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 110 of 153. I I I I I I I I I I I I I I I I I I I 17 Ash (1978) includes a set of curves which give peak discharge for various return periods, and maximum known floods for Australia and the World, as a function of catchment area. Use of these curves requires estimation of the average stream slope. Ash has suggested a rainfall factor to be applied to these curves to adjust the discharges for arid regions. Using the curves and the rainfall factor, the 100 year return period flood at the damsite is estimated to have a peak discharge of 1000 m'ls and the maximum probable flood is estimated to have a discharge of 4000 m'/s. The Bureau of Meteorology (1979) has estimated the maximum probable precipitation (MPP) for two storm durations in the Alice Springs Region. Using the U.S. Thunder Storm Model, the MPP for a 3 hour duration storm is estimated to be 170mm. By transposing recorded storms the MPP for a 12 hour duration is estimated to be 360mm. For the 12hour duration storm, three likely temporal patterns have been supplied. The most critical temporal pattern gives a peak discharge of 4,620 m3 /s. The initial loss rate and the continuing loss rate were both set to zero, in order to get the maximum runoff. A third estimate of the maximum probable flood relied on information from a storm at Rumbalara Siding in February 1976. Rumbalara Siding is approximately l70km south of Alice Springs on the Central Australian Railway. On the 9th of February, following three days of heavy rainfall, a 9am reading of 41Smm was recorded. Because" the temporal pattern for the storm is not available the 24 hour temporal pattern for arid regions in Figure 3.7 of "Australian Rainfall-and Runoff" was used. The one hour unitgraph for the damsite (Figure 8) was converted to a four hour unitgraph using the principle of superposition with the volume of excess rainfall accordingly adjusted. Using the four hour unitgraph and six theoretical excess rainfall periods the probable maximum flood was estimated to be 5,300 m3 /s. Again, the initial and continuing loss rates were set to zero. This report uses the maximum probable flood derived from the maximum probable precipitation estimates.
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