Civil Engineering Staff Publications

Hydrological impacts of urbanization of two catchments in Harare, Zimbabwe

2026-01-06T01:02:12Z

Hydrological impacts of urbanization of two catchments in Harare, Zimbabwe Gumindoga, Webster; Rientjes, Tom; Shekede, Munyaradzi Davis; Rwasoka, Donald Tendayi; Nhapi, Innocent; Haile, Alemseged Tamiru Abstract: By increased rural-urban migration in many African countries, the assessment of changes in catchment hydrologic responses due to urbanization is critical for water resource planning and management. This paper assesses hydrological impacts of urbanization on two medium-sized Zimbabwean catchments (Mukuvisi and Marimba) for which changes in land cover by urbanization were determined through Landsat Thematic Mapper (TM) images for the years 1986, 1994 and 2008. Impact assessments were done through hydrological modeling by a topographically driven rainfall-runoff model (TOPMODEL). A satellite remote sensing based ASTER 30 metre Digital Elevation Model (DEM) was used to compute the Topographic Index distribution, which is a key input to the model. Results of land cover classification indicated that urban areas increased by more than 600 % in the Mukuvisi catchment and by more than 200 % in the Marimba catchment between 1986 and 2008. Woodlands decreased by more than 40% with a greater decrease in Marimba than Mukuvisi catchment. Simulations using TOPMODEL in Marimba and Mukuvisi catchments indicated streamflow increases of 84.8 % and 73.6 %, respectively, from 1980 to 2010. These increases coincided with decreases in woodlands and increases in urban areas for the same period. The use of satellite remote sensing data to observe urbanization trends in semi-arid catchments and to represent catchment land surface characteristics proved to be effective for rainfall-runoff modeling. Findings of this study are of relevance for many African cities, which are experiencing rapid urbanization but often lack planning and design.

Improved flood estimation model for bridge and culvert design in Zimbabwe

2025-12-14T01:13:22Z

Improved flood estimation model for bridge and culvert design in Zimbabwe Mamombe, L; Tumbare, M. J. Economics and risk minimization in the design of infrastructure that is vulnerable to flood damage often prove to be non-commensurate objectives. To economically minimize the risk of hydraulic failure of this type of infrastructure is a noble design objective. The hydraulic design of bridges and culverts in Zimbabwe is currently hinged on empirical algorithms of flood estimation. In a changing climate and changing land use environment, the current flood estimation method seems to under-estimate the design floods as evidenced by the increasing number of bridges and culverts being overtopped by floods. This paper discusses the several shortcomings of the current method in use and proposes a new consistent but robust computerized method of flood routing based on historical flow data and statistical analysis techniques. The methodological praxis and resultant design software are intended to substantively improve the flood estimation process, producing a more precisely estimated design flood. From the results obtained, the proposed new model is more conservative than the current method used by the Ministry of Transport (MoT) by an average factor of 1.4. At ungauged sites, or at sites where the stream flow data is inadequate in quantity and quality for Flood Frequency Analysis (FFA), it is recommended that a factor of safety of 1.4 be applied to MoT current flood estimates.

Water insecurity in Zimbabwe’s towns and cities: Challenge for institutions

2025-10-25T01:34:31Z

Water insecurity in Zimbabwe’s towns and cities: Challenge for institutions Makurira, H.; Tumbare, M. J. There is widespread concern over water insecurity in most towns and cities in Zimbabwe. Some households have gone for years without receiving water yet most reservoirs supplying such towns or cities have been recording decent storage levels throughout the years. This suggests that the collapse of water service provision in the country is not related to shortage of quality raw water, but indicates dilapidation of water infrastructure due to a combination of lack of maintenance, lack of timely investments in infrastructure and general collapse of the water governance structures. In the absence of reliable and safe water sources, communities resort to unsafe sources of water resulting in increased exposure to diseases. The related collapse of wastewater treatment systems has also resulted in many towns and cities discharging almost untreated sewage into public watercourses. Within these municipalities are institutions that also rely on reliable municipal water supplies. Such institutions include schools, colleges, hospitals, clinics and hotels which house large concentrations of populations at given times. Failure to secure reliable and safe water for such institutions threatens operations and may even expose such populations to diseases related to poor sanitation and hygiene. Institutions are therefore increasingly seeking own secure sources of water with groundwater being the immediate option. This paper supports the development of groundwater sources to improve institutional water security but also recommends that such options should be operated as emergency alternative sources to guarantee water security in the event of failure by traditional sources. However, this should be accompanied by strict monitoring of abstractions and water quality so as to safeguard human and environmental health.

The spatio-temporal variation of the 2014 Tokwe-Mukosi floods: a GIS and remote sensing based approach

2025-10-02T01:15:03Z

The spatio-temporal variation of the 2014 Tokwe-Mukosi floods: a GIS and remote sensing based approach Gumindoga, W; Chikodzi, D; Rwasoka, D; Mutowo, G; Togarepi, S; Dube, T Floods are natural hazards that have always created an unexpected threat to human life and property. When severe floods occur in areas occupied by humans, they can create natural disasters that involve the loss of human life, loss of property and may result in serious disruption to the ongoing activities of urban and rural communities. The unanticipated and incessant heavy rains in 2014 that pounded theTokwe-Mukosidam catchment from late January and March led to flooding of the dam basin affecting villagers in the area. The affected villages were mainly those that had not headed to the call by government to relocate to identified land. This created an emergency situation due to increase in volume of water in the dam reservoir. The increase in volume contributed to flooding of the dam basin, marooning the houses and fields in the upstream and destroying infrastructure. Earth observation techniques and GIS can contribute towards more accurate flood hazard mapping that can be used to assess damage to residential properties, infrastructure and agricultural crops as well as provide information for emergency relief work. The objective of this study was to use remote sensing and Geographic Information Systems to determine the spatial variation of flood hazard in the Tokwe-Mukosi Dam area during and after the 2014 flooding using the (recent launched 2013) 30m Landsat 8 OLI based images via GloVis website (http://glovis.usgs.gov/).A segment map digitizing technique in ILWIS was used to separate the water and non-water areas. Areas occupied by water in the different dates were also determined through histogram analysis. The digitized segment maps was exported as a shapefile in ArcGIS and then over-layed with other important data such as soil type and land cover maps. The land surface characteristics (such as elevation, land cover, and distance from stream network, rivers and road network) were also related with the presence and absence data (flood condition) using a spatial logistic regression in SPSS v17.0. Results indicate that the water inundated area increased by more than 40% from January 2013 (just before the floods) to February 2014 (During the floods) and April 2014 (after the floods). Factors such as elevation, distance from river network had a signification relationship (p<0.05) with flood hazard. Thus the use of remote sensing and statistical techniques can be a valuable tool for flood plain zoning and disaster preparedness for the settlements in the Tokwe-Mukosi Dam area. It can also help to prevent undesirable side effects of the developments and can assist in implementing effective mitigation measures.