Two weeks ago RRC held two training courses back-to-back focusing on Natural Flood Management (NFM).
Day 1 - Mapping Historical Floodplains using the Hydrogeomorphological Survey
The first of our Natural Flood Management courses was titled “Mapping Historical Floodplains using the Hydrogeomorphological Survey”. The aim of this course was to introduce a method for producing a map which represents inundation zones and flood pathways on a floodplain.
The first step was to get to grips with Laurent Matheiu’s HGM method that he has been working on for over 20 years. The method uses freely available maps and data as well as site surveys to identify inundation zones on the floodplain. Laurent talked through the identification of these zones and provided examples of where the method has been applied.
Then it was time for the attendees to have a go themselves. Armed with colouring pencils, an OS map and LiDAR data, they were asked to identify the various inundation zones on the floodplain as well as some key morphological features. This was a lot harder than we thought and it soon became clear that this method, whilst simple to implement, requires practice and experience.
To help with this, we then went out on site to the exact location that attendees had been attempting to map. Laurent walked us from one side of the floodplain to the other, pointing out visual markers such as terraces, flood extents and flow pathways. After this we walked into the village to see how visual markers are still visible in urban areas, with increases in slope defining inundation boundaries. Finally, Laurent took us down to the pub where there are historical flood markers. He pointed out that these are level with the visual markers which he had identified on the floodplain.
The final part of the day was back in the training room. Here Laurent’s original map of the site was revealed to the attendees. We were given time to study the map and compare it to our own. Laurent had drawn his boundaries using GIS and it looked very impressive. He then talked through another case study where he had compared his boundaries to historical and modelled data in Chippenham. His map was incredibly accurate and showed the value and reliability of this method.
It was an interesting day which not only introduced a very useful method for floodplain mapping but also encouraged attendees to look at floodplains and their features in a way that maybe they hadn’t before.
Day 2 - Mapping Surface Runoff and Flood Storage Opportunities for NFM
The second course focused on identifying potential flood water storage zones and zones of water transfer. Marc and Laurent opened up the course with an introduction to the hydrological cycle, looking at how flood waters travel and accumulate creating ponds. Transfer zones include gully flow, field flow, muddy flow and flow through urban areas; and zones of accumulation include lowlands or depressions in the landscape which can encourage reduced flow and potential ponding. Runoff attenuation features and structures to retain flow were explored, including gully blocking and leaky dams to temporarily hold back water.
A Morpho-topographic method was developed using a naturalistic approach based on LiDAR and aerial photography, to identify artificial low points in the landscape. The group followed a guided, interactive session using MapWindow and QGIS software, carrying out analysis on a DEM of Thrift Farm, Buckinghamshire. We then worked to digitise the potential zones of transfer and zones of accumulation to create a map of storage opportunities. Participants engaged well in this session and shared ideas on flood issues in the landscape.
Following this session and a quick chat over lunch, the group travelled to Thrift Farm in Buckinghamshire to visit the site we had been looking at earlier. Laurent and Marc pointed out the depressions in the land and the slope of the area, and the group saw the potential runoff accumulations in the field. It was great to see the actual area we had been digitising – this helped me gain an understanding of the importance of modelling, and helped me think about the potential considerations for flood storage.
If you would like to try the software for yourself, they are free to download here:
Also LiDAR data is available here through the Environment Agency website.
Check out more photographs from this training course on our Flickr page!