Rivers have formed the backbone of civilisations and carved the lifestyles of the peoples who have lived near them. What about Newnham's Bin Brook ? What influence has it had ? Could it join the present vogue of books about rivers and their influence ? Hardly maybe, but it has had and continues to have a significance influence on the landscape, both natural and man made, and architecture of Newnham
Bin Brook is the main contributor to the myriad of streams and channels in the Backs behind St Johns and Trinity colleges. Between Queens and Grange roads it forms a major feature of Fellows gardens and College gardens. At Robinson it is the catalyst for the college's delightful gardens; at the Needham Oriental Studies Institute it is a particular feature of the building design and gardens and at Clare Hall West who knows. So maybe in its quiet way it has had and will continue to have an influence. Maybe one day there will be a treatise (or even a book) on the natural history and influence of Bin Brook on the life of Cambridge.
So what about Bin Brook ? How many people have heard of it or even seen it? Well this obscure stream, including its southern tributary (ditch), certainly had an impact on Sunday 21 October. Over 20 houses on the Gough Way Estate were flooded plus several houses in Barton Road and in the Fulbrook road area. Houses were also flooded at the Clare Hall West site and Robinson College also came every close to be having its lower floor, including cafeteria, inundated. Indications are that the damage to property in the Gough Way area could be a very large amount, plus of course the emotional affects of having one's house "invaded".
So maybe a short description of the storm on the 21st and of Bin Brook is justified, along with some ideas about what could be done to avoid it happening again. This includes the southern tributary, which passes behind the Cambridge Rugby Club in Granchester Road and enters the lake behind Fulbrook road. This "ditch", called "Full Brook" certainly lived up to its name on the 21st, being found to be quite inadequate.
Firstly the storm. This was one of the most intense ever to hit Cambridge and its environs. The rainfall was 90-98 mm in 18 hours, which is more typical of a heavy monsoon storm in the Indian Sub-Continent. The Environment (EA) website indicated a 1 in 140 year return period for the storm, which translates crudely into a 1 in 75 to 100 year return period flood event. Latter correspondence with the EA indicated that the return period of the storm may have in fact been over 250 years.The rainfall isoyhet (contour) map for the whole country on that day showed the summit over Cambridgeshire.
Now back to Bin Brook. Its catchment up to where it joins the Cam is 18 km2 and it rises at a high elevation (by Cambridgeshire standards) of 60-65 m above Ordnance Datum in Hardwick (Gough Way elevation is 10 m). The catchment is mostly agricultural land, but also Coton, part of Hardwick and also a considerable length of the M11 (more about this later). Unusually for rivers and streams in the region, it has no water meadows or significant flood plains and as a result there is considerably more direct runoff. This is reflected in the present estimates for the 1 in 100 year flood event (criteria for urban developments) of 6-7 m3/s for Bin Brook, whereas the estimate for the Cam at Jesus Green Lock with a catchment area some 50 times larger is 55 m3/s, only 8 times higher.
Well what can be done both with respect to Bin Brook and Full Brook? Clearly this lies in the court of the Environment Agency to examine. Blame for the flooding has been attached, possibly wrongly, to several downstream causes, such as the operation of Jesus Green Lock and a barge sunk near Magdalen Bridge. However the fact is that this was a very intense storm and the view is that the solution needs to be found upstream of the city boundary. One contributing influence, and probably particularly for the southern tributary, is the M11. This appears to have no balancing ponds whereas in recent years there has been a Government requirement that all new developments have SUDS (Sustainable Urban Drainage Systems), basically on site solutions to ensure that the rainfall runoff does not increase due to the development- the M11 was built before this.
One possibility in engineering terms is in fact a balancing pond on the stream course either directly to the west of the M11 or between the M11 and the city boundary. Here the stream is rather anonymous, more like a deep ditch, in agricultural land or close to the Barton road. This could be made purposefully deeper to create a permanent wildlife lake, fed by the stream, thereby enhancing this whole area. Such solutions are encouraged by the Environment Agency.
Response sent to Cambridge Evening News Following Interesting Article in Tuesday's Paper about the Possibility of a Countrypark between Coton and Barton (I have a copy of this article if anyone wants to see it)
A particular benefit of the proposed location for the park is that it is within walking distance from the centre of Cambridge, via the Coton footpath or the Wimpole Way from the Barton road. In fact the latter passes through the proposed park area, with a footbridge already constructed over the M11. However this particular route is not at present very popular as it involves crossing through the middle of agricultural fields near to the Barton road. It would be a bonus if, as part of the establishment of the countryside park, the path here could be made more "user friendly", providing a route along the Wimpole Way through the park and then on to Wimpole Hall.
The article did not mention that Bin Brook passes through the area proposed for the park. This stream following the storm of 21 October last year caused flooding of a large number of houses on the Gough Way estate, in Barton and Hershel roads and very nearly caused serious flooding at Robinson College. In advance of studies by the Environment Agency, residents of Gough Way have been independently considering possible solutions to avoid this happening again. One clear possibility is the construction of a balancing pond on Bin Brook either to the west of the M11- in fact it now appears this would be within or close to the area of the proposed park- or between the M11 and the city boundary. A first estimate has indicated a pond of about 1.5 hectares (say 150m x 100m) area may be adequate and it could be purposefully be made up to 3 m deeper to provide a permanent wildlife lake fed by the perennial flow in Bin Brook. It would be interesting to know the Cambridge Preservation Society's views on such a lake in or close to their proposed park.