Case Study: University of Surrey
The Problem: -
Two lakes exist at the University; one large lake formerly used as part of a water cooling system has a pump installed that pushes water to the top second lake by way of a powerful aeration fountain. The top pond also receives a variable volume of rain water from the University roofs. The stream channel links the two water bodies and allows the water to flow from the top lake back to the bottom lake. Unfortunately the stream channel had seen little or no real silt management or bank-side maintenance for many years leading to heavy silt deposition within the stream. This effectively made the stream shallower and the increased water velocity began eroding marginal soil making the stream channels even wider and shallower. Un-wanted emergent aquatic plant species quickly colonised the shallow stream channels causing the water flow to reduce further which compounded the silt deposition problem.
Burley Aquatic Developments proposed and employed a bio-engineered methodology whereby coir rolls pre-planted with native marginal aquatic plants were used to narrow the channels thereby creating greater channel water velocity and a variable scour effect dependant upon seasonal water flow. Once the coir rolls were fixed in place a volume of silt removed from the channel was used to backfill behind the coir rolls firming up the old undercut bank-side margins. These planted coir rolls will quickly establish and beginning binding the new bank-side soil behind the coir rolls and provide an excellent show of native marginal aquatic plants each year.
A little silt management will still be required every 2-3 years and yearly stream bed aquatic foliage control is a yearly maintenance requirement to ensure that the stream channel remains clear of impediment and looks its best every year.