Crenellated Pond

Where land meets water there is a narrow band richer than either side of it. Plants root in the shallows and fish feed along the edge. A crenellated pond is an ordinary earth pond whose shoreline has been dug into lobes and bays rather than a smooth oval, so that band runs much further around the same body of water. The pond holds no more water than it otherwise would. It simply has far more margin.

The lobes are shallow shelves cut into the rim of a basin that still has to meet the same depth, slope and catchment rules as any earth pond. Depth is what keeps one healthy: guidance asks for an average of about 1.5 to 1.8 m (5 to 6 ft), with half the basin deep enough that fish find cool, oxygenated water through hot weather. Every stretch of scalloped margin is depth given up somewhere else, so the shaping works to a budget. The pond also needs a catchment, meaning the ground that sheds rain into it, of ten to twenty times its own water surface. Shaping an undulating bank that stays stable is machine work with grading judgement behind it.

Plants in the shallows are the point here rather than a problem, but only within a band: cover of about 35 to 80 percent of the shallow area supports the most fish, while denser stands slow them down and yield many small ones. Cattail and water primrose colonise exactly the depth the lobes create, and left alone they close the bays over and turn the pond into a marsh. Thick floating mats also strip the oxygen from the water beneath them. Clearing is done while the growth is young, once the water warms to around 21 °C (70 °F), taking the roots rather than the tops, and only a fifth to a quarter of the affected area at a time so the rotting material does not take the oxygen with it. The necks between lobes are the thinnest soil in the structure, and narrow bays are hard to reach with any tool, which is how a yearly job gets skipped.