Contact Artefacts
please if you have any comments or more information regarding this record.
Menu
HomeUpfront
Now Up
Books
Towns
Structures
People
Firms
Lexicon
Churchill Dam and Water Scheme
Humansdorp district, Eastern Cape
Contact Artefacts | MenuHomeUpfront Now Up Books Towns Structures People Firms Lexicon | Churchill Dam and Water Scheme | ||
Click to view large map Coordinates: | Also called Kromme Dam Located 110km west of the town on the Kromme (or Krom) River. It is the first multiple-arched dam structure built in South Africa (Freeman 1964:67). In 1957 the locally sourced aggregate used in the concrete was discovered to have expansion properties and the buttresses showed cracks. Although not considered dangerous they were strengthened to the sectional dimensions previously allowed for in the original design to cater for a possible increase of the dam wall height, although the height of the wall was not increased, there not being a need for additional water supply at that time (See also Wikipedia). THE KROMME RIVER DAM The most spectacular construction of the whole [Kromme River Water] scheme, however, is that of the dam wall. This wall is a reinforced concrete structure of the multiple-arch type, being designed as a series of inclined arches between buttresses. Constructionally, the wall comprises 10 buttresses of a pyramid shape and two abutments, with 11 arches. The arches are inclined downstream from the bottom of the dam at an angle of 60° to the horizontal so that the resultant of the pressure against the wall has sufficient downward direction to prevent any movement of the buttresses in the foundations. The maximum pressure which will occur on the foundations of the buttresses is calculated to be 14 tons [14 tonnes] to the square foot [0,09m2]. On a plane at right angles to the upstream face each arch is circular in section, and the radius of the upstream face is 34 - 64 ft. [13,8m - 27,6m]. The arches are 10 ft. [3,0m] thick at the bottom and 6 ft. [1,8m] thick at the top. Concrete mixtures to be used are as follows: Abutments and buttresses, 1 : 3: 6; lightly reinforced arches, 1 : 2+1/2: 5. There are a number of interesting features in the construction of the wall. The arches, for instance, are to be cast as separate units from the buttresses, and the only connecting link between them will be a tongue or continuous strip of copper embedded in bitumen. This strip serves as a water-sealing medium at the joints between the arches and buttresses. The buttresses are self-supporting, being linked together only by a lightly constructed roadway supported by a light reinforced concrete arch rib. In the river bed itself are seven buttresses, with six overflow arch sections spanning between them. Between each of these buttresses at the downstream end or toe, a gravity section wall is to be built. It will be 25 ft. [7,5m] high. Its purpose is to form a stilling pond into which the flood waters, pouring over the six arches, will discharge. This pond will decrease as far as is possible the terrific scouring effect which this falling water would otherwise have. In addition, within the stilling pond and parallel to the buttresses are to be built two 10 ft.- [3,0m] high training walls. These will serve to confine the water, after falling, into a central channel away from the buttresses, which they will consequently protect from scour and the vibration set up by turbulence in the stilling pond. To make further provision for dealing with flood waters, a spillway channel 40 ft. [12,0m] wide is to be constructed on the left bank of the river. A sluice gate 25 ft. [7,5m] in height will be incorporated in the channel. Built into the upstream side of the wall there will be a circular hollow concrete tower with five draw-off pipes radiating at various levels off a central down pipe. The draw-off pipes are fitted with screens. The purpose of these draw-off pipes is to enable the top layer of water to be drawn off, whatever the level of the water in the dam, and to reject, if necessary, the water that has not been subject to the direct rays of the sun. A 3-ft. [0,9m] scour pipe is to be included in the tower. Its purpose will be to remove any silt that may deposit around the tower, and also, during periods of flood, to run to waste water unfit for use by reason of long storage. The normal depth of water at the wall will be 120 ft. [36,0m]. In times of flood it will be 130 ft. [39,0m]. [PWSA November 1940 Vol V No 25:13+17]. References:
|
|
