ICT-Based Identification and Characterisation of Small Reservoirs in the Limpopo River Basin in Zimbabwe

Patrick M Bahal Okwibale Mulengera,Emmanuel Manzungu,Jean Marie Kileshye Onema

doi:10.5539/enrr.v2n3p25

Abstract

Semi-arid conditions that prevail in the Limpopo basin in general and Zimbabwe in particular emphasise the importance of water storage. In this respect small reservoirs play a critical role in sustaining rural livelihoods. However, the management of small reservoirs in Zimbabwe is negatively affected by missing or poorly coordinated information relating to such key attributes as location, capacity, and environmental condition. A study was undertaken to identify and characterise small reservoirs in the Limpopo river basin in Zimbabwe. The objective of the study was to identify small reservoirs and characterise them in terms of capacity, and chlorophyll-a and turbidity indices, as proxies for measuring environmental degradation of catchments in which these are located. The study was carried out in Gwanda district that is located in South West Zimbabwe. Identification was done by processing Landsat TM 4-5 images of February-March and April-May 2009, using Geographical Information Systems. Time and cost considerations were the main factors in the selection of the technology and the images that were used. Field inspections were used to validate selected parameters from February to April 2011. A total of 256 small reservoirs, with an estimated total capacity of 17 million m 3 , were identified. The capacities of reservoirs were found to vary widely from around 4,000 m 3 to over 650,000 m 3 . About half (46%) of the small reservoirs were found to be dry by May, just two months after the end of the wet season. Seven reservoirs, which represented 2% of the total number and 3% of the total capacity of reservoirs, were characterised as highly turbid. Twenty-three reservoirs, representing 9% of the total number and 3% of the total capacity of reservoirs, showed signs of environmental degradation in the catchments. The smallest reservoirs were found to be most vulnerable to environmental degradation. The study concluded that Information and Communication Technologies (ICTs) can successfully be used to identify and characterise small reservoirs in the data-poor Limpopo basin in Zimbabwe, and can be used by decentralised water institutions and River Basin Organisations (RBOs) to better manage available water resources for the benefit of rural communities found therein.

Highlights

Small reservoirs are important sources of multiple water uses for rural livelihoods in the Limpopo river basin in general and in Zimbabwe in particular (Manzungu et al, 2009; Senzanje et al, 2008), because of the semi-arid conditions that prevail in the area (Zimbabwe, 1983)
The study concluded that Information and Communication Technologies (ICTs) can successfully be used to identify and characterise small reservoirs in the data-poor Limpopo basin in Zimbabwe, and can be used by decentralised water institutions and River Basin Organisations (RBOs) to better manage available water resources for the benefit of rural communities found therein
Sometimes the management of small reservoirs is left to the discretion of funders of the reservoirs such as Non Governmental Organisations (NGOs), the state-owned District Development Fund (DDF), and local authorities known as rural district councils (RDCs)

Summary

Introduction

Small reservoirs are important sources of multiple water uses (such as domestic, livestock watering, smallholder irrigation, fishing, dip tanks, and brick making) for rural livelihoods in the Limpopo river basin in general and in Zimbabwe in particular (Manzungu et al, 2009; Senzanje et al, 2008), because of the semi-arid conditions that prevail in the area (Zimbabwe, 1983). The contribution of small reservoirs to rural livelihoods in Zimbabwe is threatened by poor management. This is a consequence of missing or poorly coordinated information (Senzanje & Chimbari, 2002) on such key attributes as location, capacity, and environmental condition of the reservoirs. Such information is critical for allocating water between competing water uses as well as protection of water resources. As the planning and development authorities, RDCs should ideally coordinate the establishment and management of small reservoirs. RDCs tend to leave management of small reservoirs to local people, who lack capacity to effectively manage them (Mufute et al, 2008)

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Conclusion