Assessment of Kamuzu dams impacts on ecology and hydrology of Lilongwe River

Lilongwe River is one of the longest rivers in Malawi having a length approximately 200 km. The River is the major source of water in Lilongwe District in Malawi, supplying water to about 1,100,000 people. The flow regime of the river is the driving force of all aquatic animals living in the river, hence a need to avoid alteration. The regime affects the biological, physical and chemical properties of water and these in turn affects the ecosystem. This study assesses the ecological and hydrological impacts of Kamuzu dam I and Kamuzu dam II on the flow regimes of Lilongwe River. The daily flow data was divided into two series as pre- and post-impact period: 13 years and 43 years respectively. Based on the Indicator of Hydrologic Alteration (IHA), the range of variability in 33 flow parameters was calculated, and the hydrological alteration associated with the operation of dam was quantified. Using the Range of Variation Approach (RVA) method, five groups of IHA parameters were analyzed to see how they have been impacted as a result of construction of the dams by taking advantage of RVA thresholds. Group 5 and group 2 had a high hydrological alteration (>67%) which signals a negative impact on the ecosystem. The overall hydrological alteration of all the 33 parameters grouped into 5 groups was found to be 64% which is within the range of medium alteration (34%-67%). Hydrological assessment shows that the dams have increased annual flow yield at Q90 between the pre-impact period and post-impact period at station 4D4 by 634 %. There was no large floods in the basin within these two periods .On water allocation, demand for water supply and environment during the post-impact period was met, but in terms of irrigation, months of October and November the required demand to meet the potential 800 ha was met in 10months, which made irrigation only possible for 340 ha in the month of October and 45 ha in the month of November; taking maize as a reference crop under furrow irrigation.