A new dam was built in the catchment of the Sabie River, which will serve as a storage facility for a pipeline transfer scheme in Busbuckridge. The project is aimed at supplying bulk raw water for domestic use to the rural and semi-urban population consisting of more than a million people. The dam will also have an environmental impact on the catchment of the Sabie river due to the fact that access runoff can now be released in a controlled manner to ensure supply in the natural riverine environment and in the adjoining Nature reserves. See annexure B5 for construction photo coverage

Locality

The dam was constructed in the Marite river, which is adjacent to the Sabie river in the Mpumalanga region. The dam wall is situated on property registered to be Inyaka 267 KU in the district called Mapulaneng. The co-ordinates were determined to be at S 24° 53' 06" and E 31° 05' 10". This position could be plotted on a 1:50 000 topographical chart of 2431CC Bushbuckridge. See annexure A

Structural Information

The dam consists out of earth filled flank walls on either side of the central trough spillway. The overall length of the structure is 550m whilst the total spillway length measures up to 138m. The spillway crest level is 35m above the lowest draw down level (RL 733,71m). The total volume of earth fill used was 1,4mil m³ against the 330 000m³ concrete used to construct the spillway and tower. See annexure C for detail sketches about wall and outlet works

The design flood level for the dam is 36.6m higher than the lowest draw down level, at 770.30m above mean sea level. The reservoir capacity at full supply level (FSL) is 123mil m³. Design spillway discharge at high flood level is 1300m³/s and during design flood level of 770.3m the discharge should be 610m³/s. A temporary area capacity table was derived from the surveys conveyed and the plans of the dam wall and it was detected to be faulty due to the fact that some alterations were made during the construction of the spillway which was not indicated on the plans. Therefore it is considered to be temporary, until as build surveys are completed to confirm alterations made during construction.

The outlet structure consist out of two 1m diameter sleeve valves plus an additional two 400mm diameter sleeve valves, to release water into the Marite river, which will be monitored at the down stream component X3H011. See annexure A1 for the temporary area capacity table.

Hydrology

The dam is constructed in the Marite river, which is in the catchment of the Sabie river. It is therefore situated in the X3 drainage region adjacent to the Sand and Mac Mac rivers. The catchment area of the dam covers 210km², mainly in the Graskop vicinity. Construction was completed early in 2002 and the first gauge plate reading was already taken on the 2nd February 2002. MR. Ronnie Kasrils opened the dam on the 22 March 2002. See annexure A2 for a map of the drainage region and area of Inyaka dam. Releases or minor spills at Inyaka dam are being measured by a V-crump structure, X3H011, Marite river at Inyaka. The dam and the down stream component are both equipped with electronic data logging equipment, which monitors water levels continuously. (See annexure A3 for electronic generated data) A data collector responsible for data retrieval in the X-Drainage region is downloading the loggers on a monthly basis, however the water bailiff in charge is completing a daily dam return. (Mr. N. Tereblanche). The first date for electronic data capturing is noted to be 16 April 2002 although X3H011 has a well-defined history before this date. (Note. A blank copy of this return is visible in annexure A4.)

Inyaka dam is also equipped with real time communication through which data can be downloaded and used to update the regional website of Mpumalanga. This dam levels and other river levels can be viewed at http://www.dwaf.gov.za/directorates/hydrology/

The dam was designed by the Dept. of Water Affairs and forestry, constructed by it's own construction division and is therefore the property of the Dept. The responsibility for data capturing and maintenance is also one of the Department of Water Affairs and Forestry done by the hydrology division of the Mpumalanga region. Due to the fact that this is a newly constructed dam, an application form for the number allocation of a new hydrological gauging station is submitted in Annexure A5.

