Watershed Protection and Management

Module 1: Introduction to Watersheds

Topics

I. What Is a Watershed?

II. Stream Order

III. Watershed Regulations

IV. An Introduction to the Remaining Modules

I. What Is a Watershed?

The term  watershed  refers to an area of land that drains water to a particular point along a stream, river, or other water body. Topography and surface runoff are the key elements affecting this area of land. The boundary of a watershed is defined by the highest elevations surrounding the water body. Think of a watershed as being like a sink. The interior boundary of the sink represents the watershed, and the sink's drain is the point at which all the water drains. A drop of water falling outside of the sink, or boundary, will drain to another watershed. Figure 1.1 provides an example of how a watershed's boundaries are delineated.

Figure 1.1 A Sample Watershed Delineation of Sadie Run

Source: Center for Watershed Protection (2006); used with permission

Drainage Areas

A watershed's drainage area is a measurement of the area of land that drains to a particular point along a stream, river, or other water body. Various reference materials differ in their attribution of the drainage area that a watershed encompasses. Although it is important to understand the U.S. Geological Survey's (USGS) Hydrologic Unit Classification (HUC) system of classifying watersheds (especially because most watershed data available for download are organized by this system), others who conduct watershed management have found that it is most effective when applied over a much smaller area than the USGS currently defines. Efforts are under way to add further levels of subdivisions to the HUC system, and states have already subdivided the smallest HUC units into smaller, more manageable ones (e.g., 12- and 14-digit HUC units).

Taking these efforts into consideration and for the purposes of this course, a watershed drainage area is defined as 20 to 100 square miles and a  subwatershed  as smaller than 20 square miles. The USGS HUC system is presented in table 1.1, along with the recommended scales for watershed management.

Watershed and subwatershed units are most practical for local watershed management plans. Each watershed is composed of many individual subwatersheds that can have their own unique water resources objectives. A water resource objective can include goals such as swimmability, fishability, and drinking water quality. A watershed plan is a comprehensive framework for applying management tools within each subwatershed in a manner that also achieves the water resources goals for the watershed as a whole. Module 4 will provide additional information about watershed and subwatershed planning scales.

Table 1.1 Comparison of the USGC HUC System with Recommended Watershed Management Scales

Drainage Area Classification System	Name(s)	Typical Drainage Area (in square miles)
USGS HUC Levels	· Region · 2-digit HUC	> 25,000
	· Subregion · 4-digit HUC · Basin	15,000–25,000
	· Accounting Unit · 6-digit HUC · Sub-basin	8,000–12,000
	· Cataloging Unit · 8-digit HUC · Watershed	500–2,000
Recommended Watershed Management Scales	· Watershed	20–100
	· Subwatershed	< 20

Source: Adapted from DeBarry (2004) and Schueler (2004)

Drainage area is a vital piece of information to use in calculating runoff volumes and discharge for a watershed or subwatershed (discussed in module 2). Drainage area is usually measured in square miles or in acres. One acre is equal to 43,560 square feet. To put this into perspective, this is about the equivalent of 70 paces by 70 paces, or the size of a football field. Drainage area is most often measured using Geographic Information Systems (GIS) but can also be done by hand using a paper map and planimeter or the square-counting method.

See the  Topographic Map Tutorial  for details on maps and for information you will need later in this module.

Determining the Size of a Watershed: The Square-Counting Method

Although this method of estimating the area of a watershed is not exact, it can provide a rough approximation relatively quickly. Basically, each different square size represents a specific area of land. By tracing the watershed boundary onto graph paper, determining what area of land each box represents, and then counting the number of squares, you can approximate the size of the watershed. The square-counting method of measuring watershed drainage area is illustrated in figure 1.2.

Figure 1.2 Square-Counting Method for Measuring Watershed Drainage Areas

Click on the image for the tutorial.

Adapted from the Center for Watershed Protection (2006); used with permission

Now try your skills with Try This 1.1.

Try This 1.1: Measuring a Subwatershed Area

In addition to the various stream network patterns and forms, urban watersheds possess an extensive network of storm drainpipes that contribute flows to the stream network. The drainage area of an urban watershed or subwatershed, therefore, is defined by this storm-drain network rather than by its topography alone. Urban drainage areas are sometimes called  sewersheds  as opposed to subwatersheds. Figure 1.3 provides an example of a sewershed.

Figure 1.3 A Sewershed

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II. Stream Order

The stream order concept was first developed by Horton (1945) and modified by Strahler (1957). Headwater streams are defined as first-order, second-order, and third-order streams. First-order streams represent the smallest drainage areas. Second-order streams are identifiable when two first-order streams come together. Similarly, third-order streams consist of two second-order streams.

