Saturday morning saw about 10 Ruscombe Brook Action Group members meet at Acres End to get into the brook to remove silt.
Photos: the culvert under the unmade lane to Acres Place - flowing almost to capacity even when no storm or heavy rain - other photos of digging work - incl the back-breaking pulling of the barrow up the hill!
We got stuck in at this site with permission from the landowner - it had already been cleared in the past but last years heavy rains and this years have meant a huge build up - in places at least 18 inches deep from last time it was cleared.
We are under no illusions this is a short term measure to reduce the likelihood of the lane flooding - we need longer term measures - and indeed RBAG members will meet this Thursday with the newly appointed District Officer to consider if some actions might be possible. In my conversations with the guy it is clear he is keen to help - certainly we need a proper grill - the culvert also needs to be bigger but that is a big expense - plus we are after attenuation ponds to slow the flow of the brook up to this point.
Anyhow we did remove a lot of silt and start to try to create a sort of attenuation area but really a digger is needed. We are also awaiting advice on the best locations to take action - the recent Water21 studies (see earlier blogs) take an excellent Stroud-wide approach which includes Ruscombe brook, but so far we are still waiting for a practical plan of solutions for flooding at Puckshole and for pollution (See details of last our meeting here). As this has not materialised we are looking at more of a DIY approach - with help from one of the Water21 interns. He has given advice on how we can collect the data we need eg how quickly the brook rises and falls during rainfall events.
There is also a need to identify the flow of water downstream, and calculate the volume of water that is required to be stored upstream to prevent flooding downstream. Old attenuation sites need to be identified - including sites right to the top of the valley. Anyhow there will be more on this as the project progresses.
In terms of our morning of digging we were able to remove many barrow loads of silt and hopefully reduce the risk of flooding a little. Attempts were also made to remove stuff from the culvert - a huge boulder was removed but we suspect more is in there blocking the flow.
In terms of digging this site we were all aware we needed to take some care as this site was identified as the most polluted along the stream. This was shown in the MSc student, Ismaela's and also in this summers Ecological Survey of biodiversity in Ruscombe Brook by two RBAG members.
Alastair and Erfan conducted an informal biodiversity study of the whole brook using kick sampling and also searching under stones. They surveyed 11 test sites and used the following test to indicate water quality, using these indicator species:
1. Poor quality – tube worms
2. Low quality – bloodworms, mosquito larvae
3. Not too bad – freshwater shrimps
4. Good quality – mayfly larvae
5. Excellent quality – stonefly larvae
To me this is all fascinating - and good news - having been able to reduce the number of sewage incidents RBAG members can be rightly pleased that the biodiversity is improving - anyway see here is what they wrote about their survey:
We found tubeworms at the lake at the Lawns but not at Puck's hole. This means that the lake condition is relatively long term and stable i.e. it took the worms a long time to get there and set up home. But importantly we did not find worms at pucks hole, only shrimps. This indicates that the siltation there was a short term, sudden event due to increased local erosion. The shrimp swim about actively and colonise everywhere quickly, but worms take years to colonise a bit of mud. All this means that (theoretically) puck's hole can be easily returned to its former glory by us stopping excess erosion. However we cant do much for the lake except wait for it to naturally mature (reeds would help this process).
Other findings included from their work: The top areas were shallow and fast flowing, and diversity at the Charleys lake was excellent, showing lots of life. Mayfly were found here. The top of Julia’s field was healthy, with stony bottom and fast flow. Other life that was noted - dippers and woodpeckers, water scorpion, dragonfly nymphs and caddisfly larvae. There is a healthy breeding population of sticklebacks at Hamwell Leaze. There is evidence of re-stabilisation of previously eroded high banks through natural plants re-establishing in these areas around the cattle drinking area. Poor diversity was associated with high siltation and bottlenecks in the flow of the water, such as Pucks Hole and Lake at the Lawns, where there were many tube worms. At both of these sites the flow is restricted above the pucks hole culvert there is black anoxic foul smelling silt and foam. There is evidence of an oil film at Pucks Hole and also here Ismaila’s report identified a coliform spike. It was noted that a recent sewage incident may significantly impact upon the present level of biodiversity.
Overall conclusion is that average diversity in the brook as a whole is reasonably good, but there are notable troublespots where quality is poor. RBAG aims to have the same level of water quality and biodiversity at the top of the brook as at the bottom and in between. Man-made bottlenecks and erosion cause siltation and have a negative impact which needs active management.