Geomorphological Modelling at Pont Briwet using TUFLOW FV

These were two EVY presentations related to geomorphology in the TUFLOW 2015 conference. This post describes the work Edenvale Young undertook on the Dwyryd Estuary in North Wales.

In 2012 Edenvale Young were asked by Hewson Consulting Engineers (consulting bridge engineering specialists) to assist with the design for the replacement of the 1867 road and rail bridge at Pont Briwet. Edenvale Young undertook a wide range of services including: the design of scour protection beneath the bridge and rock revetment protection to the approach embankments. In addition, to the civil design works, we also developed strategies for assessing and monitoring geomorphological change and water quality during construction and undertook a flood risk assessment for the project.

Pont Briwet before construction

The Dwyryd estuary is classified as a Special Area of Conservation due to the highly dynamic nature of the geomorphology within the estuary.The geormorphological assessment is included historical evaluation of change within the estuary, hydraulic modelling to assess the potential impact of the works during construction, pre-construction LiDAR and LiDAR / survey monitoring during construction.

The geomorphological aspects of the project were particularly challenging in the temporary works condition which included the installation of a temporary causeway and cofferdams within the channel (see a timelapse video). These works temporally reduced the channel width from 120m to a minimum of 42m to facilitate the installation of the bridge columns. The most significant impacts of the reduction in width was the development of an 11m deep scour hole on the downstream side of the bridge and recession to salt marshes on the north bank of the estuary.

John Yong presented the georphomological modelling work undertaken by Edenvale Young.The modelling was based on the use of TUFLOW FV with the MORPH module. The model was calibrated using an event in September 2013 soon after completion of the temporary causeway. This resuted in the initial development of the scour hole on the downstream side of the bridge. Over a period of 2 weeks the scour hole grew to 4.5m in depth. John discussed the measures and parameters used to calibrate the model and whether a successful calibration was achieved.

The replacement bridge was finally open to road and rail traffic earlier this year. If you would like to find out more about this project please please contact John Young ( or Gerald Morgan ( You can also visit the Edenvale Young's Flickr site.

Project Details Client: Gwynedd County Council, Network Rail Main Contractor: Hochtief UK Designers: Hewson Consulting (Bridge Design), Edenvale Young Associates, Beazley Sharpe Railways, Stillwell Partnership