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

Tongayi Mwedzi,Tinotenda Mangadze,Taurai Bere,Loreen Katiyo,Francis T Mugabe,Courage Bangira,Olga L Kupika

doi:10.4314/wsa.v42i2.03

Abstract

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.

Highlights

Flow is the primary driver of physical habitat conditions in rivers, which in turn is a major determinant of biotic composition (Jiang et al, 2014)
We reported increased zero-flow days, high-pulse duration, high-flow timing and extreme-low-flow duration at sites situated 0–10 km downstream of dams compared to other site categories
Our results indicate that the flow regime at different sections of the Manyame catchment has been altered over the past 49 years post dam construction

Summary

Introduction

Flow is the primary driver of physical habitat conditions in rivers, which in turn is a major determinant of biotic composition (Jiang et al, 2014). For instance, alters important characteristics of the flow regime, i.e., magnitude, frequency, duration, timing (predictability), and the rate of change (flashiness) (Poff et al, 1997; Dudgeon, 2000; Jiang et al, 2014). This results in hydrologic fragmentation (Jiang et al, 2014), habitat fragmentation, conversion of lotic to lentic habitat, degraded water quality, altered sediment transport processes, and changes in timing and duration of floodplain inundation (Pringle et al, 2000). Such changes have an impact on biological communities and the ecological integrity of rivers worldwide

Methods

Results

Discussion

Conclusion