Remembering rain.

• Author: Payne, Troy L.
• Position: Rainwater harvesting techniques

1. INTRODUCTION II. WHAT IS RAINWATER HARVESTING? A. Microcatchments B. Rooftop Harvesting C. Artificial Recharge III. THE ILLUSION OF SCARCITY AND THE MYTH OF ABUNDANCE A. India: The Illusion of Scarcity--Toward Jal Swaraj 1. The Past: Fertile Deserts 2. Wisdom Survives: From Dark to White 3. The Struggle: Community Versus Government B. United States: The Myth of Abundance--After We Have Dammed All the Rivers 1. The Past: America's Ancient Southwest 2. Wisdom Survives: Scattered Memory and Fractured Response IV. RECOMMENDATIONS, LARGE AND SMALL A. Education B. Government Support for Rainwater Harversting I. INTRODUCTION

   A leaf stretches out and catches a drop of rain, channeling water toward the ground at its base; for millions of years, this simple rain collection technique has fueled life in many reaches of this planet. A few quiet moments in the rain are all we need to remind us of how plants catch and drink the rain. Yet, raised in a society where the government provides and regulates all the water we use, luxury has outpaced ancestral understanding. Perhaps in only the last few centuries, we have forgotten how to collect the rain, ignoring techniques developed over millennia by diverse civilizations to provide water to drink and irrigate crops. In the most arid regions of the planet, stretching across the modern Middle East, Africa, the Asian subcontinent, and the American southwest, our ancestors learned to turn as little as one-half foot of rain per year into enough water to drive flourishing cultures. Today, in the face of modern engineering of dams and wells and massive irrigation systems, water shortages in these regions fuel famine, disease, poverty, and conflict, though no less rain falls. Something is missing ... and it is right over our heads.

   Modern cultures predominantly draw on surface and ground waters to fill their water needs. As centralized control characterized by bureaucratic governments took control of water, the individual's responsibility for her own water declined. Traditional designs for providing moderate amounts of water have given way to large-scale public projects designed for total physical development and control of lakes, rivers, and aquifers. These methods have been insufficient to meet the needs of the poor in most parts of the world, and overextraction has put innumerable ecosystems at risk in those places where water development has fueled economic prosperity. All the while, rainfall sweeps across deforested lands, eroding topsoil and dumping silt into our rivers and streams. Runoff rages through concrete cities from rooftops and roads. Unable to seep into the ground to recharge aquifers and support rivers, it carries pollutants and toxins into the waterways. Population growth in many countries has simply outpaced the current technology's capacity to provide water sustainably. Rivers are drying up. Water tables are falling. Regions that once supported forest ecosystems are barren, and people are abandoning them as inhospitable. Clean water is wasted by some as if it were a right to water a garden with Evian ("naive" spelled backwards). This is not hyperbole--these are stories about forgetting rain. We should all take notice long before we have to depend on government water trucks to deliver a sip of water to our door. We must move ahead to the past.

   Memory has proven resilient. Across the globe, rainwater harvesting techniques are reappearing in a variety of individual, community, and government projects. The solution to many of the world's water needs may well lie in the ability to manage and utilize rainfall and runoff. We can capture rainwater in barrels to water our houseplants. We can corral runoff or floodwaters with catchments to recharge groundwater for drinking or irrigation. We can revegetate deserts and bring back rivers, and we can do this while we reduce pollution and erosion and poverty and hunger. This effort is both as simple and as complex as the leaf of a plant. What it takes is a broad surface to collect the rain, guidance to a place to collect it, and the will to make it a part of our daffy lives. We have the broad surfaces: a roof or the ground, for example. We can build the infrastructure: gutters and pipes, pumps and storage tanks, check dams and ponds. Most important, we need the will to make rainwater harvesting a part of our lives, by educating people to be responsible for their own water, fostering the political will necessary to remove legal barriers to rainwater harvesting, and developing cooperation between individuals, communities, and governments. Just as it is important for the Earth's hydrologic cycle, rainwater harvesting should be a part of the human strategy for water management.

