A spatial assessment of stream-flow characteristics and hydrologic alterations, post dam construction in the Manyame catchment, Zimbabwe

The global hydrologic regime has been intensively altered through activities such as dam construction, water abstraction, and inter-basin transfers. This paper uses the Range of Variability Approach (RVA)  and daily stream flow records from nine gauging stations to characterize stream-flow post dam construction in the Manyame catchment, Zimbabwe. We identify which variables continue to be altered, upstream and at different distances downstream, to distinguish sections with the highest  potential for ecological disruption and to understand how hydrological alterations dissipate downstream of dams. Our results indicate that different sections of the same river have different stream-flow  characteristics post dam construction. The most adverse effects of dams were on downstream stretches of the river which were characterized by low flows, extreme low flows and an increased number of zero-flow days. These differences reflect the  operation rules of the Manyame catchment dams. While the change in stream-flow characteristics is  apparent in the 0–10 km range, it is slightly felt in the 11–20 km range and totally disappears at distances >20 km downstream of dams. These changes in stream characteristics, and that damming is only restricted to the upper third of the catchment, make the hydrologic fragmentations in the catchment minor. However, the continued hydrologic alterations post dam construction raise important concerns about the interactions of hydrology with other factors like sediment deposition upstream of dams and climate change. We  recommend that catchment managers target enhancing the natural flow variability of the river instead of meeting target flows.Keywords: damming, range of variability approach, stream-flow characteristic

The application and testing of diatom-based indices of stream water quality in Chinhoyi Town, Zimbabwe

Aquatic ecosystem biomonitoring tools are largely lacking for many developing countries, resulting in adoption of tools developed from other countries/regions. In many instances, however, the applicability of adopted tools to the new system has not been explicitly evaluated. The objective of this study was to test the applicability of foreign diatom-based water quality assessment indices to urban streams in Zimbabwe, with the view of stimulating research to develop improved approaches for assessing ecological integrity of lotic systems in the country. The study evaluated the relationship between measured water quality variables and diatom index scores. The study found a high degree of concordance between water quality variables and diatom index scores. Thus, the indices proved useful in providing an indication of the quality of the investigated waters. This could be attributed to the occurrence of many widely distributed diatom species that have similar environmental tolerances to those recorded elsewhere. Diatom indices which exhibited consistent classifications and strong correlations with water quality variables such as Trophic Index, Saprobic Index, Pampean Diatom Index, Biological Index of Water Quality and Leclercq Index are recommended for use in the country. However, ecological requirements of some diatom species from Zimbabwe need to be clarified and incorporated in a diatom-based water quality assessment protocol unique to the country