Delivering Accurate Flood Mapping with ReFH2 and Hydrology+
- 3 days ago
- 3 min read
What our clients say:
“ Flood Modeller's Hydrology+ streamlined the hydrological study for the flood map challenge. We were able to integrate the hydrology within the Flood Modeller project itself, allowing quicker workflows. We will look to further improve the process with the Flood Modeller API.”
Gideon Miller, Flood Risk Consultant, Ridge and Partners LLP
Key Facts
A full hydrology assessment was required as part of a flood map challenge.
ReFH2 was selected due to the urbanised nature of the lower catchment, highly permeable upper catchment, limited flow data for statistical QMED estimation, and the need to account for mismatches between topographic and sewer catchment boundaries.
Sewer networks significantly altered natural flows, leading to complex hydrological catchments and the transfer of flows between these catchments.
A method was developed to calculate flows into and from the sewer catchment using RefH2's sewer export functionality.
Hydrology+ within Flood Modeller streamlined the workflow by allowing multiple hydrographs to be managed in a single environment and applied easily within the model. However, lots of manual data manipulation was still required. Future enhancements to the method will focus on automating these processes using the Flood Modeller API.
Why an Updated Hydrological Approach Was Required
Ridge was commissioned to undertake a flood map challenge. The watercourse had previously been modelled but had since undergone extensive river restoration works, including the removal of concrete channels and the reintroduction of meanders. The old model was no longer representative, and an updated model was needed to update flood maps. RefH2 was used to calculate inflows to the model due to:
The urban nature of the lower catchment made it suitable for ReFH2’s urban model.
The highly permeable nature of the upper catchment and the lack of available flow data to provide confidence in the estimation of QMED using statistical methods.
The major differences between the boundaries of topographic catchments and sewer catchments.
The ability to derive sewer catchment boundaries.
Modelling Flow Transfers with ReFH2 Sewer Export
Two topographic catchments were identified, with the sewer catchment having a major impact on the routing of flows within the catchments.
Within the urban area, three sewer networks were identified. Two of these aligned well with topographic boundaries, but the red sewer catchment did not. It discharged into the green catchment, despite most of the catchment being topographically part of the blue catchment.
This resulted in three catchments for the hydrology analysis to obtain flows for the model:
Blue and green: generally aligning with the initial topographic catchments, but with minor areas utilising the sewer export functionality in ReFH2.
Red: whole catchment drained by sewer.
To transfer flows between catchments, the ReFH2 sewer export functionality was used to import flows from neighbouring catchments into the red catchment. The following method was used:
ReFH2 analysis carried out on blue and green catchments using ReFH2, without utilising the sewer export functionality.
ReFH2 analysis conducted for the blue and green catchments, including sewer export areas.
The difference between the flow with and without sewer export is calculated for each catchment.
Difference summed to get total flows in sewer only (red) catchment.
This approach allowed us to simulate inter-catchment flow transfers, even though ReFH2 doesn’t support it natively.
Streamlining Hydrological Data Management with Hydrology+
Hydrology+ within Flood Modeller provided an integrated environment to manage all hydrological inputs, significantly improving workflow efficiency. The method used required multiple hydrographs for each inflow, as analyses included scenarios with and without sewer consideration. Using Hydrology+ reduced the need to manually organise files, minimised the risk of versioning errors, and streamlined the process of assigning adjusted hydrographs to the hydraulic model.
However, manual data manipulation was still required, and we will therefore look to use the Flood Modeller API to automate workflows. This will be used to improve the method by automating calculations required to obtain final flows. This will reduce manual processing time, improve reproducibility, and enable more efficient delivery of similar future studies.
Gideon Miller
Gideon is a Flood Risk Consultant at Ridge with two years’ experience using Flood Modeller. In his current role, he works across a wide range of projects, including hydrology assessments, surface water and fluvial flood modelling, flood alleviation schemes, climate change assessments, and property flood resilience.
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