The catchment is located in the North-eastern part of the country and has a total area of 38 937km2. Mazowe catchment lies between the 16.470S (latitude) and the 18.240S (latitude) and between the 30.680E longitude and the 33.000E longitude. The catchment also straddles over three administrative provinces of Mashonaland East and Central as well as Manicaland covering most of the areas which drain into the Mazowe river system. Mazowe catchment borders it to the northwest and South West and to the south by Save catchment.
The catchment is made up of ten sub-catchment Councils namely : Upper Mazowe, Middle Mazowe, Lower Mazowe, Nyagui, Nyadire, Upper Rwenya, Lower Rwenya, Kairezi, Upper and Lower Ruya and has twenty-four (24) hydrological sub-zones.
THE MAZOWE RIVER SYSTEM
The Mazowe river rises fourteen kilometres (14km) north of Harare at an altitude of approximately 530 metres above sea level. It flows in a northerly direction until its confluence with the Murodzi River 59 kilometres downstream. Thereafter it flows in a general north-easterly direction until it crosses the border with Mozambique at an altitude of approximately four hundred metres (400 m) above sea level. The river has a catchment area of 20 774 square kilometres and thus occupies the bulk of the area under consideration.
Hereunder table 2.1 are some of the major rivers that constitute Mazowe catchment.
SURFACE WATER RESOURCES
The geology of Mazowe catchment is primarily crystalline basement rocks that typically have a low primary permeability and low porosity. The groundwater occurrence in the catchment is either structurally controlled or confined to weathered overburden. The average regolith thickness is generally less than 20m (Key, 1989). Groundwater in the regolith is under unconfined conditions and the aquifers are frequently laterally discontinuous and highly heterogeneous. The saprolite that is produced by the chemical weathering of granites can have porosities of between 15-30% and is generally not a suitable aquifer due to low permeabilities (Fetter, 1994).
General depth of boreholes
The depths of boreholes generally range from 30-50m
Water to be released from Hariana Dam with FSC of 3180 ML and a 10% yield of 1367 Ml. There are currently no agricultural commitments at Hariana Estate but 700 Ml can be reserved for irrigation at Hariana Estate. Therefore 667 Ml can be released into Negomo Dam for Kanhukamwe Irrigation Scheme.
To supplement with boreholes. The groundwater potential yield in this area is 40Ml / annum.River flow during the months of January, February and March can be used for supplementary irrigation whilst water in the dam will be reserved for the months April to December.
Marondera will have adequate water being supplied by Rufaro, Nyambuya, Nyakambiri and Wenimbi from year 2005 to year 2015. Dudley dam must be constructed by 2020 to supplement negative water balance.
Nyarerwe river and Spring source will be sufficient sources from 2005 to 2010. Maroro dam must be introduced by 2015 as the former two sources would be insufficient.
Currently Glendale has adequate water supply from Neslav and Mazowe River. There is need for introducing Kandy arch by 2015, and then Kandy Earth, Dundori, Glenegrey, Murodzi, William Laurie and Jumbo by 2020. All these other dams supply Glengrey that is why Glengrey’ s input must not be considered in isolation.
More efficient irrigation approaches and technologies should be adopted. These include:
- Assessing the Irrigation potential of soils in terms of water loss. This includes determining soil texture, moisture retention properties and the slope and then choosing the more water efficient soils.
- Identifying the suitable water saving technology and the efficient production level.
KANHUKAMWE IRRIGATION SCHEMES
The current state of affairs is that there is water supply deficit 143ML. Water use must be cut down from 3 960 ML to 3 200ML.
Mazowe catchment is currently undertaking investigations for dams and water supply stations for the dams and water supply stations as indicated tables 5.10 and 5.11 below.
|Name of Dam||River||District||Sub-catchment||Purpose|
|Mukotwe||Mukotwe||Rushinga||Lower Mazowe||Water supply to Rushinga Chimhanda|
|Ruya||Irrigation in Mount Darwin Rushinga District. Possible water supply to Rushinga Chimhanda.|
|Nyarerwi||Nyarerwi||Nyanga||Kairezi||Water Supply to Nyanga|
|Nyamapanda dam||Nyamapanda||Mudzi||Lower Rwenya||Water supply to Nyamapanda|
|Chesa Causeway||Mupfure||Pfura||Middle Mazowe||Water Supply to Mt. Darwin|
LARGE SCALE MINERS
There are a number of large mines in the catchment such as Trojan, Mazowe, Ashanti, Arcturus and Madziwa. These operations are a threat to water quality due to the wastewater they release into the surface water bodies. The mine dumps from the resultant processing activities can also affect groundwater since most of them are not lined. Some of the dumps are also not properly vegetated hence siltation of nearby streams cannot be ruled out. Most of the mines also have residential houses thus sewage disposal becomes another threat to water quality.