Components of Inyaka Dam

All factors that could effect any dam balance calculations are being monitored on site at Inyaka dam. Therefore a fully operational evaporation station was erected right next to the bailiff's office for daily observations. As mentioned earlier is there a down stream component to monitor all outlets and minor spills over the crest of the spillway whilst abstractions for purification are monitored at the water purification plant a mere 15km from the spillway. These components are being discussed as follows:-

Evaporation station The evaporation station consist out of both evaporation tanks used in the Dept. namely the Symons tank and the Class A pan. To calculate dam balances accurately one should not only take evaporation in consideration but also precipitation and for this measurement there is also a standard 127mm diameter rain gauge installed in the evaporation station. This gauge is also being checked on a daily basis and even an additional gauge was erected at a height of 1.5m above ground level to double check rainfall measurements. The station is also equipped with available running water (tap), which can be utilized for refilling and cleaning of the tanks if required. The bailiff is responsible for daily readings and therefore the evaporation station was erected right next to his office within the prescribed confinement. The co-ordinates for this evaporation station are S 24º 53' 24" and E 31º 04' 38". Mr. Tereblanche was provided with the required monthly return forms, which is being updated on a daily basis. After completion this returns are sent through to the regional office at Groblersdal. (Private Bag X 8616; Groblersdal; 0470) Note. An example of this evaporation return is visible in Annexure A6 Photos of the station included in annexure B

Spills and releases into Marite river As mentioned in the beginning of this report is this dam essential to uphold the ecological environment in the Sabie river. Therefore releases from this "reservoir" are almost expected to be rather constant due to the fact that normal flow is now completely contained for storage purposes. This dam was designed with four release valves in the concrete structure of the spillway, which will be utilized to uphold the aquatic environment in the Marite and Sabi rivers. This releases is being monitored down stream of the wall in the Marite river at X3H011; Marite at Inyaka and could be found at the following co-ordinates S 24º 53' 22" and E 31º 05' 27". This station was build long before Inyaka dam and already has a long history of flow record being captured on the flow data bank. This weir was also being upgraded during the construction of Inyaka dam. Some significant changes that were carried out was the changing of the inlet system which was first on the left bank and is now on the opposite, -Access that was created on the right bank to the structure which was at first impossible, -The addition of the new concrete recorder hut which provides better security to loggers and equipment and the raising of the flank walls to increase structure capacity. This station is equipped with electronic data logging equipment and the long-term goal for this station is to incorporate it into the real time data network for easier catchment management. Currently this is not possible due to the fact that vandalism runs high in this area. Vandalism is of such a magnitude that even 22 000 volt overhead electrical cables, which powers Inyaka dam's cranes and all other electrical requirements, was recently stolen to sell as scrap metal. Therefore communication to this station is a long-term goal to see what technology can provide with regard to communication devices with very low power consumption? Note: See annexure A7 for the discharge table for X3H011 and annexure B2 for photo coverage of this station.

Abstractions for human consumption

A purification plant is currently under construction in Bushbuck ridge for the sole purpose of treating water from Inyaka dam for human consumption in the vicinity. Currently water is being pumped from the dam with a temporary pump station which feeds water to the purification plant. This station is situated at the following co-ordinates S 24º 51'16" and E 31º 04' 39". There are no meters at this specific pump station but the water is being pumped into a storage dam at the purification where the quantities are being calculated by a flow meter in the raw water pipe line. Volumes are displayed in cumecs. (See annexure B3 for pictures regarding temporary pump station)

After purification water is distributed into various pipelines, which lead to the surrounding water storage reservoirs. Provision was made for four main pipelines from the plant and each of this lines is equipped with it's own flow meter which indicates volumes in cumecs, pumped through the specific pipeline. It is not certain of the available readings and data up to date but the water bailiff of Inyaka, Mr. Natie Tereblanche was instructed to take all the meter readings at the plant on a daily basis. These meter readings are essential and should be noted on the monthly dam return for accurate dam balance calculations. Hydrological monitoring point numbers should also be allocated to all these mentioned meters. The allocations of these meters are as follows: - Raw water pumped from Inyaka dam into raw storage dam Co-ordinates of meter S 24º 51'56 " and E 31º05' 18" Treated water from plant into pipe line 1-4 feeding reservoirs Co-ordinates of meters 1-4: S 24º 51' 39" and E 31º 05' 19"

Although the construction of this plant is not yet complete and only two pipelines are currently in use, I would recommend the constant monitoring of all four meters to ensure accurate calculation of dam balancing. As mentioned earlier, water is being abstracted with a temporary pumping station. The same flow meters will be utilized to determine abstractions from Inyaka dam even if the original planned abstraction point is erected. The pipeline network is already in place this will only be switched from the currently used pumping station to the new pump station position. See annexure B4 for photo coverage of the various flow meters and purification plant.

Hydro Mpumalanga Groblersdal

24 June 2002