A dew pond is a man-made water reservoir, often found on the high chalk downs and hills of southern England. These ponds are intriguing due to their historical reputation for collecting and retaining water even in dry conditions on elevated ground. They represent an ingenious solution for farmers seeking a reliable water supply where natural sources are scarce.
Defining the High-Ground Pond
Dew ponds are artificial, shallow basins constructed on elevated landscapes with highly porous underlying geology, such as the chalk uplands of the South Downs. Because the bedrock contains numerous small fissures, rainwater quickly drains away, leaving the high ground without natural surface water supplies. These ponds were designed to overcome this geographical limitation, establishing a water source for grazing livestock, primarily sheep and cattle. The typical dew pond is saucer-shaped and circular, often measuring between 30 and 70 feet across, though its depth rarely exceeds three or four feet.
How Dew Ponds Actually Collect Water
The name “dew pond” is largely a misnomer, as the majority of the water collected comes from precipitation rather than dew itself. Scientific study confirms that the amount of moisture contributed by dew is minor compared to the total volume provided by rainfall, mist, or fog drip. The pond’s success lies in its thermal properties and its ability to maximize the capture of atmospheric moisture while minimizing water loss through evaporation.
The construction is engineered to keep the water temperature lower than the surrounding ground and air, a process known as thermal inertia. This cooler water surface reduces the rate of evaporation, which is a major source of water loss on exposed hilltops. The large, shallow surface area is designed to capture a significant amount of direct rainfall. The pond’s raised rim and surrounding margin also act as a small catchment area, directing surface runoff into the basin.
Traditional Construction Methods
The construction of a traditional dew pond focused on creating an impermeable basin on porous ground. The process began with the excavation of a shallow, saucer-shaped depression lined with several distinct layers. A base layer of insulating material, such as straw or ash, was laid down first to prevent heat transfer from the earth below.
This insulating layer was covered by a thick layer of puddled clay or marl. The clay was wetted and compacted to create a dense, watertight seal that prevented water from seeping into the permeable ground. Lime or soot was sometimes mixed into the clay to deter earthworms, which could compromise the seal. A final layer of chalk rubble, stone, or gravel was spread over the clay to protect the lining from livestock hooves and from the sun, which could cause cracking.
Historical Use and Current Status
Dew ponds played a significant role in enabling upland farming, particularly in the chalk downlands, before the advent of modern water pumping and piping technology. They provided a consistent, localized source of water necessary for the successful management of large flocks of sheep on dry pastures. The ponds allowed for continuous grazing in areas that would otherwise be unusable for livestock during dry seasons.
Today, the utilitarian need for new dew ponds has diminished due to modern infrastructure supplying water to farms. Consequently, many historical dew ponds have fallen into disrepair or have been abandoned. However, a significant number of these structures are now valued for their cultural heritage and ecological function. Maintained ponds serve as important, isolated habitats for various wildlife, including amphibians, insects, and migrating birds, acting as protected oases in the dry upland environment.