Consult with Environment Agency (or equivalent outside England), water authority and local planning authority as necessary. Any abstraction from water bodies, water courses or underground sources requires an abstraction licence from the Environment Agency (or equivalent).
Predicting future water supplies by gauging existing flows from watercourses and underground sources has become increasingly difficult over the last few years in Britain. Long periods of drought in many areas have caused lowering of water tables and great reductions in flows in streams and rivers. Abstraction from ground water supplies has increased to compensate. DIY methods of flow-gauging and predicting long term supplies have become virtually meaningless in the face of these uncertainties, and advice should be sought from the Environment Agency (or equivalent) for any project which involves abstraction of water supplies.
Mains water
Ponds with artificial linings by their very nature are usually in ‘dry’ areas, where the water table is relatively low, and there are no surface streams or underground springs. Where near enough to a mains supply, they can be filled with mains water, provided hose-pipe bans are not in force. They are then replenished naturally from rainwater and some run-off, together with topping up from the mains as necessary. For ponds without a convenient mains supply, the local fire brigade may be willing to help with initial filling, and if any pumping out is required. The army or the Environment Agency may also be able to assist.
Ponds newly-filled with mains water should be left for several days for the chlorine to evaporate, before plants or other organisms are introduced. Similarly, mains water used to top up existing ponds should be left in open containers for 48 hours before emptying into the pond. It may be worth constructing a small feeder pool, in which mains water is stored for a couple of days, before it is let into the main pond. Topping up from mains supply may become more difficult due to hose-pipe bans in various parts of the country. Note that ponds containing fish can be topped up and re-oxygenated with a hose-pipe even where bans are in force, as fish are classified as livestock.
The normal procedure with butyl-lined ponds is to spread the soil layer over the liner before the pond is filled with water. The soil layer is essential for aquatic and marginal plants to root into. Lay the end of the hose over a large piece of polythene, to which a string is tied for later retrieval, to prevent the water disturbing the soil layer.
Newly-made concrete lined pools need special filling techniques, to remove harmful solutes. To prevent these solutes becoming locked into the soil layer, the soil should be added only when the water quality is suitable. Shovel the soil layer over the surface of the water and allow a few days for settling before plants are introduced.
Rainwater
Some ponds are true ‘dew’ ponds, filled by rain alone without the aid of runoff. The construction of artificial dew ponds is discussed here.
Surface runoff
Rainwater runoff from pavements, roads and other hard surfaced areas will be polluted to some degree with petrol and oil residues from traffic, dog faeces, and from other debris and waste materials. On new large-scale building developments, balancing ponds are constructed at the beginning of the development stage in order to collect surface runoff, which can be very muddy and laden with silt and impurities during the building phase. These are then normally filled in, and all future runoff goes into the surface drainage system. As a better alternative, the balancing pond can be retained and planted with reeds and other plants which absorb pollutants, with the purified water feeding into an amenity lake. This can be done on a smaller scale, gathering the runoff from roads, car- parks and other hard surfaced areas for example within a school site, and diverting them into a balancing pond planted with reeds and other marginals, feeding an area of more open water as desired. Treatment of polluted runoff is a major problem for the water authorities, who should be supportive of any system which reduces the load of pollutants.
Rainwater from roofs
Rainwater gathered from roofs is a useful and environmentally sound supply for ponds. It avoids channelling rainwater into drains, and allows the more natural use of it as open water, seeping into the ground, or evaporating back into the air. Using rainwater supplies allows changeover and aeration of water within the pond. Rainwater can be used for small permanent artificial ponds, or to fill seasonal temporary pools and scrapes.
Depending on the catchment area of the roof, it may be a good idea to arrange the supply so that storm flows do not run directly in the marsh or pond, which can be detrimental to the pond ecosystem, especially in spring or summer. One method is to run the downpipe into a water butt, which has a top overflow and a bottom on/off outlet as shown. During dry weather, stored water can be run off through the bottom outlet as required. This will then give storage room for subsequent rainfall and act as a buffer against storm flows. During ‘normal’ rainfall, the overflow gives a fairly steady supply of water to the pond.
Water butts or tanks can also be used with rain diverters (available from garden centres), which automatically divert the overflow back into the downpipe and the existing drainage system. Seepage hoses or perforated pipes are another useful material, which can be laid into marshy areas so that the flow is spread through the marsh.
Alternative methods of intercepting roof drainage are shown below, in outline only.