   The purpose of this Article is not to catalog every effort across the globe at reviving rainwater harvesting. We wish to demonstrate by a few examples that rainwater harvesting has had an important role in water management in our past and should have a similar role in our future.

   Part II briefly outlines a very basic definition of rainwater harvesting through a description of the most common technologies for capturing the rain and putting it to use. Part III explores the ancient and modern uses of rainwater harvesting techniques in two very different places: India and the United States. This comparison demonstrates the broad utility and capacity of rainwater harvesting and the institutional barriers impeding water self-reliance. Finally, Part IV offers some suggestions for how rainwater harvesting can be encouraged as an effective means for meeting long-term water needs.

2. WHAT IS RAINWATER HARVESTING?

   Rainwater harvesting requires two basic elements: a catchment--a broad surface to catch the rain--and a method or device for storing the captured rain. (1) The catchment may be as simple as furrows in the ground or the roof of a building--the size, depth, and shape dictated by the region's topography, amount of rainfall, and the proposed use of the water. (2) The rainwater can then be stored in a variety of ways: in the soil to nourish plants, in cisterns or tanks for livestock and domestic purposes, or in ponds to water crops or to recharge groundwater. (3)

   Traditional methods for capturing rain for crop irrigation, drinking water, and aquifer recharge developed over millennia across diverse cultures and regions of the globe. (4) These methods supported civilizations in arid regions that otherwise would not have allowed for agricultural production due to the lack of precipitation or the frequency of drought. (5) The names of and techniques for the capture and use of rainwater are as varied as the cultures and landscapes from which they developed. Further, elements such as rainfall amounts, volume of rainwater collected per area of catchment, runoff rates for rock, soils, or metals, and the volume or quality of water required to support plants, livestock, or humans are all design decisions particular to specific sites. However, a description of three basic methods, capable of employment in some form in almost any dry region of the world, (6) will serve as an adequate foundation for this discussion.

   1. Microcatchments

      A microcatchment is typically an area of ground dug out and supported by earthen walls (serving as "check-dams") to capture rainfall directly or to harness runoff from hillsides or floodwaters along the banks of rivers during periods of heavy rainfall. (7) This technique takes advantage of rainwater that evaporates too quickly to seep into the water table or to sustain plants as it moves over hot, dry land, or that would otherwise carry silt and surface pollutants away to streams and lakes. Microcatchments are usually employed in rural areas for watering livestock and crops and to aid in water retention to maintain water table depths. (8)

      The simplest technique is to create microcatchments in low-lying areas or along moderate slopes. There are a variety of shapes employed depending on the landscape: diamonds in forested areas, contours or strips along slopes, and semi-circles along riverbanks. (9) These elements can be constructed and reinforced using very basic technology.

      The amount of rainfall, the volume of water needed, and the area available for catchment purposes will determine the size of the catchment, which may range from small-scale "micro"-catchments to larger, more complex "macro"-catchments, hundreds of square meters in size. (10) Counter intuitively, the smaller the catchment structure, the more water it retains. For example, in dry regions, ten one-hectare catchments will yield more water than one ten-hectare catchment. (11) In the larger catchment, the water travels over more ground to reach the dam, thus is lost at a much higher rate to evaporation and to shallow seepage; the greater surface area of the larger catchment also increases losses to evaporation. (12) Therefore, smaller structures are more efficient and are well-suited for rural, community projects. (13)

      These structures, as they often hold large volumes of water, must be well-maintained to ensure that the check-dams will not give way or be overcome by heavy rain or flood that could completely destroy the structure. (14) For this reason, larger catchments may require the knowledge and support of engineers for construction and maintenance. Also, catchments need to be inspected for weeds and insects that might cause structural damage. (15)

   2. Rooftop Harvesting

      Just as the ground may be used as an area to capture rainwater runoff, so too may rooftops, which provide a large and readily available catchment surface in both rural and urban settings. The basic rooftop harvesting system requires a roof of suitable material, as well as gutters or pipes to transport the collected water to a storage tank. (16) The roof must be made of a nonporous material, such as non-corrosive metals, plastic, or tile, to facilitate runoff and avoid adversely affecting water...