Water management in humid climates

There are several tools that we use in permaculture for water management in humid landscapes, but the main one is systems of ponds with connected swales. This system is only viable on flat land, or on slopes less steep than 20%. This system captures and pacifies water flows and soaks them into the landscape. The water soaked into the ground by a swale forms an underground pool of water that moves extremely slowly downhill. A swale consists of several parts: The swale, the uncompacted berm, which is just downhill of the swale itself, formed out of the soil from the swale, and the treed ecosystem that the swale supports, which is planted on the berm of the swale, and just downhill from it. The swale is installed on contour with a perfectly level bottom, allowing water to spread right across the landscape, equally benefitting valleys and ridges. Over a seven year period, the underground pool of water gets bigger until it starts recharging aquifers, or hits an impermeable clay layer, rises to the surface and creates springs. Either way, the hydrology of the greater landscapes greatly benefits in the long term from the installation of swales.

Swales are fundamentally tree-growing systems. They deliver water directly to the tree roots, where it is most useful, and safe from evaporation. Having well-hydrated subsoil and trees to access this underground irrigation water can save a farm from drought. On-contour swales are often used in connection to on-slope ponds. The swales capture water, and the excess passively fills the ponds that the swales are connected to. Pond liners are not advisable. The best method of building ponds on slope is probably the compacted clay dam. These ponds are excellent for providing water to livestock, irrigating crops and providing a place to do aquaculture.

On mostly flat land, very large water storages can sometimes be created for very little cost. You have a lot more creativity available to you here, because you are less confined by the necessities of working on a significant slope. There are some extremely productive systems that can be installed here.

On slopes steeper than 20%, swales become dangerous, ponds become impractical and different water management methods are required, such as sloped terraces, or clumping grasses such as Pampas planted on contour. The plantings on contour without a proper swale still create a local increase in soil moisture, and decrease the local effect of the wind. This can help young trees to get established, and stabilize the slope.