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Pine Creek region surface water resources assessment Vol 1 - Study report Vol 2 - Geotechnical report



Pine Creek region surface water resources assessment Vol 1 - Study report Vol 2 - Geotechnical report


Willing & Partners; Dames & Moore; Earl James & Associates


E-Publications; E-Books; PublicationNT; Report no. 55/1989







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Northern Territory Government

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Report no. 55/1989

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Attribution International 4.0 (CC BY 4.0)

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Northern Territory Government



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Technical Report WRD89055 Viewed at 15:07:05 on 29/07/2010 Page 39 of 45. Due to the preliminary nature of the study, a judicial assessment of potential flood hazard for each final dam could not be done. The PMF was selected based on the following considerations: . the PJl.1F is the largest design flood leading to conservative spillway requirements the design life of the final dams is anticipated to be 5 to 10 years but may be abandoned intact or reutilized for other purposes. This will increase the potential hazard of the dam advances in analysis and data collection of rare flood events means that design standards are regularly under review. Recent trends indicate the magnitude of low frequency design flood estimates are too low in some cases. In conjunction with unknowns such as the greenhouse effect, the preliminary sele..."Iion of the PMF design standard is justifiable. Revisions to the adopted flood standard should be made during the detailed design stage, taking into account conditions that are specific to each darnsite. The PMF was based on estimates of probable maximum precipitation (PMP) derived by the Bulletin 51 Method (Bureau of Meteorology, 1984). This method makes use of rainfall data from the United States with some adjustments to account for Australian conditions. Its application in the study area is limited to catchments of less than 1000 square kilometres and storms of less than six hours duration. The method has corrections for catchment elevation and terrain which effect the efficiency of a storm in producing rainfall. No elevation adjustment was needed for the smdy area. The terrain of most of the final damsite catchments was classified as 'rough' according to the slope criteria set out in the method. PMP estimates were determined for each of the fmal damsites for a range of storm durations. The PMP estimates were employed v.ith the RAFTS models to generate PMF hydrographs. As detailed in Section 11.3, when routed through each dam storage, the PMF hydrograph were instrumental in assessing spillway requirements. 11.3 Recommended Spillway Requirements Spillway requirements were determined by using the fmal damsite RAFTS models to route the PMF through a range of spillway configurations. Spillway crest level was adopted from the yield analysis outlined in Section 10 and spillway length was adjusted over a range from 50 to 300 metres. PMF hydrographs of different durations were routed through each spillway option to determine the critical flood event. The results of the analyses are summarized in Figures 11.1 to 11.3. The criteria to select an appropriate spillway length was subjective, given the preliminary nature of the study. The maximum flow depth over the spill way (defined as the difference between spill way crest level and peak reservoir level) was limited to 4 metres. The corresponding spillway lengths were extracted from Figures 11.1 and 11.3 and compiled in Table 11.2. The performance under PMF conditions of the recommended spillway options are also given in Table 112. PINE CREEK REGION - SURFACE WATER RESOURCES ASSESSMENT Page 22