Streams at normal flow are not a problem but when in spate, they carry water and sediment fast down the system. Result: flooding and ecological damage.
Where upland areas and streams have been degraded, run off is also accelerated. The primary aim of leaky dams is to slow the flow in spate conditions and protect what's downstream.
Building the dams from locally sourced logs means low transport costs and creates opportunities for clearings where re-growth can begin, thus contributing to a multi-level tree canopy.
Planning is crucial to getting them in the right place and a site assessment and permit from the Environment Agency for work to ordinary watercourses is a legal requirement so there is some preliminary form filling and possible site inspections to do before anyone can begin any work on a watercourse.
Here are photographs take during work by Bradford MDC and the Environment Agency at Deep Cliff Hole, Harden, West Yorkshire in March 2019
Logs are dragged in, by horse in this instance, to a notch across the stream.
... and pinned into place with brash to help it blend in to the landscape a bit.At this site, there are several such dams along a 100m stream.
