Development and implementation of AWRA-R flood inundation module

[摘要] This report describes the development and application of the floodplain inundation modelling component of AWRA-R modelling system. Two storage-based conceptual approaches have been developed for building the flood inundation modelling capability in AWRA-R modelling system. Approach 1 is a simple method suitable for data limited environment. In this approach during any flood event, flow in a river reach within a floodplain is partitioned into two components, in-stream and overbank flow, based on the in-stream capacity. A flood volume-area relationship derived from the flood inundation time series is used to estimate flooded area for the overbank flow. The losses due to evaporation and groundwater seepage from floodplain are calculated using the estimated flooded area.LiDAR based DEM is used to divide a floodplain into multiple cell-based storages. Each DEM cell is considered as a floodplain storage. For a modelling reach, river is assumed to be a single storage with multiple outlets. The LiDAR DEM is corrected for average slope, bridges and culverts prior to establishing hydraulic connections between cells starting from the outlets of the river storage using a filling technique. Changes in floodwater volume in hydraulically connected floodplain storages are calculated for every centimetre increase or decrease of water level above the height of the outlet at the lowest level. This information is used to establish a relationship between overbank flow-flood inundation volume and area upto the maximum possible flood event in the reach. The relationship can be used in conjunction with the time series of overbank flow and floodplain volume obtained from Approach 1 to generate time series of inundation maps for any simulated flood event.Approach 1 was implemented in all floodplain reaches of Murray-Darling Basin. The parameters of Approach 1 were calibrated as part of the joint calibration of AWRA-R model by invoking the flood module in the floodplain reaches. The results in different floodplain reaches demonstrate that AWRA-R model with Approach 1 flood inundation module performed reasonably well in most of the floodplain reaches in both calibration and validation periods. The NSE values of the simulated results in floodplain reaches in most of the regions (Condamine-Balonne, Namoi, Macquarie-Castlereagh, Lachlan, Murrumbidgee, Goulburn-Broken and Loddon-Avoca) were similar to the overall regions. The agreements are better in floodplain reaches for Barwon-Darling and Murray regions. For the Border rivers and Gwydir regions, the agreement in floodplain reaches were less than the regional average. Bias was consistently low in the floodplain reaches in most of the regions except for Condamine-Balonne, Murray and Goulburn-Broken regions. Approach 1 model has produced the daily time series of floodplain stores and fluxes. The mass-balance analysis shows that the long term mass balance error was negligible for all floodplain reaches. Due to simplicity of the approach with limited amount the data requirement, Approach 1 is suitable for most of the floodplains. However, this approach is not capable of producing spatial dynamics of flood inundation. Approach 2 was implemented in two selected reaches of Murrumbidgee floodplain, where LiDAR DEM was available. A comparison of the results with the simulated outputs of MIKE21 two-dimensional hydrodynamic model and the flood extent maps derived from Landsat TM data for two recent flood events has shown that the performance of Approach 2 is highly satisfactory both in terms of flood extent, depth and duration. This approach is capable of producing the spatial and temporal dynamics of flood inundation characteristics at a very high resolution. A key advantage of Approach 2 is the quick run time compared to a two dimensional hydrodynamic model. The limitations of this approach is the requirement of very high resolution topographic data and the inability to produce flood velocity.

[发布日期] 2013-06-18 [发布机构] CSIRO

[学科分类] 地球科学(综合)