An underground river

Parts of the River Frome in Gloucestershire have dried out completely in the last couple of weeks. We’ve had a few reports from people concerned about what’s caused it and whether it will return to its former glory. Here are some answers.

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Not all of the river is affected, but a fair stretch to the east of Stroud, in the Frampton Mansell area is now completely dry.

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The drying out is a completely natural phenomenon. It happens most years, and is the result of the local geology.

The River Frome flows over highly permeable (porous) rock formations such as limestone and sandstones which also make up the principal aquifers in the Stroud area. Aquifers are underground water reserves, bound up within rock formations. Also, in its upper reaches, the River is mainly groundwater fed. As the groundwater table declines in dry periods below the bed of the river it experiences the drying out episodes which we are seeing now. Any flowing water is now beneath the surface! Extensive faulting (cracks and gaps in the rocks) in the area also locally contributes to losses of river water into the underlying bedrock via these features.

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When we get some rain the groundwater level will rise back to the surface and the River will reappear.

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Because the process happens quite slowly fish and insects tend to naturally move away from the drying area and then return once flows return.

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Fry-ing tonight!

Our Environmental Monitoring teams have begun fry surveys on the River Severn. First up were three sites around Shrewsbury one upstream at the County Showground, one in town at Pengwern boat club and one downstream at Monkmoor.

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We use a 25m micromesh seine net to catch fish fry from the edge of the river. We then measure the first 50 fish of each species to get a size range and then collected a total count. At all three sites sampled there was a good range of fry caught in large numbers.

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Species caught included chub, dace, roach, gudgeon, barbel (pic below) ruffe, bleak, Atlantic salmon, minnows, sticklebacks, bullheads and stoneloach.

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This work, which is funded through the money we receive from fishing licence money, is part of a bigger project investigating fish populations on the main River Severn.