Grade A5
Project Title: “An evaluation of flood modelling techniques on a stretch of the River Devon, Clackmannanshire”
Abstract
Earths weather patterns are changing at a rapid rate due to anthropogenic induced climate change, which could see a variation and intensification of water cycles. With these changes there is an enormous challenge in adapting and mitigating against the severe threat of flooding which could be achieved via river flood modelling, and the subsequent correct implementation of natural flood management practices.
LiDAR terrain mapping is a key tool in the fight against flooding, however Scotland has fallen behind other regions in Great Britain achieving only 40% LiDAR coverage compared to partners in England and Wales with 100% coverage. Therefore this study seeks to ascertain, via an evaluation of flood modelling techniques, if that in the 60% of Scotland were LiDAR black spots occur, is UAV-SfM/Photogrammetry a viable alternative for flood modelling.
Via a range of models and flood simulations completed the study found the importance of using the correct cell size and N-values within HEC-RAS 2D modelling for the most accurate results. Through a comparison of 1D modelling and 2D modelling, if computing processing power and time allows, models should be run as 2D with the smallest cell size (catchment size dependant) to ensure the most accurate outputs.
Through a continuation of varied flood modelling simulations, the study also concludes that currently Photogrammetry derived DTMs aren’t a viable alternative to LiDAR derived DTMs due to the varied and also inconsistent differences in flood results, such as Photogrammetry models often having less flooded area and flood volume, but also having a far greater depth of flood for every HEC-RAS model conducted. The study also concludes that the ArcGIS Pro Flood Simulation isn’t a viable alternative to HEC-RAS, and while it may be useful for short rainfall flood events in small areas, it isn’t an engineering tool that is comparable to the accuracy of HEC-RAS produced results.
Aim & Objectives of the project
Aim
The primary aim of this project is to conduct an evaluation of varied flood modelling techniques along a section of the River Devon to determine the effectiveness of SfM-UAV derived DEMs and different flood modelling applications. This could be used to assist Forth Rivers Trust with future implementation of natural flood management systems within the Forth River catchment.
Objectives
The aim will be met by the following objectives:
- Replicate a flood model based on the method of the existing commercially produced report (2D HEC-RAS with SEPA LiDAR data) and compare results to that from the commercial report.
- Using same data as Objective 1, conduct a 1D flood model (HEC-RAS) and compare results to the 2D model from Objective 1.
- Using photogrammetry, convert Forth Rivers Trust drone image data to a DTM/DSM file, and conduct both 1D and 2D models (HEC-RAS) and compare outputs to the results of Objectives 1 & 2.
- Conduct an ArcGIS Pro flood simulation using both SEPA LiDAR and photogrammetry derived DEM and compare to 2D models results from Objectives 2 and 3.
- Create a comprehensive method to enable Forth Rivers Trust to apply the method on future study sites within the Forth Rivers catchment area.
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