1 21/10/2013 MT JL 2 08/05/2014 MT JL DISTRIBUTION DESTINATION REVISION 0 1 2 3 CoGG CoGG (pdf) CoGG (doc) BMT WBM File BMT WBM Library 1 1 0 1 0 6 1 0 1 1 1 1 1 1 1
modelling of these 1D elements (culverts/pipe networks), ensures that the capacity and conveyance of these systems are accurately modelled. Each square grid element contains information on ground topography, sampled from the DEM at 1 m spacing in the 2 m domain and 2.5 m in the 5 m domain, surface resistance to flow (Manning’s ‘n’ value) and initial water level. Seventeen areas of different land-use type, determined from planning maps, aerial photography and site inspections, were identified for setting Manning’s ‘n’ values. These are summarised in . Figure 48 TUFLOW Model Setup Table 412 2D Domain Manning’s ‘n’ Coefficients Land use Manning’s n Low Density Residential 0.15 Residential 0.2 High Density Residential 0.4 Commercial/High Density Industrial 0.4 Building Envelope 1 Open Space – Maintained Grass 0.035 Open Space – Unmaintained Grass 0.05 Open Space – Low Density Vegetation 0.55 Open Space – Medium Density Vegetation 0.65 Open Space – High Density Vegetation 0.1 Sports Ovals 0.03 Easements 0.045 Developed Parks/School Fields 0.05 Schools and Public Areas of Similar Type 0.2 Cemetery 0.1 Roads 0.025 Open Water 0.03
relationships. Total damages for each flood event were determined by summing the predicted damages for each individual dwelling. The AAD was then calculated. The AAD is the average damage in dollars per year that would occur in a designated area from flooding over a long period of time. In many years there may be no flood damage, in some years there will be minor damage (caused by small, relatively frequent floods) and, in a few years, there will be major flood damage (caused by large, rare flood events). Estimation of the AAD provides a basis for comparing the effectiveness of different management measures (i.e. the reduction in the AAD). The AAD is the area under the probability-damage graph. Ideally the probable maximum flood damages are included in the AAD analysis, and it is also necessary to assume a flood AEP in which no damages occur. As no flood larger than the 1% AEP event was modelled, the graph was extrapolated, and it was assumed that no damages would occur in the 50% AEP event. Existing Conditions Flood Damages The total existing conditions damages for each design flood event are presented in Table 61. They are also illustrated in Figure 61. The existing conditions AAD for the Highton study area, as presented in Table 61, is $389,000. Table 61 Existing Conditions Damages Summary Event Existing Case (Years ARI) AEP Residential Damages Commercial / Industrial Damages Total Indirect Damages Total Damages Incremental Average Annual Damages PMF* 0.0% $3,430,000* 100 1% $2,284,000 $77,000 $708,000 $3,069,000 $32,000 20 5% $1,206,000 $45,000 $375,000 $1,626,000 $94,000 10 10% $816,000 $28,000 $253,000 $1,097,000 $68,000 5 20% $519,000 $17,000 $161,000 $697,000 $90,000 2 50% $105,000 Average Annual Damage $389,000 *PMF damages are an extrapolation of the 1% AEP data, i.e. they were not calculated using PMF flood levels. Figure 61 Existing Conditions Damages Probability Curve
Table 71 Mitigation Option Element Screening Element Type Strategy Elements Comment Assessed Urban Structural Measures Pipe system upgrade Considered Pumps Not appropriate Soakage Pits Not appropriate Retarding Basin Considered Diversions Considered Floodways Not appropriate Open Drain Not appropriate Channel Improvement Considered on small scale to compliment retarding basin works Bund Walls Not feasible Lot scale infiltration Not appropriate Lot scale detention Not appropriate Individual Property Floodproofing Possible, however very expensive Measures Planning Scheme Amendments Considered Voluntary House Purchase Considered Voluntary House Raising Considered Rural Structural Measures Levees Not applicable Floodwalls Not applicable Floodways Not applicable Floodplain Modification Not applicable Channel Improvement Not applicable Individual Property Floodproofing Not applicable Flood Storage Not applicable Diversions Not applicable Non-Structural Measures Flood Warning Systems Not applicable Land Use Planning Not applicable Floodplain Education Programs Not applicable Purchase and Relocation Not applicable Information and Data Collection Not applicable Planning Scheme Amendments Not applicable Regulation and Enforcement Not applicable Detailed Assessment Non-Structural Options The non-structural options considered for the economic assessment were voluntary house raising, voluntary house purchase and amendments to the planning scheme. Voluntary house raising was not considered further because it has limited application in this catchment, where many of the flood affected buildings cannot be economically raised. This is due in part to many vulnerable houses being of slab-on-ground construction. Voluntary house purchase was not considered viable because of the cost of the buy back and re-construction.
Public acceptability. There would be issues related to this scheme as works are proposed to be undertaken on existing road infrastructure disturbing transportation. There would be issues related to this scheme as works are proposed to be undertaken on existing road infrastructure disturbing transportation. There may be issues related to loss of access to Highton Recreation Reserve during construction and the layout post construction. Same as Scheme Two. Issues relating to Council being seen to be doing nothing structurally about the problem. .