Many stream order classification systems have been developed and adopted, but no single system has been universally accepted (Ward, D'Ambrosio, & Mecklenburg, 2008). For example, a classification scheme might define a third-order stream in either one of two ways:

· as the result of two second-order streams coming together, as noted above, or

· as the result of one first-order stream and one second-order stream coming together (DeBarry, 2004; Horton, 1932; Langbein & Isbein, 2011)

Headwater streams are small, but because they dominate the landscape through their sheer number and cumulative length, they are crucial in watershed management and are often the interface between land-use activities and receiving water bodies. Headwater streams are typically short and drain relatively small areas, but they are important because they make up more than 85 percent of the total stream and river mileage in the United States (Leopold, Wolman, & Miller, 1964). Table 1.2 illustrates the proportion of headwater streams to larger streams in the United States.

Table 1.2 Number, Length, and Drainage Areas of U.S. Streams

Stream Order*	Number of Streams	Total Length of Stream (in miles)	Mean Drainage Area (in square miles)**
1	1,570,000	1,570,000	1
2	350,000	810,000	4.7
3	80,000	420,000	23
4	18,000	220,000	109
5	4,200	116,000	518
6	950	61,000	2,460
7	200	30,000	11,700
8	41	14,000	55,600
9	8	6,200	264,000
10	1	1,800	1,250,000
Total	2,023,400	3,249,000	N/A
* Stream order based on the Strahler (1957) method,    analyzing maps at a scale of 1:24,000 ** Cumulative drainage area, including tributaries

Source: Leopold, Wolman, and Miller (1964)

Land-use activities directly affect headwater streams, and major receiving waters are affected in turn. As urbanization increases, streams handle increasing amounts of runoff, which tends to result in degradation of headwater streams and the tributaries to which they drain. In urbanized areas, headwater streams are sometimes filled and relocated or put into underground pipes. The photos provided in figure 1.4 below compare stream networks in subwatersheds of suburban versus urban areas.

Figure 1.4 Stream Networks in Suburban Versus Urban Areas

Source: Center for Watershed Protection (2006); used with permission

Focusing on the headwater stream level is important in watershed management for four reasons:

· Streams are exceptionally vulnerable to watershed changes.

· The public intuitively understands streams and strongly supports their protection.

· Streams are the "narrowest door" for water resource protection.

· Streams are good indicators of watershed quality.

Headwater streams can be classified as perennial, intermittent, or ephemeral, depending on how often they contain flow:

· Perennial streams generally have flow year round, even when it has not been raining.

· Intermittent streams are natural channels that tend to go dry when water tables are low.

· Ephemeral streams tend to flow only after a rainfall event.

Although intermittent and ephemeral streams may not remain "wet" year round, they are still important from hydrologic, water quality, and biological perspectives.

Do headwater streams include ditches and other artificial channels that have been created for drainage, mosquito control, or irrigation? These channels may not necessarily provide habitat (especially if they are periodically cleaned out), but it is still important to protect them because ultimately, they drain to receiving waters such as lakes, rivers, and estuaries and affect the quality of those waters. In some watersheds, these ditches are all that remain of the original stream network. The photo in figure 1.5 shows one such example from a South Carolina watershed.

Figure 1.5 Ditches in Lieu of Streams in Conway, South Carolina

Photo courtesy of the Center for Watershed Protection (2006); used with permission

Much of this watershed was formerly wetland. Ditches were (and still are) created to drain the land for agriculture or urban development. The natural drainage (wetland) has been replaced by artificial ditches that are regularly cleared of vegetation and sediment. Because of the way they are managed, these ditches do not provide aquatic habitat as a natural stream would, but essentially serve as conduits that carry runoff, sediment, and other pollutants downstream to the river. There has been a great deal of debate about whether these ditches should be protected and managed as streams, and allowed to regenerate into a more natural state to protect water quality and prevent downstream flooding.

Even where regulations protect all headwater streams, enforcement is difficult because they are not well-mapped. The "bluelines" on USGS maps show only perennial streams, and even most local mapping is done at a scale that does not capture all channels.

See the Stream Order Tutorial for details you will need in the next activity.

Let's put some of the knowledge and skills you've learned in this module to work by focusing on how to delineate subwatershed boundaries. First, look at figure 1.6, and then practice your skills in Try This 1.2.

Figure 1.6 Delineating a Subwatershed Boundary Tutorial

Click on the image for the tutorial.

Try This 1.2: Delineating a Subwatershed Boundary

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III. Watershed Regulations

In the United States, federal, state, and local governments play varying roles in the regulation of watersheds. Several federal agencies affect watersheds, including the Environmental Protection Agency (EPA), National Oceanic and Atmospheric Administration (NOAA), U.S. Army Corps of Engineers, and U.S. Fish and Wildlife Service. Some of the important regulations to consider for watersheds come from the EPA's Clean Water Act (CWA).

It is important to understand Phase I, Phase II, and the National Pollutant Discharge Elimination System (NPDES) of the CWA. Under NPDES, municipalities are requiredto implement six minimum-control measures, and these include:

· public education and outreach

· public involvement/participation

· illicit-discharge detection and elimination

· construction-site runoff control

· post-construction stormwater management

· pollution prevention for municipal operations

Note that although Phase I was designed to include larger jurisdictions, larger construction sites, and industrial activities, Phase II expanded the definition to include smaller jurisdictions and construction sites from one to five acres. Approximately 900 communities are covered under Phase I and almost 6,000 communities fall under Phase II. For more details on Phase II, refer to the fact sheet titled "Stormwater Phase II: Final Rule" provided in your reserved readings.

