The Yeo from Ilchester to Langport



Witcombe bottom
Witcombe Bottom Main Drain in a morning spring mist. All the rhynes for two kilometres upstream of Long Load drain into this. It is pumped automatically into the Yeo at Long Load Pumping Station. Very variable phosphate concentration, 0.2 to 1.2 ppm

Home - 2022 Data - Yeo

Witcombe Bottom and Wetmoor
This survey covers two Moors on the south bank of the Yeo; Witcombe Bottom upstream of Long Load Bridge and and Wetmoor downstream. Wetmoor (actually three linked moors, Outmoor, Wetmoor and Whitmoor) is a Ramsar wetland.

Both Moors fill from streams and ditches from slightly higher ground to the south. This water accumulates after flowing through a rhyne network in two main drains, Witcombe Bottom and Long Load Main Drains. These both flow down to the slightly lower west end of each Moor where they are pumped up into the Yeo.

There are manually operated sluices that can allow water to flow onto both Moors from the Yeo if they become too dry in summer. These are opened when the Moors dry or to 'freshen' the rhynes. Essentially the water flows one way only - down to the lowest point of each moor–the north-western corner– and then up into theraised river Yeo through pumps.


Witcombe Bottom hydrology

Witcombe hydrology

Water entering the Witcombe Bottom Moor comes from the higher land to the south. It eventually flows into Witcombe Main Drain in Witcombe Bottom from where it is automatically pumped up into the Yeo at regular intervals. In normal operation, no water from the Yeo enters this Moor

Data Map
A map showing sample details for both Witcombe and Wetmoor is shown here. Zoom in and click on a sample to show data

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Map legendMap Legend

The phosphate concentration in the Yeo has consistently remained around 0.4 to 0.5 ppm for the last year. The concentration of phosphate in the Main Drain at Witcombe Bottom is variable and dependent on the two sources. One source, however, Tintinhull STW, has a roughly constant outflow and hence the variability is likely due to Witcombe Dairy, a large enclosed unit producing seasonally variable concentrations of phosphate in several rhynes.

The rhynes further east of these two sources significantly show barely detectable phosphate.

Data File
A csv file of the data can be downloaded here. It can be viewed in Excel.

Witcombe Bottom during the summer
The dry summer saw the volume of water pumped from Witcombe Main Drain into the Yeo fall to below 30minutes per day which equates to around 1000 m3/day (see below). This compares with 30minutes in around 6 hours during avarage rain periods.

Slowing the flow rate through the Drain allowed phosphate to be absorbed during the passage of the water along the drain creating an increasingly large difference in concentration between top and bottom during the dry May such that by May 15th no phosphate was detected at the pump compared with 1.6 ppm at the top end of the Drain.

By July there was little change in the low pump flow rate but between 200 and 300 heifers were habitually poaching the bottom end of the Drain which was their only water supply. A phpsphate concentration of 2.5 ppm was recorded in the now largely stagnant water (below).

Long Load


Wetmoor hydrology

Wetmoor HydrologyWater entering Wetmoor comes mainly from slightly raised agricultural land to the south. The water flows in a series of rhynes down three levels controlled by sluices. The overall drop is a little over a metre in 5km. It eventually accumulates in Long Load Main Drain and is raised into the Yeo at Huish Pumping Station.

Water is fed onto the Moor from the Yeo from time to time via sluices near Long Load to maintain the required level and also to refresh the Moor rhynes by creating some water movement. There is some flow into the Moor from the west (west of the Muchelney-Langport road) which is fed in summer from the Parrett near Muchelney Lakes. This collects in Thorney Moor Main Drain just south of the Yeo at Langport. This joins Long Load Main Drain just before the pumps.

The volume of water flowing onto the Moor in summer from the Yeo and Parrett is very small compared with the total flow in these two main rivers (no exact figures are available).


Long Load Main Drain showed barely detectable phosphate throughout its length when the inlets are closed (winter). When the inlets are opened water wih a high phosphate level is let into the moor. Testing shows that this concentration reduces as the water spreads out through the moor rhynes. This could be caused by dilution but the evidence from spring 2022 suggests that the excessive phosphate coming from the Yeo is removed by growing plants in the rhynes and possibly also by the sediment. This mechanism is commonly observed elsewhere, most obviously in the Stourhead study and the ponds of Martock

The Thorney Drain brings water from the south w around Muchelney which in summer includes water from an inlet from the Parrett. This drain was free of phosphate in May but by July showd a concentration of around 0.8ppm, by which time the concentration in the Parrett which was feeding the Moor was very high indeed at around 2.5 ppm.


Pump outflows
The EA monitors water levels at its pumps in real time and the output is publicly available for a week.. The trace reveals when the pumps are switched on and off. This allows the daily flow rate of water from the Moor to the river to be calculated knowing the pump capacity. In normal conditions this is the smallest pump of the cluster
Huish Pump rate is (reportedly) 1.2m3/s maximum
Long Load pump is about 0.68m3/s maximum

Real time pump data
Pump data can be harvested from real time river level monitoring. Witcombe Bottom Main Drain at Long Load pump is here
Long Load Main Drain at Huish is here
River Yeo at Huish Pump is here

1 The main rivers act as drains rather than water supplies for the Moors except for dry summer periods when it is fed from three inlets, two from the Yeo and one from the Parrett.

2 The main inflow comes from nearby SSSI farmland and free of excess phosphate

3 Opening the inlets from the Parrett and Yeo in summer allowed in water with a high level of phosphate (2.5 and 0.8 ppm respectively). This was reduced to around 0.8 and 0.2 respectively as it flowed through to the pumps.

4 Knowing the flow rates, such as the rate of flow out of Witcombe Main drain permits some highly significan calculations. For example, in May 22, the flow down Witcombe Bottom was slow enough to allow natural processes to absorb around 2kg of phosphate per day. The main souces of this were Tintinhull STW and Witcombe dairy. The significance of this is that this single process is of the same order as the Entrade offset target for the whole of the Yeo catchment (0.95 tonnes/year).



Last modified 10/10/22