South East Rivers Trust regarding Chafford Lane Sluice

 

Chafford Lane sluice, River Medway; an opportunity to restore river habitats?

 

Chafford Lane tilting sluice is an Environment Agency owned structure on the River Medway, which supports an approx. 3-4 kms of impounded river upstream. The impoundment degrades the river habitat in this upstream reach, creating a lowland type river environment in what would naturally be a riffle-pool sequence and presents a complete barrier to fish migration.

Humans have adapted rivers for our own use, modifying them to facilitate land use for agriculture and development, navigation, water supply, power generation and other priorities. Fish and other wildlife evolved in and around rivers before humans had this influence and are therefore not adapted to the modifications we have made. One particular relic of our industrial past are watermills that used moving water as a power source, harnessed by a water wheel or water turbine to drive a mechanical process such as milling (grinding), rolling, or hammering. Such processes were used in the production of many goods, including flour, timber, paper, textiles, and many metal products. At Chafford Lane there used to be a corn mill and later a paper mill, milling here dates back to at least the thirteen century, so the site has significant heritage value.

Watermills impound the river upstream and use this stored water as a power source during operation. However, structures such as mills, weirs etc. impact rivers in two main ways; 1. Habitat fragmentation which disrupt the continuity of habitats used by wildlife and is a terrestrial conservation issue as well as an aquatic one. Habitats which were once continuous become divided into separate fragments, restricting the movements of organisms (e.g. fish) and separating them from habitats / resources / other organisms required for their survival / the completion of their life-cycle. Fragmented habitats are also less resilient, preventing re-colonisation after pollution incidents and lowering genetic variability, due to the restricted effective population size, potentially placing populations at an evolutionary disadvantage. 2. River habitat is degraded by the creation of an impounded reach upstream (river-like habitats become lake-like) drowning out natural features like riffles, causing important spawning and nursery habitats for river fishes to be lost, thus lowering recruitment and breeding success. Also, natural processes such as sediment transport are prevented. Rivers are naturally dynamic with erosion and deposition occurring in balance, creating a highly varied mosaic of micro-habitats for all life-stages of fishes. Weirs arrest this natural tendency for change, creating a uniform static environment. Upstream an over deep river channel akin to a lowland river is formed in the impounded reach, which may be inappropriate for the fish community (for instance, barbel habitat may become bream habitat). Impoundments also alter the temperature regime, oxygen content and cause siltation in the upstream reach. More information can be found here:

http://www.southeastriverstrust.org/how-weirs-affect-fish-communities/

 

The sluice structure at Chafford Lane no longer servers a purpose and as such is a redundant structure. Being a number of years old, the sluice is beginning to degrade and because it serves no purpose, is unlikely to be renovated. Due to this, a course of action is needed to ensure a safe and secure long term future for the site and there is an opportunity to remove or reduce the upstream impoundment, which will help restore this river habitat and provide benefits for fish and wildlife.

 

However, the upstream impoundment may be valued by some river users / local residents, so a compromise position between complete removal and the status quo maybe required. The South East Rivers Trust (SERT), an environmental charity dedicated to conserving and restoring rivers and their catchments across the south east of England, are consulting and engaging interested stakeholders and local residents about the future of Chafford Lane sluice. As such, if you have opinion, interest or a stake in the river or the Chafford Lane sluice site, please get in touch with Dr Chris Gardner at SERT his email address is chris@southeastriverstrust.org