake River to the lake at Mogapelwa from 1974 to 2016, three flooding regimes have been identified for the Lake Ngami namely wet, seasonal and dry
For Lake River at Mogapelwa, the width and depth of the channel cross section at the highest water level was extracted from Department of Water and Sanitation (DWS)-Hydrology data sheet

Summary

Introduction

The Okavango Delta’s head flows originate in the south-eastern Province of Cuando-Cubango in the Angolan highlands as two rivers, namely the Cubango and Cuito. The data comprises water discharges (Q) at Mohembo hydrostation (inflow) on the Okavango River and at Mogapelwa (outflow) hydrostation on the Lake river including water levels (H) at Mogapelwa as well as at Fisheries Camp hydrostation in the Lake Ngami. For Lake River at Mogapelwa, the width and depth of the channel cross section at the highest water level (which was on 11th August 2012) was extracted from DWS-Hydrology data sheet. The gauge zero above msl is used to compute the water levels for Mogapelwa and Fisheries Camp including for six cross sectionals of the lake obtain in September 2012 (Figure 5). The volume of standing water as of September 2012 in the lake was calculated using the formula: V=A × D, Where V=Volume of standing water, A=Total water Area of the lake as of September 2012 and D=Average water Depths for the chosen six cross sections=277.7 × 3.508=974 Mm3 (Table 2)

Results and Discussion

Summary of observations

52 Mm3 in 1974-c

Conclusion