Backyard houses affect surface water quality through surface run-off and potential breaches occur affecting surface water. One such incident occurred at Bindura Nickel Corporation in which the nearby stream was drastically affected by pollutants from the slimes dam.
SMALL SCALE MINES AND STAMP MILLS
There are numerous small scale miners who either mine old dumps, mine works or stamp millers who crush and process ore normally brought in by panners or other small scale miners. Some of these mines include Dericos, Arcadia and Ndunapayi. The dumps form these operations are normally not vegetated and thus allow a lot of silt into the rivers. The methods used to control outflow of mercury and cyanide are at times not adequate thus causing pollution of nearby rivers. Mud and sand dumps are normally sited haphazardly at the site without lining or compacting the surface. Such a set-up has potential to contaminate groundwater through seepage of other metals associated with gold, in most instances.
SCHOOLS AND HOSPITALS
There are several schools such as St Ignatius, Emmanuel and hospitals such as St Elmi which use septic tanks to dispose their sewage and wastewater. The siting of these septic tanks have not been done with considerations to the porosity of the underlying rocks hence contamination of the groundwater is a likely possibility
FUEL SERVICE STATIONS AND WORKSHOPS
There are a number of filling stations in the catchment. Most of the filling stations have underground storage tanks. These tanks have a high potential of polluting the ground water in the event of any of the tanks leaking. These risks are particularly high in those areas where the stations are located in areas of porous rocks.
NEGLECTED MINE DUMPS
There are several mine dumps in the catchment for example the ones at Inyati and Ran mine, which have not been rehabilitated. During rainy periods, the dumps are eroded and their constituent chemicals end up in rivers causing deterioration in water quality. According to the regulations owners of the dumps are supposed to rehabilitate the dumps by planting grass and trees. However, very few mines are complying with these regulations due to a ‘variety of reasons. Some owners say that they do not have enough resources to do what is required of them. Others claim that the vegetation die off and they do not seem to provide the right variety of vegetation.
There are a number of industries such as Glendale Spinners, Bindura Smelting and Refinery. The wastewater from these industries is usually above the stipulated blue range of the waste disposal regulations. If the volumes are too high this can result in a compromise of the water quality in the nearby rivers.
UNLINED SOLID WASTE DUMP SITES
The Local authorities collect waste and dump them at designated sites within their areas. However the sites are not lined and the type of waste in these dumps is not classified. Some of these pollutants may gravitate to the water table thereby polluting groundwater. Furthermore, the waste is not compacted and when the rains come the rubbish would be washed into rivers. People also come to these sites looking for anything that may be of benefit further increasing the chances of the waste to be spread all over the place. This further increases the chances of waste being carried into rivers.
IMPROPER FACILITIES FOR FARM WORKERS
The catchment has numerous farm workers settlements. Most of these settlements are located close to rivers. The workers do not have adequate toilet and bathing facilities such that any people defaecate in nearby bushes and use the nearby river for bathing and doing their laundry. The soap that people use in their washing contains chemicals for example sodium hypochlorite. These activities result in depreciation in water quality and high microbial contamination. Faecal microbial contamination is very high during the rainy season.
LARGE SCALE COMMERCIAL FARMING AREAS
Fertilisers are used intensively within the large-scale commercial sector and to a lesser extent in the small scale farming areas. Nitrogen compounds can be transported in surface runoff. Phosphorous is transported by eroded soils and can become a pollutant when these soils are deposited in water bodies.
Pesticides, herbicides and fungicides are being used in parts of the catchment particularly within the large-scale commercial farming areas. Runoffs from areas where these chemicals are being used transport them into water bodies. Seeping irrigation water may also affect groundwater quality. The impact of pesticides used for agricultural purposes on water quality in Zimbabwe has not yet been investigated.
STREAM BANK CULTIVATION
In the Mutoko and Murehwa areas, people have a culture of gardening such that almost every family owns a garden. However most of these gardens are located close the river or stream. Despite a lot of emphasis by the AGRITEX officials for the garden to be at least 50m from the river, people are still cultivating along stream so as to reduce the distances they will travel during watering. During the rainy season the soil from the gardens together with the fertilisers they apply is washed into the river thereby increasing chances of eutrophication and suspended particles.
SMALL BUSINESS CENTRES
There are a number of small business centres in the catchment for example Chimhanda, Weya, Cross, and Nyamaropa among many others. A number of activities occur at these places including bakeries, brick moulding, fresh vegetable market, second hand clothes market and general trading. Solid waste from all these activities is disposed of on individual basis and no system of monitoring disposal is in place. Numerous Blair latrines characterize the areas, as it is a requirement that each shop has its Blair latrines for personnel and customers. The citing of these latrines has not been done following the type of underlying rocks and it is possible that some of these rocks may be porous thus allowing sewage to seep to the groundwater.