Assessment of Leaky Dams

 Macro-Invertebrate Ecology in West Dorset


The VCT are always keen to support new small projects that can add to our better understanding of all aspects of river ecology. Support therefore was given to a project in Dorset led by Dr Dominic Stubbing. This has involved applying a well known method of holding back water by the introduction and enhancement of woody debris into the very top headwaters of a small river catchment. The River Asker was chosen as there was already an existing group of trained  volunteers willing to help with the detailed invertebrate monitoring. This would be necessary in establishing the value of such structures over a period of time and further our understanding of how such dam structures, whether natural or introduced, can really benefit the ecology of the very upper catchment of a river.

Aug 2023, Dominic Stubbing

The latest report is an Assessment of man-made leaky dams’ contribution to macro-invertebrate ecology in a West Dorset stream. You can read the full report here.


Nov 2022, Dominic Stubbing

The first set of sampling was completed in September and went very well. Initially, macroinvertebrates samples and other recording took time to fine tune but the results have meant a good protocol. Now that has been completed, a better picture of the overall plan ensures improvements. The funding was not confirmed at that point and when it was this led to the orchestration of the second sampling period in November, which also went well.

Overgrown built dam on Askerswell stream

The overall plan now looks like a sample in late January would be the next best time slot. This means two spring samples could be conducted which is best. This means four out of the five periods are in the best time windows for sampling macro-invertebrates. This maybe adjusted to fit funding. The number of built structures being sampled is six and natural dams six. Three built dams and three natural dams are on the Loders stream and the other six on the Askerswell stream. Other parameters recorded are debris and flow measures.

The samples taken are giving a sensible number of individuals in samples to account for variation and enable on-site counting. Also, the species and families recorded are interesting and what you might expect. They are also showing in the different habitats as you might expect. Those habitats are then related to the dams and their impact on habitats, which looks to give a nice story. Data is being processed at the moment.

Field sampling materials

Images anti-clockwise:  Overgrown built dam on Askerswell stream, Stonefly, Field sampling materials.

Our Other Projects…

Riverfly Monitoring Initiative

Riverfly Monitoring Initiative

The Riverfly Partnership runs an invertebrate monitoring scheme which is of keen interest to anglers and wildlife enthusiasts alike who share a concern for the present and future health of our rivers. The initiative is based on the counting at regular intervals of key river insect species and other invertebrate groups as a method of assessing river quality.

Tree Sparrow

Tree Sparrow Project

The Tree Sparrow is synonymous with mixed farming landscapes and was once widespread across Wiltshire and Hampshire, but are all but lost as a breeding species in the latter. Changes to agriculture and the loss of nesting sites have driven the population’s decline, although significant efforts have been exerted in Wiltshire to help their recovery.