Often, states also have their own regulations. The combination of state departments of environment, natural resources, conservation, public works, agriculture, wildlife, and/or water resources that influences watersheds differs by state. Although state regulations are often meant to dovetail with existing federal ones, this is not always the case. In addition, local jurisdictions add another layer of regulations, sometimes at the county, city, and/or township levels. Local jurisdictions also have departments of public works, planning and zoning, environment, and so forth that add to the complexity. The combined layers of regulations can make the task of understanding, managing, protecting, and restoring watersheds difficult.

Local jurisdictions typically bear the burden of implementation in the United States because they control land use, which ultimately affects local water resources. Local governments are tasked with the job of understanding the complex assortment of regulations and figuring out how to meet them with limited budgets, staff, and technical expertise. Local jurisdictions can use a variety of tools to protect and restore their watersheds, including:

· local land-use planning

· development standards

· erosion- and sediment-control ordinances

· stormwater management practices

Regulations are important aspects of watersheds, but there are also political and social factors to consider. This includes the structure of local government, political will, citizen activism, and the importance of private-property rights issues in the community. Because both watersheds and land use involve people, understanding watersheds requires more than just knowing the science.

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IV. An Introduction to the Remaining Modules

As mentioned previously, the rest of the modules in this course focus on the science aspect of watersheds. The remaining modules are presented in the following manner:

· Module 2 provides a basic introduction to the key themes in understanding the science of watersheds. Watershed hydrology, physical properties of watersheds, water quality, and watershed ecology are discussed in detail. You will learn the importance of precipitation data, how to calculate pollutant loads using the Simple Method, how to interpret stream data, and the importance of biodiversity in watersheds.

· Module 3 provides an introduction to the impacts of urbanization on watersheds. This includes a discussion of the development process and land-use alterations; a detailed discussion of hydrologic, physical, water quality, biologic, and wetland impacts; and a presentation of the impervious cover model. You will learn to summarize the local land development process and analyze research on stream quality indicators as it relates to the impervious cover model.

· Module 4 introduces the art of watershed management and describes a variety of planning techniques and local tools for watershed protection and restoration.

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References

Center for Watershed Protection (CWP). (1998). Better site design: A handbook for changing development rules in your community. Ellicott City, MD: Center for Watershed Protection.

———. (2000). Basic concepts in watershed planning. In T. Schueler & H. Holland (Eds.), The Practice of Watershed Protection (Article 28). Ellicott City, MD: Center for Watershed Protection.

———. (2002). The do-it-yourself watershed planning kit. Ellicott City, MD: Center for Watershed Protection.

———. (2003). Impacts of impervious cover on aquatic systems. Watershed Protection Research Monograph No. 1. Ellicott City, MD: Center for Watershed Protection.

DeBarry, P.A. (2004). Watersheds: Processes, assessment, and management. Hoboken, NJ: Wiley.

Horton, R.E. (1932) Drainage basin characteristics. Transactions of the American Geophysical Union, 13, 350–361.

———. (1945). Erosional development of streams and their drainage basins—Hydrophysical approach to quantitative morphology. Bulletin of the Geological Society of America, 56, 275–370.

Langbein, W.B., & Iseri, K.T. (1960). Manual of hydrology: Part 1. General surface-water techniques (Geological Survey water-supply, paper 1541-A: Methods and practices of the Geological Survey). USGS: Science in your watershed: General introduction and hydrologic definitions. Retrieved August 16, 2011, from http://water.usgs.gov/wsc/glossary.html.

Leopold, L.B., Wolman, M.G., & Miller, J.P. (1964). Fluvial processes in geomorphology. San Francisco: Freeman.

Lumia, D.S., Linsey, K.S., & Barber, N.L. (2005, September). Estimated use of water in the United States in 2000 (Fact Sheet 2005-3051). Washington, DC: U.S. Geological Survey.

Schueler, T. (2004). An integrated framework to restore small urban watersheds (Version 1.0). Ellicott City, MD: Center for Watershed Protection.

Strahler, A.N. (1957). Quantitative analysis of watershed geomorphology. Transactions of the American Geophysical Union, 38(6), 913–920.

U.S. Environmental Protection Agency (EPA). (1994). Report to Congress on the Great Lakes ecosystem (EPA 905-R-94-004). Washington, DC: U.S. Environmental Protection Agency.

Ward, A., D'Ambrosio, J.L., & Mecklenburg, D. (2008). Stream classification (Fact Sheet AEX-445-01). Columbus, OH: Agriculture and Natural Resources, Ohio State University Extension. Retrieved August 16, 2011, from http://ohioline.osu.edu/aex-fact/pdf/AEX44501StreamClassification.pdf.