Chudleigh Drainage and the Kate Brook
10th January 2017
Doug Hellier-Laing, Mike Moyse and Mike Underwood met with TDC Drainage Manager Mark Fox to establish some principles for resolving current and potential flooding problems in the Kate Brook.
It was decided that the areas for discussion came under five topic headings. The meeting convened in the town hall where current CTC research was discussed, including rainfall data etc., but soon included visits to various sites along the leat and Kate Brook itself.
The outcome of the meeting was very positive although the implementation of the solutions could be both time and partially financially bounded.
Water volume in
We agreed that the volume of water entering the leat could well be influenced by the amount of water coming off the A38 Expressway particularly during either heavy downpours or sustained periods of rain. The flooding of the Kate Brook Sports Centre was largely due to more water flowing into the leat than could quickly get out, primarily through blocked gratings at the sports field itself and at Kate Brook Bridge adjacent to Cricket Field Road. (Upon examination Mark indicated that both sets of grating were not to standard and indeed probably added to the flooding problem. He volunteered to research the design and come up with a more suitable arrangement including platforms upon which an operative could stand to periodically remove the build-up of debris). In addition, to avoid flooding themselves, owners of properties alongside the leat (e.g. The Chapel), had breached the bank, thus allowing water to overspill the carpark and down onto the playing field itself.
Mark has access to all the historic drainage drawings and can ascertain the exact route of the feed in from the A38, bearing in mind that there will be other springs and water courses adding to the volume. Mark is in contact with Martin Hutchings (DCC Flood and Coastal Risk Manager) and through him with David Godwin-Hughes (Highways England) who now handle all drainage for DCC. Solutions under consideration could be the attenuation of the water before it hits the leat, either by tree planting or attenuation ponds or such like, or the piping of the A38 water straight into Kate Brook. The final solution will be the result of some detailed analysis, work which Mark will be able to facilitate. It is thought that Highways England might have some budget for a project of this type.
There was no doubt that reducing the water flow, or at least the sudden rush of volume, would be key to reducing flood risk. One interesting comment was that if a flood risk was still prevalent in the future all building in or near the sports field might be on “stilts”!
It was explained that the gratings were now checked regularly and daily in times of heavy weather.
Mark will speak with DCC and Highways England to seek ways that these might be modified to ensure they work more efficiently and are safe for operatives to clear them with a hand tool (rake!).
Bank erosion and Potential Narrowing of the Kate Brook by “riparian owners”
It became clear that bank erosion was caused by three elements. Firstly by water volume under pressure entering the Kate Brook from the spillway adjacent to the sports field after leaving the leat; this created eddy currents which were washing the bank away; secondly by something similar happening on the opposite bank where water gushes off Clifford Estates land, and in the same proximity to the spillway. Both these inputs of water set up a huge maelstrom of powerful water which is eroding the bank on either side; and thirdly (it would appear) by owners of various properties who have installed gabion baskets along their banks. Mark was content that in principle these were acceptable provided that a) permission had been granted for their installation and b) the installation did not encroach in any way the width of the river at that point. Gabions, or indeed any other obstruction, will materially affect the water flow, thus creating more eddying and silting.
TDC will write to all owners (Riparian Owners) of property adjacent to the Kate Brook advising the dates that he (Mark Fox) will be walking the river photographing and mapping the pinch points in order that a full recommendation for action can be made.
Details of gabions, unsuitable river bank constructions, bank encroachment, tree roots or vegetation growth will be made, particularly if river narrowing occurs and retrospective action will be suggested at the cost of the riparian owner. The letter will point out that permission is required for any construction work, however meaningful.
Water volume out
It was agreed that flooding could also be caused by water not being able to escape its course quick enough, so a “bore” effect was created. It is possible (although unlikely) that the river bed level has risen over the years due to silt build up or, again, the river being narrowed or blocked.
Mark confirmed that he has a statutory right to walk the river from source to sea (!) and will investigate the course of the river, particularly beyond Palace Mill and Palace Farm.