Alice Springs Flood Investigation and Floodplian Mapping Study
WRM Water & Environment Pty Ltd; Northern Territory. Department of Lands, Planning & the Environment
E-Publications; PublicationNT; E-Books; EXTA1463
Made available via the Publications (Legal Deposit) Act 2004 (NT).; WRM Water & Environment (WRM) was commissioned by the Department of Lands & Planning (DLP) to undertake a flood study of the Todd River in the Alice Springs area. The aim of the study is to develop a 2 dimensional flood model, which allows flood flow in a complex flood plain to be modelled, to determine the extent and severity of riverine flooding in the town of Alice Springs and the Alice Springs rural area south of Heavitree Gap. The purpose of the study is to produce floodplain maps of the Alice Springs and its rural area for land use planning and counter – disaster purposes. This study is an extension of the Alice Springs Farms Area Floodplain Mapping Study (WRM, 2006), undertaken by WRM on behalf of the Department of Planning & Infrastructure in 2006 in order to develop detailed Todd River floodplain maps for the rural area south of Alice Springs.
1. INTRODUCTION -- 2. CATCHMENT DESCRIPTION -- 3. AVAILABLE DATA -- 4. CALIBRATION AND AND VERIFICATION EVENTS -- 5. HYDROLOGIC MODEL CALIBRATION AND VERIFICATION -- 6. HYDRAULIC MODEL DEVELOPMENTLOPMENT -- 7. HYDRAULIC MODEL CALIBRATION -- 8. FLOOD FREQUENCY ANALYSIS -- 9. DESIGN EVENT HYDROLOY -- 10. DESIGN FLOOD LEVELS AND EXTENTS -- 11. CONCLUSION -- 12. REFERENCES
Flood control -- Northern Territory -- Alice Springs; Flood damage prevention -- Northern Territory -- Alice Springs; Floodplain management -- Northern Territory -- Alice Springs; Alice Springs Flood Investigation; Floodplain Mapping
WRM Water & Environment Pty Ltd
vii, 95 pages : colour maps ; 30 cm.
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0269-02-C1 12 October 2015 85 11 CONCLUSIONS The town of Alice Springs is situated on the banks of the Todd River, north of Heavitree Gap. The north-western extents of Alice Springs are located adjacent to the western bank of the Charles River, a major tributary of the Todd River. The Charles River joins the Todd River at Anzac Hill, immediately to the north of the Alice Springs CBD, and approximately 4.2km north of Heavitree Gap. The Alice Springs rural area is located on the floodplain of the Todd River to the south of Heavitree Gap, and extends approximately 9km south-east to the Amoonguna settlement. Both the township of Alice Springs and the rural area are potentially impacted by flooding from the Todd River (including the Charles River). The various local drainage systems, including the town stormwater drains and Chinamans Creek north of Heavitree Gap, and Ilparpa Swamp, St Marys and Emily creeks south of Heavitree Gap also have an impact on flooding. This investigation has focused on riverine flooding from the Todd and Charles rivers, and should not be used to determine design flood levels or extents for any of the local drainage systems described above. An URBS hydrologic model was developed to estimate flood discharge hydrographs for a range of design floods from the 20 Year ARI to the PMF draining to the study area. The URBS model has been successfully calibrated against the March 1983, March / April 1988 and April 2000 flood events, and successfully verified against 11 other historical flood events of varying magnitude. A set of global catchment parameters for the URBS model was developed and were left unchanged for all calibration and verification events (refer Section 5). The initial loss and continuing loss rate were adjusted (within reason) for each calibration and verification event in order to achieve the best fit between recorded and predicted peak discharges. Due to the uncertainty with regards to the accuracy of the Heavitree Gap stream gauge, the URBS model calibration initially focussed on achieving the best match at the Wigley Gorge stream gauge, followed by achieving an acceptable match at the Anzac Oval stream gauge. The URBS model calibration and verification results are considered acceptable, and it appears the hydrologic model is adequately reproducing historical flood discharges based on the available input rainfall data. The calibrated URBS model was used to estimate design flood discharges throughout the Todd River catchment for 20, 50, 100, 200 and 500 year ARI storm events and for the PMP event. The design discharges estimated using the URBS model are consistent with results from the flood frequency analyses undertaken for Wigley Gorge and Anzac Oval stream gauging stations. A TUFLOW (fully two dimensional) hydraulic model was developed to estimate design flood levels and the extent of flooding for the above range of design floods. The TUFLOW model has been successfully calibrated against recorded stream gauge data and surveyed debris marks from the two largest Todd River flood events for which data is available, the March 1983 and March / April 1988 floods. A successful calibration was also achieved for the April 2000 flood event. The model was verified against recorded stream gauge data for the three flood events which occurred in January, February and April 2010. The results of the TUFLOW model calibration and verification are considered acceptable. In a similar manner to the WRM (2006) study, the TUFLOW model is generally unable to reproduce