Results - Witcombe Bottom



Witcombe Bottom. A level area drained by Witcombe Bottom Main Drain which is pumped into the Yeo. It is all grassland serving a large dairy at Wicombe Farm

Home > Results > Witcombe Bottom

Witcombe Bottom and the River Yeo

Witcombe Bottom is a large area of grassland in the neighbouring parish of Ash. It is home to a large intensive growing dairy farm of more than 1000 head. The output of almost all the farms in Ash and Martock is geared to supporting the dairy and the slurry is fed back onto the farms. For this reason the survey was extended northwards to include this area. High levels of phosphate were found in all streams and ditches tested and in the river Yeo.

Two sewage treatment works discharge into the area. The plant at Ilchester includes phophate removal and was foud to have no affect on the Yeo levels. The small works serving Tintinhull, discharges indirectly into the Witcome Main Drain; its impact could not be tested.


The Main Observations

1 The origin of phosphate in this system is almost all agricultural
The main agricultural enterprise in this area is Witcombe Dairy, and the greater part of the agricultural land in this area, and in the two Parishes of Ash and Martock, is dedicated to supplying fodder, in various forms but mainly grass, to the dairy. The grass is fertilised mainly by slurry.

2 The phosphate level in all samples was Poor or Bad.
All ditches tested were classified as Poor or Bad
with a phospate level up to 100x the normal stable level. The area is a major contributor to the poor state of the Yeo, and thence the Parrett, at Langport.

3 The main crop is cultivated grass.
Almost all the fields, other than those closest to the Yeo which regularly flood, are planted with fast-growing grass fed with slurry and cropped several times a year for the dairy. Many fields have been greatly enlarged by hedge removal.

4 None of the fields cultivated for grass, or any other crop, had field margins that met DEFRA standards.
All fields were cultivated to the hedgerows. There was evidence in a small minority of fields of a small margin on which slurry was not applied but in all cases this was less than 6m. Every one of the field edge ditches tested for phosphate showed Poor or Bad water quality. One, flowing into Witcombe Main Drain, showed readings up to 2.9ppm, over 100x the normal stable level.

5 Poaching of the Yeo and the Main Drain is widespread
The large area of grassland adjoining the Yeo and enclosing Witcombe Bottom Main Drain has no mechanism to prevent poaching (trampling and feeding) of the watercourse banks. Cattle, up to 200 head, freely graze the riperian plants and drink from the the Main Drain. This is in marked contast to the north bank of then Yeo where livestock is restrained by electric fences. The biodiversity difference between the two banks is striking.

6 Witcombe Main Drain is consistantly heaily polluted
All the rhynes in the area drain into Witcombe Main Drain which has a high phosphate concentration consistemtly around 0.8pmm independent of water depth.. Because the water moves, usually daily, when Long Load pumps are on, summer algal blooms only occur downstream of stands of reed or waterlilies where the flow is impeded. Both banks are heavily poached along their whole length.

7 Phosphate levels in the Yeo show a seasonal variation
There is evidence of a seasonal variation which will be studied further. A complicating factor is the difference between summer and winter drainage protocols which means a reversal of the flow in some channels. Because of the large difference in normal water volume between summer and winter a varialtion in concentration is expected.

8 Ponds in the area may be largely free of phosphate
There are several ponds in
the area dedicated in the main apparently to seasonal wildfowl sporting. All appear to be retention ponds that are topped up from the rhynes when in spate. There does not appear to be a through flow but this has not been fully researched on the ground. One pond only was tested and showed a low level of phosphate contamination. Pond vegetation removes the phosphate from the trapped water.

9 Ilchester Sewage Treatment Works
No additional phosphate was detected below the outflow into the Yeo from Ilchester Sewage Treatment Works where Wessex Water has installed a phosphate removeal stage.


Download the full Witcombe data here, xlsx file

Survey scale used


<0.04 ppm
0.04-0.07 ppm
0.08-0.19 ppm
0.20-1.00 ppm
>1.00 ppm

This scale is adapted from recommendations of the UK Technical Advisory Group of the Water Framework Directive (Phosphorus Standards for Rivers, 2013)

Data Map
A data map showing he location of all measurements is here




Witcombe grass Main Drain

A typical Whitcombe field showing cultivated grass to the field edge adjacent to a sustantial ditch

Whitcombe Bottom Main Drain showing extensive poaching and grazing of riperian plants by typically 80-100 head of cattle on each bank

Yeo Long Load Ditch

The River Yeo looking upstream. Wilcombe Main Drain is just of view to the right. The difference in biodiversity between the two banks is striking with a rich mix of flowering plants left (north) and grazing and poaching to the waters edge on the right by around 80 head of cattle. Livestock on the north bank are restricted by an electric fence.

Looking south along the hedge that separates the gardens of Long Load from Whitcombe Bottom. The ditch to the right is deep and free flowing in all weathers and had a phosphate concentration of nearly 3ppm (July21), about 100x normal. This field margin was ploughed and planted with fast growing grass in 2020 and is used as a drove to take cattle to and from the field between the River Yeo and Whitcombe Main Drain. It is poached and grazed along its whole length.