How to catch rainwater where it falls - An intoduction

A manual -for anyone who wants to make good use of rainwater wherever it falls in the landscape.

 Perhaps you are a farmer and you want to practice good water and soil management for your crops and trees, or you own some land and you want to manage it carefully to recharge the groundwater. You may be focusing on what you can do with your own land, or wondering what your community can do, or you may even be thinking at the watershed level. This manual will suggest a number of helpful techniques. Ideally, these techniques should be applied with the cooperation of many people across the whole watershed, but you can also begin with your own land. Many of these ideas are still being developed and tested, so you can help to improve these methods by trying them out and keeping track of the results.

If you want to grow crops on your land, you should consider both structural measures and agronomic measures for water harvesting and conservation. Structural measures, discussed further below, involve building structures for rainwater harvesting using materials such as soil, stone, wood, cement, etc. But the details of how you farm your land (agronomic measures) are also very important for water conservation. Pitcher irrigation is another helpful agricultural technique.

What if the land is highly degraded, making agriculture difficult or impossible? For example: the topsoil has eroded away, the soil is thin and compacted, the land is stony, and there is almost no natural vegetation. See pitcher irrigation for a summary of techniques for restoring vegetative cover in degraded lands. Restoring vegetative cover will help prevent further erosion and will also reduce runoff.

One of the simplest structural methods for slowing the movement of water and soil over sloping lands is the use of bunds, which are small raised ridges across farmland – less than 1m wide by 1m high. Bunds are usually built following the contours of the landscape. When land is steeply sloping, there are several additional techniques that will be helpful.

If there are small gullies in the landscape, it is important to do something to prevent further erosion (techniques for steeply sloping land). Such techniques can also increase moisture retention. The techniques will vary depending on the size of the gully. For larger gullies or valleys, the main goal of building check dams may be to facilitate water infiltration and retain silt for planting, or to create a tank for irrigation.

On sloping lands or less permeable soils it may be helpful to build groundwater recharge structures that facilitate percolation of rainwater into underground aquifers for storage (groundwater recharge structures). Underground storage is most efficient because evaporation losses are minimized. In other situations, it may be desirable to make a farm pond and store water on the surface.

Ideally, all of these methods should be thoughtfully applied throughout the (watershed). Such application will require cooperation and teamwork. Certain techniques and agricultural practices are better for upland areas, while other techniques and practices are better for lowland areas. The costs of water conservation measures and the returns from water harvesting should be shared between landowners in upland and lowland areas.

Water harvesting projects will cost some money in the beginning—cost of labor for digging, seeds for planting, materials, etc. However, many organizations have found that the projects pay off in the long run, especially when they involve planting trees and fodder which will be productive over time. It is helpful to keep track of expenses and returns by year in order to see how it works out. Loans should be made available to farmers / landowners interested in beginning such projects to help cover the initial expenses until the project begins to yield profits.

Before starting any project, it is helpful to take a closer look at your landscape:

What is the slope of the land? You can make simple devices for measuring slope and marking contours.

  • What kind of soil are you working with? Is it red soil, or black soil? Is the soil highly erodable? Well drained? Poorly drained?
  • How deep is the soil? This will influence what type of structures you can make. You can dig your own pit to find out, or you could also talk with other people nearby who have been digging—whether for wells or construction projects.
  • How deep is the water table? Again, people who have wells will know. The water table will vary throughout the year. If the ground becomes waterlogged at some point during the year, the water table may actually come up to the surface.
  • What is the annual rainfall, and when does it fall during the year?
  • What materials are readily available for building? Soil, rocks, wood, brush?
  • Are there gullies in the landscape? A gully is a place where water is carrying away the soil and has created a channel at least 1 meter deep. Gullies will naturally deepen over time, unless you do something to stop the erosion. Gullies are also a good place to create a structure for catching rainwater.
  • Where is the water in the landscape? Are there any places that stay wet throughout the year? Ponds, marshes, streams? What about streams that only flow for part of the year? What about streams that only flow after a big rain?
  • What are your water needs? Are you looking for a source of irrigation water during times of drought? Do you need to store water on the surface, or can you store it underground and draw it up from a well?
  • What is the water infiltration rate? At different depths? You can compare infiltration rates using a small length of pipe and a watch. (measuring water percolation rate)
  • It is always necessary to balance the needs of humans and other living creatures. Take a look at the vegetation that naturally exists in the landscape. Try to maintain that vegetation where possible. Are there places where birds and land animals come to use the water? Are there fish in the local water bodies? Look at what is there before altering the landscape, and avoid damaging places with diverse and abundant plants and wildlife.

The following pages go into more detail on the techniques mentioned above.

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