Hydrology & Hydraulic Modelling
Darwin Tributaries
Keywords:Hydrological Analysis, Flood Mapping, TUFLOW Pluvial Flooding
TUFLOW Pluvial Modelling to determine catchment boundaries
Client, Architect & Other Organisations
EA North West Region (North Area)
Description
The Darwen Tributaries project involved the development of hydraulic models for fifteen previously unmodelled tributaries of the Darwen in Blackburn, for which the Environment Agency recently accepted responsibility from the local authority.
These tributaries, many of them from small, steep, heavily urbanised catchments with long culverted sections, have a history of flooding due to blockage and lack of channel capacity.
Scope of Work
Edenvale Young were approached to undertake the hydrological and hydraulic modelling of these tributaries. The project included:
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The development of an accurate ground model of the area based upon LiDAR data supplied by the Environment Agency.
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Analysis of the catchment areas for each tributary. Many of the catchments included features such as mill leats and were extensively urbanised. The areal extent of catchments contributing to the tributaries required map-based analyses using GIS software and two-dimensional rainfall modelling to accurately define catchment boundaries.
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A hydrological analysis of each of the tributaries at a number of locations as well as a hydrological analysis of the Darwen itself was carried out. This was undertaken using several methodologies including the Rainfall run-off, ReFH, Statistical, IH24 and Rational methods. Due to the very small size and the steepness of the catchments, models such as the FEH rainfall run-off method and the ReFH method were deemed unsuitable for the problem and statistical methods were used.
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The development of a wide area model including a number of ISIS, double-precision TUFLOW and linked ISIS-TUFLOW models. These will incorporate rainfall models applied both as point sources and as global, distributed inflows. This model will be calibrated at the Ewood velocity area gauge on the Darwen.
The models were run for a variety of events and blockage scenarios as well as for undefended scenarios for flood mapping purposes.