USC FloodStudyUpdate Report - Flipbook - Page 252
separate models covering Lowes Creek and Thompsons Creek (West Model), South Creek (Mid Model)
and Bonds Creek, Scalabrini Creek, Kemps Creek and Rileys Creek (East Model). If the model is to be
used to assess flood impacts of a precinct-scale development, then the subcatchment delineation may
need to be revised based on the proposed landform. Subcatchments to proposed structures (such as
culvert crossings and detention basins) may then need to be delineated.
Updated subcatchment boundaries (either for base case conditions or proposed conditions) should be
delineated using GIS or CAD software, and are to be mapped in the impact assessment report. The
number and size of subcatchments between the base case and proposed case for an impact assessment
should be reasonably consistent.
3.3. Model Parameters
The primary subcatchment parameters used in XP-RAFTS include:
Area,
Slope,
Impervious fraction,
Surface roughness.
These parameters should be updated for the new subcatchments that have been delineated. Each of these
Bx
been used throughout the model. These have been assigned based on the length of the flow path through
the catchment and an estimated stream velocity of 1 m/s. Since local catchment inflows are used in the
TUFLOW model, these lag links are not required in order to obtain flows for use in the TUFLOW model.
The XP-RAFTS model may be used for preliminary options assessment for design of flow detention
structures, but for the impact assessment report all hydraulic routing should be undertaken in the TUFLOW
model.
3.3.1. Area
The catchment area should be calculated in hectares using a GIS program.
3.3.2. Slope
The slope parameter was calculated using CatchmentSIM software. If this program is not used, the
catchment slope should be calculated by considering the average catchment slope for flow paths within the
catchm
3.3.3. Impervious Fraction
Australian Rainfall and Runoff 2019 (ARR 2019, Reference 1). ARR 2019 identifies three types of areas for
the purpose of estimating urban storm losses:
Directly Connected Impervious Areas (DCIA) which are impervious areas directly connected
to the drainage system;
Pervious Areas consisting of parks and bushland areas; and
Indirectly Connected Impervious Areas (ICIA) which consist of impervious areas which are not
directly connected to the drainage system and the pervious areas which interact with indirectly
connected impervious areas.
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118112: 201030_USC_Regional_Model_User_Guide_Final: 30 October 2020
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