Foot Meadow hydraulic modelling
Foot Meadow Island is located in the centre of the City of Northampton, England. It is a 620 m long island formed in the 12th century when a leat (channel) was cut from the River Nene to feed a mill. The leat forms the northeast channel around the island. The more meandering southern channel from the A4500 south is part of the original course of the river. The site of the mill lies under where Towcester Road Bridge cuts across the southern tip of Foot Meadow Island.
The river and leat have been classified under the Water Framework Directive as heavily modified and moderate status. Issues associated with water quality, weed invasion and provision of habitat for fish and invertebrates have been identified.
The River Nene Regional Park have proposed a range of remediation measures aimed at improving the instream habitat, mitigating flooding and reducing danger to the public. Key aspects of the proposal include removal of some sheet piling, regrading of parts of the river bank around Foot Meadow Island and the installation of coir rolls. Read more about the project here.
The proposed works aim to make Foot Meadow Island a safer and more environmentally friendly place. The project aims to help increase in-channel morphological diversity as well as improving floodwater capacity and reducing the risk to the public of injury or drowning. The completed works could be used as a demonstration site for other potential river habitat improvement projects, as well as an educational resource for schools and universities.
Syrinx Environmental for the River Nene Regional Park
What we did
The objective of the work was to quantify, using two-dimensional hydraulic modelling, any potential impacts of the proposed works at Foot Meadow Island on local water levels and flows.
We undertook the modelling using a two dimensional model (DHI Mike 21) using inputs from the existing modelling of the area.
A series of models for the area have been developed using the Flood Modeller Suite, incorporating TUFLOW. Data from this model was used to provide inputs for the Mike modelling.
A range of design events were simulated, varying from 1 in 2 Annual Exceedance Probability (AEP) up to 1 in 1000 AEP. Climate change scenarios were also modelled.
- Extracting flow data, structures and bathymetry for the existing situation from the existing model;
- Setup of a hydraulic model of the island, river, leat and floodplain with boundaries at the incoming and outgoing river points for the existing situation and model water levels and flow;
- Taking the earthworks design for the proposed upgrades, developing an updated model and simulating water levels and flows for the same events;
- Deriving change in water levels and flows with the proposed change; and
- Documenting the methodology and results in a comprehensive report.
The outcome of the modelling was used to demonstrate if the proposed works had any negative impacts on local flood levels or flow states. This information was presented to the regulator in support of the project. A report was prepared which presented the assumptions used in the modelling and predicted outputs.