Alice Springs recreational dam hydrology report project 6
Jackson, D.; Paige, D.
E-Publications; E-Books; PublicationNT; Report no. 12/1979
Northern Territory Government
Report no. 12/1979
Attribution International 4.0 (CC BY 4.0)
Northern Territory Government
Technical Report WRD79012 Viewed at 00:02:46 on 18/02/2010 Page 85 of 153. I I I I I I I I I I I I I I I I I I I I 2 SUMMARY AND CONCLUSION The usefulness of the impoundment for recreation may be judged by area availability. A sailing triangle of total length 2,400 metres would be available for at least 95 percent of the time. This corresponds to a surface area of approximately 75 hectares. This area availability can be expected with the primary spillway level at 594 metres A.H.D. An annual draft of one million kilolitres could be taken from the storage for watering of parks and recreation grounds without significantly effecting the availability of water for recreation. On average the dam would be filled to spill level about three times every year. It is felt that this area availability would satisfactorily meet the proposed recreational uses, such as small craft sailing, canoeing, fishing and swimming. Rapid rises of water levels during floods - as much as 2.5 metres in four hours for the 20 year return period flood - will necessitate careful location of amenities. During the recession limb of flood wave, the water level will drop quickly to the spillway level. Streamflow through Alice Springs would be reduced. If the damis constructed it is expected that on the long term average streamflow volumes will be reduced by 20 percent. On a time basis, flow is reduced by approximately 30 percent. About 40 percent of individual stream flows would be fully retained in the impoundment. These figures refer to flows entering the town in the Todd River only and do not allow for continued inputs from the Charles River and town drainsa Flooding in Alice springs would be reduced. The level of the expected 100 year return period flow would not exceed the level of the present 20 year return period flood. The 50 year return flood would be contained within the banks of the Todd River, except for areas along Leichardt Terrace and South Terrace. A conservative estimate of dam life before complete silting is 120 years. To achieve this life it will be necessary to incorporate a sediment trap immediately upstream of the impoundment. This will trap bed load at an estimated rate of 16,000 tonnes per year. By comparison demand for construction sand in the Alice Springs region is ,currently averaging approximately 53,000 tonnes per year, and hence in most years it should be feasible to completely mine the trap.
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