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 150 of 153. I I I I I I I I I I I I I I I I I I I I 47 In the event of an extended wet period with sustained flows or an overall drop in demand for river sand, another sediment trap somewhere further upstream could be constructed~ 3.6 Downstream Scour 3.6.1 Moveable Bed Computer Model A programme based on an alluvial bed transient model (Ponce, Garcia and Simons, 1979) was written to examine the effects of downstream scour. The model solves the equations of water motion, water continuity and sediment continuity using an implicit finite difference scheme. The equations are solved simultaneously at each time step. The model is one bed level only. the D50 size and account is taken calculated using dimensional and calculates changes in Sediment transport is characterised by is not routed by size fractions. No of armouring phenomena. Roughness is the DarCy-Weisbach friction factor. Hydrographs are divided into a series of discrete steady state flow rates. At the beginning of each steady state flow, a backwater calculation gives the initial depth of flow at each cross-section. The simultaneous finite difference equations are then solved at time increments within the steady flow time period to give flow depth,' energy slope, bed load transport rate and bed elevation at each cross-section. Problems were encounted in the solution algorithm and also in meeting the convergence and stability criteria. Convergence and stability criteria for the model have been estimted using time periods of years and degradation lengths of miles. To meet similar criteria on the Todd River, increments of the order of 5 minutes and SOm are requiredi the main constraint being the short time base of typical flood hydrographs. It was planned to run the model with different return period floods to give an estimate of the location and depth of scour downstream of the spillway. There has been insufficient time to properly define a suitable discretization scheme and to test the model on the river without the dam. However initial model runs suggest that the majority of scour will be very localised; within 100m of the spillway for a 1 in 10 year flood.
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