Witcombe data map

Witcombe bottom data map

This area is within Ash Parish and drains into the river Yeo. It is included in the survey as the great majority of the farms in both parishes sustain the large dairy at Witcombe by producing crops for the herd, in many cases by direct leasing. This in effect makes the two parishes a single environmental unit

This is an area that is heavily contaiminated by phophate; all the samples except one (an interesting exception discussed below) are either Poor or Bad

Map Legend

Data
Download the full Yeo (Witcombe) data

Discussion

The River Yeo
The River Yeo has a consistently high phophate concentration summer and winter. There is a barrier at Long Load which is raised in summer to retain water upstream for agricultural use. Raising the Long Load barrier for the summer level seems to have little impact on the phosphate concentration although because the volume increases much more phosphate is retained upstream.

Ilchester Sewage Treament Works
Ilchester Sewage Treament Works has an outflow into the Yeo adjacent to the A303 bridge. No additional phosphate was detected downstream of this outflow. the Ilchester plat is listed as having a phosphate removal stage (Two eadings above (Y19, 0.40ppm) and below (Y18, 0.41ppm) Ilchester STW show no significant change due to the outflow)

Witcombe Bottom Main Drain
Witcombe Bottom Main Drain collects water from the whole of the Witcombe side of Foldhill through a complex series of rhynes though which water often flows both ways according to season. The Main Drain was tested several times just uptream of the pumping station, twice in the winter season (Y5, 0.50 pump off and Y4, 0.8ppm pump on) and twice in the summer season when the Drain was substantially fuller and not being pumped as much (Y17, 0.28ppm, Y22, 1.24ppm).

The much higher summer measurements show not only a concentration increase but are taken from a much higher volume as pumping is reduced. Together this represents an increase in phosphate mass of possibly as much as tenfold. The source of phosphate in the summer is not only the tributary rhynes but direct cattle urine during the considerable riparian poaching by a herd numbering as much as 200 (which will produce collectively around 5kg of phosphate per day in their urine)

In winter, the Main Drain is pumped when necessary, automatically, into the Yeo. Because the concentration and also the volume in the Main Drain is usually high, the process of pumping raised the phosphate concentration in the Yeo–by about 25% on the March day when recorded (Y3, 3March, 0.51ppm, pump on, Y1, 4March., 0.41ppm, pump off).

Witcombe Rhynes.
The inflow into the Drain is mainly from field run-off and also from Tintinhull Sewage Treatment Plant which is not one listed as having a phosphate removal stage. It has not been possible to test the outflow as it is on private land.

Several rhynes were tested in the Witcombe area. All showed a high level of phosphate, some very high. Most of the testing was done during the spring slurry-spreading season. One stream showed a consistently very high phosphate load (Y11, 3March, 1.01ppm, Y16, 1May, 1.82ppm, 12July 2.92ppm). This ditch is free flowing throughout the year and is adjacent to a margin that has been recently ploughed and sown with fast-growing grass. It is used as a drove to move cattle to the northern part of the field between the Main Drain and the River Yeo. It is much poached.

All the fields in the area, other than those at the Boitom which regularly flood, were farmed for rye grass. No field margins were left uncultivated and evidence of slurry spreading was noted up to the edges.

Pond
The area has several ponds for sporting use. These generally do not have a through supply of water and fill up during wet periods. They have a rich mix of edge plants and some bog areas. One was tested (Y10, 0.02ppm) and found to be free of phosphate when the nearby ditch which feeds it was heavily contaminated. This pattern has been observed with all such ponds in the study.