Four not-very-sexy initials are reinventing the design and resource management professions in the United States 28 years after the adoption of the Clean Water Act. TMDL (total maximum daily load), an abstruse acronym for a concept lacking a catchy nickname, has been shoved onstage to do the water-quality thing by twin cousins with equally awkward names: point- and nonpoint-source pollution. Together, this trio is revolutionizing the water-quality world, changing the way we use natural resources, and putting landscape architecture, civil engineering, transportation, and land-use planning in the limelight of “green design.” And erosion control is right in there playing a major role.

In short, states are beginning to prescribe TMDLs of specific pollutants for water bodies that do not meet state or federal water-quality standards. This is putting business-as-usual in the back seat. At the wheel and making money are enterprises and industries that have learned to incorporate water-quality protection into their everyday designs, facility programs, and project maintenance and operations. And their government clients are sitting close beside them, loving every word they hear because they are under pressure to produce improved water quality.

It Starts With Runoff

As anyone who has left the hose on too long knows, an intense or long storm can send runoff trickling into every little dip in the landscape, where tiny rivulets form and eventually find their way to gutters, storm drains, or creeks. If the soil is bare, compacted, or already saturated, or if dashing water clogs soil pores—limiting infiltration—runoff can be rapid and copious, generating a slug of sediments and swilling it into the nearby gutter, ditch, or stream. But if the sprinkler is set low and the soil surface is protected by plants and organic material, the water will seep into the soil, recharging groundwater resources and, ultimately, feeding rivers and streams.

We know that whether runoff events are rapid and dramatic or slow and imperceptible, the materials stormwater comes into contact with are potential sources of water pollution. An acquaintance whose job it is to translate agency science into sound bites for laymen puts it this way: Because of rainfall, runoff, and recharge, anything that gets left outside eventually ends up in a river.

Solutions Address Land Use at Sources

But determining whether the sources of water pollution are point or nonpoint can be troublesome when runoff and erosion are involved. Pollutants that commonly adhere to sediments—such as zinc, copper, lead, total phosphorus, PCBs, DDT, and some insecticides—may be picked up by stormwater runoff, and hence their source might be considered nonpoint. But if they run off into a stormwater system and are discharged to a water body by a pipe, the source may be considered a point source. We might be tempted to say, “What’s the difference?” when the result is impaired water quality.

The difference can play out at the local level in whether we choose to treat the runoff or treat the land use generating the pollution. These are complex decisions that get into issues of property rights, the muscle and fiscal strength of local government, the political will of locals and their willingness to pay for water quality, and the regulatory culture of state government. Section 303(d) of the Water Quality Act, which requires statewide identification of water bodies that don’t meet federal water-quality standards, has opened Pandora’s box of local responses to TMDLs for quality-impaired water bodies. These prescriptions put quantitative ceilings on the allowable daily loads of specific pollutants for specific water bodies but do not tell local government how to achieve the desired results. What will be done also will depend on the pollutant, the water body, and the beneficial uses it supports.

If we look at a list of generic nonpoint sources of pollution, we see a reasonably concise inventory of land uses and activities: agriculture, construction, mining, forestry, urban stormwater runoff, marinas and boating, sewage treatment plants, and various modifications to hydrologic systems, such as ditches. But if we look at EPA’s list of water-quality criteria and standards, we see a mind-boggling array of chemicals and compounds most of us hoped we’d left behind forever after we somehow managed to pass our required chemistry courses. Each of these can be associated with specific sources, activities, or land uses. Many are being addressed through EPA’s National Pollutant Discharge Elimination System (NPDES) permit program for industrial and commercial discharges. Others are falling under the TMDL orders administered by states. Still others, as we shall see, may be slipping through the regulatory net.

Here’s How It Works

To each water-quality parameter on EPA’s list are attached minimum standards of concentration for acute and chronic toxicity for human consumption and other beneficial uses of water. Designated beneficial uses are an important part of TMDLs, and we’ll get back to this in a minute. If a water body does not meet the criteria necessary to support its beneficial uses, a TMDL may be prescribed. Local government then figures out how to bring the pollutant levels down to federal and state standards by curbing the pollution source or sources.

