Agenda item number: 5 (Appendix 10)

Water level management along the and Godalming Navigations

Water control and weir keeping

There are 30 regulating weirs or structures along the navigations:

 9 National Trust (including 2 flood gates and 1 lock adapted for flood alleviation)  11 Environment Agency  10 Privately owned.

The objective of water control is, depending upon factors such as time of year, saturation of soil, level of the water table and current weather conditions, to slowly and in a managed manner release water down through the river system to the . Once all weir gates are fully open if the river level is still rising it is probably that flooding will occur when the capacity of the river channel is no longer large enough to contain the volume of water flowing through the river.

The Lengthsman Team operate twenty three regulating structures along the Wey: - nine sets of Environment Agency weirs for flood relief, five privately owned structures and 9 Trust structures (including 2 flood locks and 1 adapted lock). Weir keeping is a most important part of a Lengthsman’s job. They are responsible during normal, increasing and decreasing river flows for maintaining levels in their length of navigation. The Lengthsman records all adjustments made to weir gates and they telephone their colleagues operating adjacent weirs to advise them that the water will be rising or falling.

The Lengthsmen are supported by a Mobile River Warden, who provides annual leave cover, and by Seasonal Relief Weir Keepers during periods of flood and high flows necessitating extended weir operating hours. There is one set of weirs operated by a contractor on behalf of the Trust. It is the role of the Head Lengthsman to co-ordinate all of these weir operators to ensure that the levels are managed. The Environment Agency has responsibility for fluvial flood risk management from Main Rivers such as the River Wey. The National Trust operates EA weirs under contract and the Head Lengthsman has a close working relationship with EA officers.

Water levels along the Navigations are affected by different factors. For example, in heavily built up areas like Guildford, surface water running off the roads and car parks can contribute to rising water levels. In other areas tributary streams to the Wey such as, Waters and Tillingbourne at Shalford, or the Hoe Stream at Pyrford, all add flow to the Wey Navigation. During flood conditions, it takes some time for rainwater to discharge into the river system and for changes in water level to work their way downstream. A rise in water level at Godalming can take up to thirty hours or more before it is felt at Weybridge.

Each set of weirs are different and the local Lengthsman must know what factors can cause a change in his levels, and how the operation of his weir will affect his length of river. Water levels can rise and fall very rapidly and the Lengthsmen need to keep a very close check on the level of the river, in case they need to adjust their weirs. During periods of high rainfall, checks need to be made every two hours, morning and night. Christmas Day and New Year are no exceptions and over the last few winters, the Lengthsmen have been very busy over the holiday period.

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Agenda item number: 5 (Appendix 11)

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