This will be the first of two posts on the use and practice of using dipwells at Fleet Pond.
Colin Gray writes:
The use of dipwells has been a recommended practice for sites where water levels vary significantly or where drainage has had (or is perceived to have had) adverse affects on the soils.
We have been gathering data since 1995 for the nine dipwells (see map below) and six water level gauges (most of the gauges came later in 1998 as there was only one prior to that year).
A dipwell is basically a length of plastic pipe with holes drilled in the side, driven as far as possible into the ground (see picture at top). At Fleet Pond the underlying gravel prevents very deep penetration, but the deepest goes down to about 1m below soil level. That is adequate as the water table is very high in the area. Each week the measurements are converted to cm above or below soil level. When our botanical surveys are conducted (each two years or so) any recorded changes can be compared to variations in water level. Thus, for example, the recorded dry years have seen an increase of bramble in the wetland areas – not a plant one would usually see in a marsh. Other plants can move in if levels remain low for longer periods. Birch and oak for example, not trees that would usually survive with their roots in water.
We have to put a cap on each dipwell to stop small mammals falling and drowning and the better dipwells also have a sealed base to stop silt rising to fill the well.
The rangers installed dipwells on Elvetham Heath Local Nature Reserve but many were vandalised and the rangers found they had not enough time to measure them regularly so the practice there died out.
Other sites do use them where water plays a significant role in the diversity of plants and particularly if it is important to maintain a certain level of soil saturation to protect a rare or endangered plant or invertebrate.