Dikgatlhong Dam
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| Dikgatlhong Dam | |
|---|---|
  Dikgatlhong Dam Location of Dikgatlhong Dam in Botswana | |
| Country | Botswana |
| Coordinates | 21°32′56″S 27°58′52″E / 21.549008°S 27.981034°E |
| Purpose | Urban water supply |
| Construction began | March 2008 |
| Opening date | January 2012 |
| Construction cost | $300 million |
| Owner | Government of Botswana |
| Dam and spillways | |
| Type of dam | Earth fill |
| Height | 41 metres (135 ft) |
| Length | 4.6 kilometres (2.9 mi) |
| Spillway type | Concrete ogee |
| Spillway capacity | 11,000 m3/s |
| Reservoir | |
| Total capacity | 4,000,000,000 cubic metres (1.4×1011 cu ft) |
| Maximum length | 20 kilometres (12 mi) |
The Dikgatlhong Dam is a dam near the village of Robelela on the Shashe River in Botswana, completed in December 2011.[1] When full, it holds 400,000,000 cubic metres (1.4×1010 cu ft) of water. The next largest dam in Botswana, the Gaborone Dam, has a capacity of 141,000,000 cubic metres (5.0×109 cu ft).[2]
The dam is located on the Shashe River three kilometers below the confluence with the Tati River, about 55 kilometres (34 mi) northeast of the town of Selebi Phikwe. It is 5 kilometres (3.1 mi) upstream of the Botswana - Zimbabwe border.[3] The project should increase the secure supply of water for Gaborone, Francistown, and towns and villages along the north–south route for the foreseeable future.[1] It will eventually deliver another 3,000 litres (660 imp gal; 790 US gal) per second of raw water delivery to the north–south carrier pipeline.[3] Water will also be fed to the Palapye coalfields and to the proposed 1,200 MW power station at Mmamabula. Project costs for the dam were around P1,134 million (US$300 million).[4] The pipeline would cost another P1,127 million.[5] The reservoir may also attract tourists drawn by wildlife, water sports and local food, if facilities are developed.[6]
Structure
The dam is a zoned earthfill structure, 41 metres (135 ft) high and 4.5 kilometres (2.8 mi) long. The earthworks contain about 3,870,000 cubic metres (137,000,000 cu ft) of material, including 550,000 cubic metres (19,000,000 cu ft) of clay core from borrow pits and 2,460,000 cubic metres (87,000,000 cu ft) of embankment shell obtained from the spillway channel excavation.[2] The quality of available clay was marginal and required careful selection, treatment and quality control. A layer of broken rock riprap 1.5 metres (4 ft 11 in) thick protects the upstream side from wave action, and a layer of less coarse rockfill 0.5 metres (1 ft 8 in) thick protects the downstream side. The rock, and aggregate for concrete production, came from an on-site quarry.[3]
The geology of the reservoir is very variable. A 58 kilometres (36 mi) long grout curtain incorporating 6,700 tonnes of cement was needed to seal against leakage.[7] The main spillway is a concrete ogee structure 200 metres (660 ft) long with energy dissipators, on the upper left flank of the dam about 2 kilometres (1.2 mi) north of the river. There is also a 900 metres (3,000 ft) long auxiliary spillway to handle conditions of extreme flooding.[2] When filled, the reservoir will have backwater reach of about 20 kilometres (12 mi) up river.[7]
A 48 metres (157 ft) high concrete intake tower 7 metres (23 ft) in diameter with five gate openings feeds a 260 metres (850 ft) long steel pipe 3 metres (9.8 ft) in diameter that passes under the dam embankment and then splits to a pump station and a river outlet. A 61 metres (200 ft) steel bridge connects the intake tower to the top of the dam embankment. The project also included building housing and power supply, and upgrading 44 kilometres (27 mi) of road between the villages of Mmadinare and Robelela. As of 2012 the pump station had yet to be built, as had the 75 kilometres (47 mi) long 1.2 metres (3 ft 11 in) pipeline to carry raw water to the existing North-South Carrier Pipeline (NSC), which in turn carries water south to Gaborone.[2] The pipeline will connect to the NSC at the BPT1 break pressure tank at Moralane.[8]