Of interest to the EC professions is that total suspended solids (TSS) are on EPA’s list of water-quality criteria and standards but are rated as neither carcinogens or priority pollutants, nor as chronically or acutely toxic in marine or freshwater systems. The states have set various standards for TSS, but many have had difficulties enforcing them because of the intricacies of establishing background levels or determining impacts of TSS on some beneficial uses. All of this demands rigorous monitoring. These ambiguities forewarn of complexities to come as the role of nonpoint-source erosion continues to be scrutinized in the field of water-quality protection. Of particular interest is the role of sediments derived from human activities in affecting the quality of aquatic habitat for endangered species—an acknowledged beneficial use.

Beneficial Uses Are Key

We know that state and local governments classify water bodies according to the beneficial uses they support: drinking water, swimming and other water-contact recreation, noncontact water recreation, irrigation, industrial and commercial uses, and preservation of aquatic or riparian ecosystems. In regions where threatened and endangered aquatic and riparian biota have become pressing concerns for all levels of government, there is growing attention to the water-quality parameters that support the systems: dissolved oxygen, temperature, pH, turbidity, suspended sediments, algae, aquatic weeds, nutrients, channel form, and streamflow characteristics. When aquatic ecosystems are considered a beneficial use, the role of TSS in affecting them gains stature.

This fact is causing natural resource managers to reinvent the way forestry and agriculture are practiced, how roads are located and constructed, and how watersheds are managed. Meanwhile the design professions are changing the way cities are built, drained, and maintained. We in the ESC professions might be tempted to think our local erosion control ordinance is taking care of the sediment piece of this big water-quality picture. But there are limitless opportunities for ESC professionals to provide input on both policy- and project-level decisions about point and nonpoint erosion on both watershed and project scales. This is because a great deal of accomplishing TMDL goals for water-quality-impaired waterways turns out to be about controlling nonpoint runoff and the pollutants associated with it.

In the simplest terms, these controls are about limiting runoff quantity, controlling the substances stormwater touches, and providing some kind of treatment of stormwater before it seeps into the ground or discharges into streams. In the most complex terms, controls are about the standards we apply to development and natural resource use and the mechanisms we use to fund, enforce, and monitor the effectiveness of such measures.

Runoff and Erosion Play Subtle Roles

Let’s take, for example, a watershed in which there is forestry in the headwater zone, agriculture in the midslopes and major floodplains, and urban uses elsewhere. Even if sediments are not a factor in a TMDL for the stream, erosion of disturbed soils can play an essential role in other parameters of the TMDL.

In the timber-production zone, higher-than-background sediment production can be generated in several ways. Drainage of nonsurfaced roads may be one; logging disturbances in the riparian zone may be another. In some cases, clear-cutting and/or broadcast burning may be responsible for delivering sediments to streams. If streams in the timber-production zone are getting a big slug of sediments, these sediments may be transported downstream long distances until gradients become low enough that the sediments will settle out. In stream zones where accelerated aggradation is taking place, the channel may become wider and shallower. As this occurs, stream temperatures might rise, exceeding federal or state criteria. Although loss of stream shading or a disturbance in flow regime may contribute to a temperature problem, erosion control may be an important factor as well.

The same thing holds true for agriculture. If aggradation from eroding farm fields is affecting channel morphology and instream habitat for endangered aquatic species, the land uses generating the sediments might need to be scrutinized and tweaked.

Similarly, erosion may be identified as contributing to a turbidity problem even if suspended sediments are not a factor. Water-quality monitoring may identify an abundance of phosphorus, a nutrient naturally occurring in local soils. Erosion of these soils may be increasing phosphorus levels in area streams, which support short-lived blooms of algae. As the algae increase, their nighttime respiration can deplete dissolved oxygen in the stream. Low dissolved oxygen and a high variation in pH caused by these blooms can have direct and indirect effects on stream life. Again, project- and landscape-level erosion control may have positive impacts on turbidity levels, even if sediments are not a factor in the TMDL.

In the urbanized area of the watershed, nonpoint erosion may provide the vehicle by which diverse and dispersed pollutants enter stormwater systems and, hence, streams. One example is runoff and erosion of landscaped areas, where insecticides may be applied as preventatives, fertilizers applied for aesthetics and to help primary vegetation compete successfully with weeds, and herbicides applied to keep the ground free of vegetation for safety, sight distance, or other purposes. The effects on water-quality of nonpoint erosion from these and other urban land uses can be extremely complex. While some of the potential impacts of such erosion from industrial and commercial land uses are regulated by the NPDES stormwater permits, nonpoint pollution stemming from unregulated land uses might slip through the net but could be an important factor in local water-quality impairment.

