Article: Flood Prevention with Permaculture

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flood prevention with permaculture(or, what we might have done with hindsight)
by cathy holt

Are severe floods, mudslides, contamination of rivers, and loss of property such as we’ve just experienced in Western North Carolina unavoidable?

With intelligent design, can we prevent the damage caused by flooding—both to ourselves, and to the life-giving streams and rivers that flow through our area? How can we come closer to replicating the natural hydrological cycle?

Permaculture is “the practice of creating mutually beneficial relationships with the natural world.” (Penny Livingston) A set of design principles to help humans live more harmoniously with nature, Permaculture helps us make better use of resources by observing how nature does things. It’s also been defined as a way of maximizing the yields of the landscape to meet the needs of its inhabitants.

Here are a few ideas from Permaculture that can help turn the problems of flooding into solutions, both for individuals and municipalities. Bill Mollison, one of the founders of Permaculture, likes to say, “Where the water runs, make it walk.” Each of the following is a way to slow that flow.

1) Dig swales. If you have property with a fairly steep slope, dig swales (trenches on the contour line) high on the hill, and plant trees or shrubs in them. This is, of course, a good practice on public lands as well. Swales catch and hold water, allowing precipitation to soak in rather than run downhill, causing erosion and flooding. Earth dug out of the swale is piled up on the down-slope side, providing a barrier for the water known as a “berm.” Soil’s ability to hold water can be increased by 70 to 85% by swales, berms, and vegetation. Thus, groundwater can be recharged.

2) Diversion drains can be dug to help channel precipitation away from roads and creeks, and into swales or level areas. They keep water from flowing straight down a hill, thus slowing it and allowing it to soak in and spread out over a larger area; they also help keep contaminants from entering streams.

3) Plant trees to help slow down or prevent runoff. A Douglas fir can capture as much as 43% of the annual rainfall! Trees have a large surface area of leaves which catch water and drip it more slowly to the ground; their roots hold water and topsoil; the mulch of leaves, especially in a forest, is like a sponge. Trees thus help to recharge groundwater. Primeval forest has NO runoff, while farmland has 25% runoff, and urban paved roads, parking lots, sidewalks, and roofs have 100% runoff. Moreover, a tree is like a standing column of water; it is 86% water. Trees absorb large quantities of water and evaporate it slowly back into the atmosphere. Logged areas hold less water; soils erode and cause silting in streams. It’s a good argument against logging in any watershed areas, especially those draining into our drinking water.

4) Collect your roof water in a rain-barrel or cistern. This keeps some water from entering the storm sewer system. The major cause of raw sewage entering rivers is that most sewers are not designed to handle a large amount of storm water in a short time. A 1000 square foot roof will collect 625 gallons per inch of rainfall! With good filtration and a non-toxic roof, you can even drink the rainwater you collect. It can be alkalinized with limestone and oyster shells. There is a simple device called a “standpipe” that allows the first wash of water from the roof to be diverted away from your storage barrel or cistern, and discarded. Besides valuable drinking water (which many, many people lacked after the floods), the rain water can be used for anything from flushing your toilet to showers to laundry to watering your garden. Although it’s easier to plumb a new house for such purposes, some existing homes can be retrofitted.

Most folks don’t think of water conservation during a flood, yet the irony is that floods frequently cause a cut-off of safe water for drinking and other household uses. We might also remember that global climate change, due to the high emissions of CO2 and other greenhouse gases in our industrialized and automobile-dependent society, can cause droughts as well as floods and hurricanes.

5) Decrease impervious surfaces. “Increased frequency and intensity of flooding is directly correlated to increased area of impervious surface in the drainage basin.” (“Urban Stormwater Management,” The Permaculture Activist, May, 2002.)


