Layer: Discharge 1810 Cumecs (ID: 27)

Name: Discharge 1810 Cumecs

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Description: Flood map boundary generated through ArcGIS's floodplain modeling using data generated by Steve Ratcliffe with BMT WBM and Hydro Consulting. February 2011.Tamar River Flood Water Surface Profiles for Multiple Discharge Emergency Management Flood Level MapGeneralThis map indicates water surface profiles from Hobblers Bridge Rd in the North Esk to down stream of Hunter Cut in the Tamar. The purpose of this map is to define an array of water surface profiles for emergency management purposes. Flood frequenciesNote: The AEP of 1:100 for example is the probability on the average that a given flood height will be equalled or exceeded in any year. A 1:100 AEP flood height has a 1% chance of being exceeded in any one year. ARI or Average Recurrence Interval is the average period between events of a nominated size.Annual Exceedance ProbabilityProbability of the design flow being equalled or exceeded at least once in a 20 Year Period50 Year Period1:2064%92%1:5033%64%1:10018%39%1:20010%22%The frequencies of flooding in the Tamar River system have been derived from data collected during the past 100 years in the South Esk. The extent of flooding shown on this map is approximate only.DischargesHydro Consulting where commission to review the South hydrology at Trevallyn. They recommended that the following flood estimates should be adopted. Flood Return Period in yearsSouth Esk Flood discharge values recommended by Hydro Consulting 2008 cumecs2018105023301002910200Monte Carlo Range1850 3430 39905004630The recommended median 1:200 year AEP flood discharge is therefore 3430 cumecs a reduction of 1270 cumecs (27%) on the estimate used in 1994. For any given AEP there are a range of flood discharges which are possible. A range of flood peak values was derived using a Monte Carlo analysis in which the following parameters were varied: The range in values due to the stochastic variability of initial losses and temporal patterns with constant continuing loss, gave 5thand 95thpercentile values of 1850 cumecs to 3990cumecs for the 200 year flood Where continuing loss was varied the 5thand 95thpercentile values were 1720 cumecs and 4130 cumecs.Flood SurfacesThe flood surfaces shown on the plan relate to the larger floods which will emanate from the South Esk. The levels in the North Esk are therefore largely due to backwater effects.The flood surfaces were modelled in TUFLOW by BTM WBM using a scoured bathymetry established with the Hydrodynamic model RMA10s.The production of the maps and associated hydraulic and hydrological studies were project managed by Steve Ratcliffe.This map is based on the following reports:River Tamar & North Esk River Flood Study, Final Report November 2008 by BMT WBMHydrodynamic Modelling of the Tamar Estuary December 2008 by BMT WBMTrevallyn Flood Frequency Review August 2008 by Hydro Consulting

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