Sunday, May 21, 2017

Tokwe-Mukosi Facts and Figures
By Special Correspondent

Tokwe Mukosi Dam is located at the confluence of the Tokwe and Mukosi rivers, and the dam straddles the boundary of Chivi and Masvingo South districts in Masvingo Province.

It is 75km South of Masvingo and access to the site is via Ngundu – Triangle Road. From Ngundu, one travels about 16 km towards Triangle and then turns left to reach the dam site about 12km away.

With a height of 89,2m and storage of 1,8 billion cubic metres of water, it is the highest and the largest inland water body in Zimbabwe.

The main purpose of the dam is for irrigation and hydro-power generation. Tokwe Mukosi Dam is designed as a rock fill dam with an upstream concrete face, the first dam of this type in Zimbabwe.

Spillway arrangements comprise of two drop inlet structures, one on each bank, with six meter diameter discharge tunnels all excavated into the rock of the abutments.

The outlet works consist of an upstream intake structure and a six meter diameter pressure tunnel which is connected to a gate shaft immediately downstream of the crest of the dam.

From the gate shaft, two by two metre diameter steel pipes lead through a dry tunnel to the valve house downstream of the dam.

The outlet tunnel served as a diversion tunnel during construction of the dam. There is an upstream coffer-dam which was designed as a masonry arch structure 15 meter high.

There are five Saddle Dams situated on the right bank. The dams are zoned earthfill structures with a total embankment volume of 1 100 000m3.

On the fifth saddle dam, an auxiliary spillway is provided for. Hydro-electric power generating facilities shall be installed on the dam with a maximum generating capacity of 15MW.

Construction period

The contract commenced in April 1998 with a planned construction period of four years stretching from 1998 to 2002.

However, works were suspended in 1999 due to shortage of funds. The project then went through start-stop phases from 2001 to 2005.

Construction then commenced in May 2011 under the current Addenda with plans to complete the project in November 2013 and plans to start impounding water in November 2013.

Due to funding constraints, the project went through some suspension delays but the Government of Zimbabwe cleared all outstanding arrears to the contractor by 11 October 2016.

All critical works were completed in December 2016 and the dam started impounding water during the 2016/2017 rainy season.

As at 17 May 2017, the dam was about 72,38 percent full with a capacity of about 1,303 billion cubic metres.

The Zimbabwean Government wholly funded the construction of the Tokwe-Mukosi Dam.

The dam was primarily conceived to provide irrigation water to the southeast Lowveld and particularly to the Tokwe-Runde-Mutirikwi areas.

An estimated 25 000 hectares of irrigated land is envisaged for establishment with the consequential benefits of increased employment and additional agricultural production.

The harnessed water for irrigation will enable the expansion of commercial sugar plantations to support irrigation schemes for commercial, A2 and A1 farmers.

The Tokwe Mukosi dam wall was designed with the potential of generating approximately 15 megawatts of power if the peak power facility concept is considered using water released for irrigation.

The power generated will be sold to Zimbabwe Electricity Distribution and Transmission Company (ZEDTC) and also used to power the anticipated projects of fisheries, hotels and lodges as the area is developed into a tourism resort. Uptake agreements may be negotiated with mining companies like Renco mine which is in the vicinity of the project.

Other possibilities for the dam include:
l cages fish farming in the dam,

l pond fish farming outside the dam,

l kapenta fisheries.

l large scale crocodile project.

The dam can contribute significantly in eco-tourism projects around the reservoir, these include:

l Self-catering chalets,

l Hotel,

l Conference centre and casino

l Cable car,

l Boating facilities, and

l Game park

l Museum for the construction of the project

l Angling

Dam embankment

The total quantity of rock placed is about 3 million m3. The outlet works consist of hydro-electro-mechanical equipment to operate the gates and also the electrification of the gate house.

Testing of the hydro-electro-mechanical equipment was done in January 2017 and the equipment was found to be operating properly.

There are two drop inlet spillways, one on the left bank and the other one on the right bank.

The total discharge of the two spillways is 1 090 m3/second. There are five zoned earthfill saddle dams all located on the right bank side of the main dam.

There are crest parapet walls which incorporates finishes such as concrete paving of the dam crest driveway and handrails below the downstream parapet walls. Plans for the construction of the powerhouse have kick-started with the commencement of excavation works at the site of the power plant.

This work was awarded to the contractor for the main dam so that liability of the existing structures in the case of any damages that can arise as a result of the blasting that will be carried out still remains with them.

A plunge pool to protect the downstream of the dam wall was constructed. A total 3 425 affected families and their belongings were moved from the dam basin and resettled at Chingwizi on a temporary basis.

They have since moved from the temporary camp to permanent resettlement plots where each family was allocated four hectares of irrigable land.

Compensation amounting to US$9 million is still outstanding for some of the resettled families. There are plans to assist the resettled families with land clearing for them to carry out their agricultural activities.

The construction of the Tokwe Mukosi is a success story and water is now abundantly available for irrigation development downstream and eco-tourism around the dam.

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