Waste water and sewage
The treatment of domestic wastes and commercial pollutants through reedbed systems has been developed fairly rapidly over the last decade, by groups varying from alternative lifestyle enthusiasts to major businesses. For domestic sewage systems, the method is very cost- effective for small villages, holiday developments and isolated dwellings not on mains drainage. Domestic waste water can be classified as ‘grey water ’, which is waste from baths, sinks and washing machines, and sewage from toilets. All this waste matter can be treated through reedbed systems, discharging as clean water which can feed into ponds or watercourses.
Natural ponds
In areas with a permanently high water table, any excavation in the ground will fill with water to the level of the water table. However, even for ‘permanent’ high water tables, the level will alter from season and season, and year to year. Areas with a permanent high water table are easily recognised as peat bogs, damp grassland and damp woodland, and are likely to already have some open water. ‘Perched’ water tables, where clay overlays gravel or other permeable strata can be misleading. The ground may appear damp, but any excavation which goes through the clay layer will result in water being lost into the permeable strata below.
Temporary ponds in areas with a seasonally high water table can be made by excavating shallow depressions. In grassland areas, these will usually remain vegetated with grass and perennial herbs, with some areas of bare ground supporting annuals during the summer. In shaded woodland areas, a woodland flora will develop, with areas of bare ground.
Groundwater levels can be assessed by digging a trial hole or dip well. A dip well is made by sinking two 50mm diameter pipes into the ground, about 500mm apart. Use a soil auger to make the holes. One pipe should reach to the proposed full depth of the pond, and the other to half that depth. Pack tightly around each pipe with clay. Several dip wells can be spaced over the area of the excavation.
By monitoring of relative levels in the pipes, movement of water in the ground at depth and near the surface can be assessed.
For further details on dip wells and other methods of monitoring ground water levels see Burgess, Neil D and Hirons, Graham JM (1990).
Any excavation is best done during spells of dry weather, to prevent ground damage by machinery. The operator should check the ground conditions before work starts, to lessen the chance of machines getting stuck.
The quality of the water will depend on the land use surrounding the pond. The water should be purified of pollutants as it filters through the subsoil, but ponds in areas of arable farmland may have high levels of nitrites from fertilisers.
Springs
Spring-fed ponds occur naturally where water rises at a ‘spring line’, which is where permeable rock such as chalk overlays clay or other impermeable strata.
On-stream ponds
These are ponds directly fed from surface streams, and made by excavating or damming the stream. This may seem a straightforward method of supply, but there are various problems associated with on-stream supply. On-stream ponds take the flow from the catchment of the stream, and need primary outflows and spillways for storm flows.
The feeder stream, especially when in flood, will bring down suspended matter which causes siltation and turbidity. A silt trap may be needed. The dam must be sited on stable, homogenous terrain with an impermeable substrate, to avoid erosion below the dam undermining it.
For these reasons, on-stream ponds are not usually recommended for volunteer work. However, very small stream flows, which do not include storm flows from catchment areas, can be used for pond supply. These are similar to supplies from springs.
Off-stream ponds
Off-stream ponds can be excavated near streams and supplied by feeder channels, which avoids the problems outlined above. The pond is excavated near the stream, and the spoil banked up as shown.
The feeder channel can be constructed in one of the following three ways.
- The simplest feeder is a channel with sloping sides cut through the embankment. By making the channel double back, the rate of silting should be slowed. A discharge apron of turf or stone pitching will prevent scouring.
- The more usual method is to build a sluice with a silt trap on the feeder channel. When used with another sluice on the main stream, the supply of water can be controlled despite variations in flow. An overflow channel should also be fitted with a weir set at high water level to prevent the embankment being overtopped during storm flows.
- Alternatively, the overflow weir and pipe can be fitted as shown.
Larger channels or feeder pipes should have the type of concrete headwall or apron shown below. The diagram also shows how to take a feeder channel through a raised embankment by means of a sealed pipe provided with anti-seepage collars.
If a pipe is used along part or all of the feeder, it must be big enough to take normal flows and should be protected at the upper end by an open inlet of the type shown here.
An on-stream pond can sometimes be converted by diverting the feeder stream around the outside of the pond. The advantages are that siltation and turbidity problems are largely solved, and that the storm overflow of the on-stream dam need not be maintained after conversion. The new inflow should be regulated as discussed for off-stream ponds.
