Storing Water in the Landscape: A Swales and Ponds Primer
Rain is one of the leading causes of soil erosion. The problem isn’t with rain itself, but rather with bad land management practices and farming practices that aren’t designed to take advantage of rainfall in a holistic manner. The best place to store water is in the landscape itself, and through the process of design, water can be effectively stored in the landscape for increased fertility, longer growing season, and reduced erosion.
Why Rain Causes Erosion
Rain will always follow the path of least resistance, and bare dirt with any sort of soil cover doesn’t offer much in the way of resistance. Even on landscapes with very little noticeable slope, heavy rains will cause erosion and the loss of top soil from the movement of water over the land.
Leaf fall, native prairies, fast growing pioneer species, and pretty much any other source of abundant organic matter will quickly grow on top of any bare patch of ground in order to protect the soil from the potentially dangerous effects of erosion from heavy rains.
Rain, however, shouldn’t be considered the culprit of erosion. Rather, our modern day farming practices are the main cause of soil erosion. By removing organic matter, tilling the soil several times each year and leaving it exposed to the elements, and spraying fields with heavy doses of toxic chemicals that destroy the soil food web, even a small thunderstorm is bound to lead to erosion.
The Landscape as a Gigantic Cistern
Modern farming, on top of being one of the main contributors to soil erosion, is also dependent on huge amounts of fresh water for irrigation. In the Midwestern United States, the Ogallala Aquifer is a huge reservoir of fresh water left over from the glacial age. In less than 100 years, Midwestern farmers who pump up tremendous amounts of water to irrigate their crops have almost completely drained one of the largest sources of fresh water in the continental United States.
Ironically, farmers rely on unsustainable water sources that are pumped up from the depths of the earth while the rain that falls directly overhead flows over their land (instead of infiltrating into it) taking away their top soil. This incongruous situation stems from bad land management practices that don’t understand how to take advantage of the abundant sources of rainwater.
Healthy soils that are covered with mulch and/or a permanent layer of organic matter are not only protected from erosion, but they have the ability to retain huge amounts of water. The water retention capacity of soils allows them to retain humidity and thus reduce the reliance on other sorts of external irrigation. Keeping the soil covered with a permanent crop cover or organic mulch material is the best way to improve the water retention capacities of the soil. Earthworks such as swales and ponds are two other ways to increase the amount of water “stored” on your land.
How to Build Swales
Since you will never be able to store all the water that falls on your site through a cistern, the best way to hold water on your land is through developing the conditions to hold water in the soil. Whereas a good-sized cistern may be able to hold 20,000 gallons of water, you can hundreds of thousands of gallons of water in the actual land itself.
Swales are on-contour ditches that are dug across your site with the purpose of stopping the flow of water in order to make the water slowly filter into the land instead of rushing over it. On contour simply means “level”. As the rain water hits the swale, it will accumulate and slowly sink into the land. On a piece of land without swales, a day or two after a good rain and the soil will begin to feel dry. With a series of swales across the landscape, however, the soil remains humid for more time because of the extra infiltration of the water provided by the swales.
Finding the contour of the land doesn´t require having specialized laser levels or complex GPS-oriented devices. The best way to find the contour of your land to know where to build the swales is through the use of a Bunyip Water Level. This simple “appropriate technology” tool can be built for about a dollar and will last you a lifetime.
To build a Bunyip water level, you´ll need two pieces of 1×1 pieces of wood about four feet high. Starting a couple of inches from the top, mark every inch (or centimeter) on the post until it resembles a long yard stick. The number “1” should begin at the top. Cut a piece of clear plastic hose about 25 feet long and connect each end to the 1×1´s with duct tape or string. Fill the plastic hose with water through suctioning it through the hose.
Now stand the water level up on level ground. If you are on completely level ground, the readings on both 1×1 posts will be the same. If one of the posts reads 18 and the other 16, then that means that one of the posts is two inches (or centimeters) higher than the other one. To find the contour of the land, two people move the posts of the water level until they have the same reading. Place a post or marker at each spot you measure aS level so that you will know where to build your swale.
When you build your swales, the earth that you remove from the ditch (between 3 and 6 inches deep) can be piled up on the downside of the ditch to create a mound or basin of raised earth. This will also help to slow erosion and keep the water in the swale as it percolates into the soil.
How to Build a Pond
There are multiple advantages to having a pond located on your site. Firstly, the water that otherwise would have left your land will now be slowly soaking into your land, increasing the moisture and fertility levels. It will also offer you a place to possibly raise fish or ducks as well as function as a reservoir for the water needs of other livestock you may be raising.
There are three steps to building a pond: digging it, “gleying” or sealing it, and filling it with water. Instead of a simple round pond, incorporating nonlinear lines in the design of your pond will increase the amount of “edge” between the water and the land. These places create what is known as the “edge effect” and are incredibly diverse niches in ecosystems that will allow you to grow a variety of crops that would otherwise not be able to be grown.
Once your pond is dug, you will need to find some way to seal it so that the water doesn’t simply drain away. Heavy plastic pond liners can be expensive, especially if you have a large pond, as can trying to create a cement pond for your pond. Though both of these options will last quite a number of years, another cheaper is to “gley” your pond with a mixture of clay and fresh animal manure.
The process of gleying a pond is basically an effort to mimic how ponds are sealed naturally in the wild but speeding up the process. You will be trying to form an anaerobic layer (absence of oxygen) in the soil at your pond´s bottom so that water can´t get through. The slimy soil found at the bottom of some ponds is an example of the natural gleying process.
First, begin the process by lightly roughing up the clay bottom of your pond with a hoe. If you have a supply of fresh animal manure, lay a layer of the manure over the clay bottom. If you can´t get animal manure, using compostable material like kitchen scraps will also work. Once the bottom of your pond is filled with animal manure or other compostable material, cover it with cardboard. Over the next two weeks maintain your pond bottom wet, but not with more than a half inch of standing water. The water will help start the gleying process of creating an anaerobic layer. After a couple of weeks, you should be set to fill up your pond.
How to Collaborate with the Rain
Instead of considering the rain to be an enemy that causes problems on your land, it is necessary to accept that we haven´t learned how to correctly design our landscapes. Through keeping our land covered with organic material, and building swales and ponds, we can increase the resiliency of our landscapes through aiding in the storage of rainwater in the landscape.