Impervious surfaces cause extreme fluctuations in water volume and flow, leading to erosion of stream beds and banks. Water quality degradation is also related to the amount of paved area in the watershed, which allows pollution to be washed off roads into storm drains and piped to the nearest stream. Paved areas can be replaced with “absorption beds”—gravel, or cinder blocks with open spaces, or bricks with spaces in between. Absorption beds are an especially good idea for areas where vehicles are parked, since this allows any oil drips and other pollutants to sink into your local ground instead of being carried down into the storm drains and thence into the creeks. Diversion drains (see above) can carry water away from paved areas such as roads, and divert it from flowing down into storm drains.

A living roof is a beautiful, green alternative to the impervious rooftop, and some rainwater can still be collected from it. In Europe, the green roof is covered with grasses or groundcover. Benefits include: controlling stormwater peak flows, reducing volume of runoff, improving stormwater quality, providing wildlife habitat, reducing urban “heat island” effect, improving insulation, producing oxygen and storing carbon. German studies show that up to 75% of the rain that falls on a green roof is absorbed, and slowly evaporates off. A huge factory, Ecover in Belgium, has a roof with 2 acres of native grasses and other vegetation. Stormwater is collected and used for toilets.
In Maryland, a residential subdivision has adopted “Rain Gardens” as a stormwater management technique. Each 10,000 square foot lot has a 300-400 square foot rain garden, designed so that rainwater forms a small pool which then evaporates or soaks in within 2 days. These rain gardens are planted with vegetation that tolerates both wet and dry conditions, and absorbs the pollutants captured. Along with roads that drain into roadside swales, this project diverts considerable storm water from traditional storm sewers.

6) Gabion that gully! Where erosion pathways are already established, a simple “gabion” (a collection of rocks stacked up to 3 feet in height, held in a wire basket), placed fairly high on the slope, can slow down and spread out the water and its erosive force, while causing soil and silt to be retained behind the gabion. Over time, a series of gabions will “harvest” both water and soil, creating a very fertile, stable, and well irrigated bed of soil in what was previously a deepening gully or arroyo. A gabion can be built of rocks, brick, old chunks of concrete. These simple structures can prevent roads from washing out, and retain topsoil while protecting creeks and rivers from sedimentation. For a fascinating description, see “Where Rocks Have Made the Water Flow,” The Permaculture Activist, May 2002.

7) Create parklands. On an urban planning level, there is much that can be done. It is wise to remember that periodic flooding is inevitable (and we’ll have more severe storms as global climate change proceeds) and to plan for it. In fact, periodic floods can be healthy for natural river systems. No toxics such as home heating oil should be stored in a floodplain, nor should businesses or homes be located in it.
The visionary mayor of Curitiba, Brazil established green zones and parks in all the river floodplains. Besides being wonderful for wildlife, these parks became one of the city’s major attractions to both residents and visitors, and prevented businesses and homes from being flooded. When these parklands have riparian buffer zones with plenty of trees and shrubs, flooding is much less of a problem, and fish are more likely to flourish in the streams. The vegetation can help filter storm water that runs off the roads toward the streams. For example, one mature tree can filter up to 200 pounds of nitrates , a common pollutant from chemical fertilizer, livestock and/or human sewage, per year. Ponds can also be created, to hold rainwater and provide habitat for a wider diversity of wildlife. “Retention ponds” allow silt to settle out before water from the ponds enters a stream or river.
Resources:
This article relied heavily on information in The Permaculture Activist; see permacultureactivist.net.

For information about rainwater storage systems, see blueridgeatlantic.com. To view some simple, low-cost or do-it-yourself rainwater storage systems, visit Earthaven Ecovillage (earthaven.org). You can also learn about graywater treatment systems and composting toilets there. Tours are available every Saturday morning at 10:30 AM, by appointment; call 828-669-3937.

Cathy Holt is a permaculture teacher, holistic health practitioner, and author of The Circle of Healing: Deepening Our Connections with Self, Others, and Nature. She is currently working with the Asheville Kindness Campaign and can be reached at 828-252-3054.


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