The clearing of land across the landscape for farms and ranches, combined with the constant development of commercial and residential areas, has led to widespread problems of flooding and reduced groundwater recharge.

Water runoff is predictably accelerated by human activity. With the clearing of natural vegetation comes the addition of impermeable surfaces (roofs, roads, concrete, and other "hard" surfaces). Without the landscape's natural surface, water can no longer soak into the soil; accelerated stream flow, flooding and erosion results.

Integrated Community Design
To achieve the needed balance of natural surfaces within developed areas, designing high density housing is one strategy that leaves a large portion of natural area intact. Open spaces, designed as urban forests or park lands, can be integrated throughout a community and can be successfully designed to mitigate stormwater in an attractive and biologically functional manner.

Few strategies offer better response to minimizing flood damage than appropriate placement of communities in relationship to the total landscape. Appropriate placement first requires a comprehensive understanding of the entire landscape ecology. By learning to "read" the landscape, all community land use planning and design can work comfortably and economically with  (not expensively against ) the landscape's natural processes and topography.

Landscape Dynamics & The Hydrologic Cycle
In order for a community's stormwater action plan to effectively and efficiently address flooding, the action must consider and compensate for the constant subtle changes that occur in the "landscape dynamic." The action plan must also have an enhancing effect on the hydrologic cycle.

The hydrologic cycle includes not only water; but air, vegetation, and the soil of the landscape. Water continuously cycles through the environment as rain, streams, and vegetation.  Through evapo-transpiration, it cycles back to rain. This action of the water cycle, together with the landscape dynamic, works to enhance vegetation, increase air humidity and saturate groundwater.

The amount of runoff that occurs is due to various physical features. Density of vegetation, slope, conditions and composition of the soil as well as the intensity and duration of a given storm event will all have an affect. In areas with dense vegetation the soil absorbs rainfall quickly and in most cases entirely. Forested areas typically have less than 10% runoff. Urban areas (with mostly hard surfaces) and some arid regions of the world (with sparse vegetation) have up to 80% runoff or more.

Runoff moves through the whole landscape profile in several predictable flow patterns. Water moves first as rainfall, then moves laterally as overland flow or "sheetflow." Sheetflow then creates very small channels which eventually join together forming small streams. Small streams join together forming larger streams which join together to form rivers.

Water can also soak into (infiltrate) the soil. The water that moves laterally (to a stream channel) under the surface is called "interflow." Interflow can also be drawn down to create an area where the soil is completely saturated called "groundwater." The volume of stream flow is increased when the groundwater is saturated enough (recharged) to rise and meet the level of the stream or when the downcutting action of the stream cuts into the groundwater area. This contribution, from the groundwater source to the stream, is called "base flow."

Mitigation Trends
Technological approaches to stormwater mitigation have not always solved flood problems. In many areas approaches such as detention basins, culverts and stormwater drains have high maintenance costs and problematic results.

Detention basins, designed to control peak water flow, only delay it temporarily. Water may be "control released", but often the released water is combined with that of nearby tributaries causing extensive flooding over an even longer period of time (than would have occurred without detention). Released detention water moves quickly over the surface and doesn't soak into the soil. Without infiltrating, this water cannot contribute to groundwater quality nor recharge base flow.

Culverts, in almost every instance, accelerate the velocity of water flow which causes erosion. When not properly maintained culverts are easily clogged by accumulated silt and debris, causing further outflooding and washouts.

Stormwater drainage systems require extensive engineering, and function solely to remove water from the landscape - making this valuable resource completely unavailable for use. As water washes from roads and through industrial areas, storm drains pick up and carry away concentrated pollutants. These pollutants are then discharged directly into water courses. This discharge is often at high velocity which also accelerates erosion, especially at the point of discharge.

Biological Mitigation
Biological approaches use "low-tech" (and often low cost) strategies that work in harmony with the natural landscape. One of the most successful mitigation strategies employed in dryland ecologies around the world is to "harvest" water for infiltration. When infiltration strategies are implemented, downstream flooding is reduced and groundwater is recharged.

Infiltration works by intercepting overland flow, before it has a chance to cause any downstream flood damage. Water is held, by berms and basins, until it percolates into the soil strata. Stream flow returns as a result of saturation and high contribution to base flow (not because of accelerated overland flow).

The frequency, volume and shape of infiltration basins can be designed to accommodate a variety of desired effects and actions. Basins can be designed so that they do not create undesirable conditions of mud or provide habitat for mosquitoes. Infiltration action can also be used to increase water quality. As water percolates through the soil, metals and other pollutants are diluted and filtered out (partially or completely) by soil organisms before the pollutants reach the groundwater area.

Shallow, broad-based basins, called "swales," constructed along the natural contour of the landscape are effective means of capturing overland flow for infiltration. In the 1930's, conservation crews constructed infiltration swales all over the southwest. Swales catch run off water, facilitate a high growth rate for vegetation and closely mimic a normal stormwater return rate into the soil as it would have been before any development occurred.

A successful infiltration program would require broad-scale implementation, in most communities, this would require a cooperative regional management plan. Infiltration strategies are best employed as high as possible in a watershed profile. High in the uplands the soil is well drained, the channels small, and the volumes of water that can be expected are the most manageable. Downstream flooding is reduced (or eliminated) and the whole watershed benefits from recharge.

Community "EcoNomic" Development
The opportunity exists for further integrating water harvesting with economic development. A best use of recaptured water resources would be in community-wide planting programs of useful trees, shrubs, vines and grasses. Some of the water harvesting structures (contour swales) can serve double duty as pedestrian and bicycle paths. Commercial orchards, retail nurseries and market gardens can be developed and integrated as vocational training programs, environmental restoration, and other community service programs.

Converting Problems Into Resources
Designing in balance with the natural patterns of the landscape effectively converts flood problems into multi-purpose community resources. An ecological approach to stormwater mitigation may require intensive, multi-agency planning efforts, but in the long run, would provide a highly improved quality of life and most importantly, it would offer hope for an economically and environmentally sound future.

Larry Santoyo is a Land Use Planner and Environmental Business Consultant. He is among the most experienced Permaculture Design Instructors in the US and has over twenty years experience in resource protection and natural systems management. He can be contacted through his website at Earth Flow Designs.

This article was reproduced here with his permission.