BMPs Are the Basic Tools

Land-use control, as we often hear at the local level, is not the business of state or federal government. But local sentiments about property rights may result in municipal government not being able to effectively restrict polluting land uses. Or local government might not have the fiscal resources or political support to apply restrictive zoning or development standards that can protect local water resources. In an interesting way, private enterprise has stepped in to close the gap with the help of EPA and an armload of handbooks on BMPs for nonpoint-source pollution control. The agency has developed a slew of BMPs for protecting water quality from the impacts of a range of activities and land uses. These give locals a menu of choices and some flexibility in meeting state and federal water-quality targets.

Companies that have been paying attention have snatched up these handbooks as they roll off EPA’s presses and parlayed them into big business for hungry government clients who are striving to meet TMDLs. They have inserted best management practices (BMPs) into designs for transportation and utility projects, wetlands protection and mitigation, urban redevelopment, construction in environmentally sensitive areas, and a host of demonstration water-quality projects in the watersheds of 303(d) streams.

Meanwhile, local governments with sufficient political cachet have modeled elaborate stormwater codes and rules on the findings of EPA’s and others’ water-quality research and, in doing so, have created booming local “response” industries in environmental engineering. The prevalence of 303(d) streams, TMDLs, NPDES stormwater permits, Section 404 (wetlands) projects, watershed management, and endangered species listings has boosted the field of erosion control into this growing industry of water-quality protection. Erosion considerations now have a seat at the table in watershed-scale natural resource management and have become important in the design, construction, operation, and maintenance of a raft of increasingly complex projects.

Tools Get More Complex

And the tools of the trade are becoming more complex. Positions for urban water-quality specialists and TMDL managers are beginning to appear in municipal government and agencies. The people coming into these positions are trained in soils and erosion, chemistry, industry, and stormwater, and they have the ability to crank and tweak complex equations with sensitive factors. Increasingly, these specialists are being asked to assess the efficacy of specific BMPs for specific land uses of specific areal extent on specific soils and slopes in specific climatic zones on specific drainage routes to receiving waters with specific pollutant loads. They use references such as EPA’s draft tutorial for water-quality specialists, which is peppered with matrices of factors to plug into equations for calculating pollutant loads, concentrations, and receiving water impacts. They refer to tables that list the most frequently detected priority pollutants, their most common sources by land use, and the most efficient removal mechanisms for each pollutant type.

Of course, it all comes down to site design and programming, management of stormwater and stream corridors, and good old BMPs. EPA classes BMPs in four broad categories: storage, infiltration, filtration, and vegetative practices.

Natural landscaping, a growing family of vegetative BMPs, is getting a lot of attention because of its potential to meet multiple objectives in water-quality improvement. Hot off the press is EPA’s new Source Book on Natural Landscaping for Public Officials ( The publication of this manual speaks volumes about the shift in focus that local governments increasingly will be making in response to state-prescribed TMDLs on local water bodies. In this case, the shift may be in design standards for landscaping in the watersheds of certain TMDL streams.

Design Shifts Will Result

Big business is lining up to meet these changing objectives with teams of biologists, landscape architects, botanists, engineers, and water-quality specialists. Tomorrow’s industrial site or office campus may be a TMDL landscape, well conceived and executed to provide infiltration opportunities that minimize runoff and its deleterious impact on urban hydrology. Such landscapes will also filter sediments and provide vegetative uptake of stormwater pollutants. Their shade will protect runoff and streams against thermal pollution. Native plants in these landscapes will cut down on the need for fertilizers, pesticides, herbicides, and maintenance and will provide habitat for wildlife. These multifunctional landscapes will provide connectivity with linear greenspaces that protect floodplains and riparian corridors while supplying areas for utilities, passive recreation, and wildlife movements.

Paradigm shifts such as these for landscape design increasingly will come about in order to meet TMDL requirements. These requirements are throwing enormous challenges to natural resource managers, municipal governments, and the design professions. One of the largest challenges will be figuring out how to spread the burden of pollution control to nonpoint-source producers. The control of nonpoint erosion in agriculture, timber production, public greenspaces, and urban settings will play an important role in meeting TMDL goals. This challenge will create equally enormous opportunities for erosion professionals to contribute fresh solutions to land use and stormwater management.
About the Author

Martha S. Mitchell

Martha S. Mitchell, CPESC, is principal of ClearWater West Inc. (, consultants in erosion and natural resource planning in Portland, OR.