UNIFIED WATERSHED ASSESSMENT
Purpose
The purpose of the Unified Watershed Assessment is to assess the condition of Maryland=s watersheds and, based on watershed condition, classify the watersheds into the following categories: The Unified Watershed Assessment (UWA) provides the foundation for setting watershed restoration, protection, and preservation priorities. Accordingly, the UWA needs to consider all components of the watershed related to aquatic systems including biological, physical, and chemical characteristics and related landscape factors.

Overall Goals
Two overarching goals were considered in the assessment of Maryland watersheds:

Watershed Scale
States are able to make assessments for watersheds at multiple scales under the Clean Water Action Plan, but the hydrologic unit “basins” established by the U.S. Geological Survey serve as the common scale for unified watershed assessments at the national level. There are portions of 20 of these federal basins in Maryland, with an average area in Maryland of about 500 square miles (for comparison, the average area of a Maryland county is about 400 square miles). The condition of the Maryland portion of these federal basins can be determined either directly or as a result of aggregation of assessments of smaller watersheds. Maryland has chosen the latter approach because information at smaller watershed scales will be invaluable when Watershed Restoration Action Strategies are prepared.

Maryland has identified smaller watersheds at scales that fall inside or “nest” within the larger federal basins. Assessment of smaller watersheds has concentrated on the Maryland “eight-digit watersheds”. There are 138 of these watersheds in Maryland, with an average area of about 75 square miles. Within this watershed framework, more than 1100 subwatersheds averaging 8 square miles in area are nested within the larger watersheds and are identified as the state’s “12-digit subwatersheds”. Identifying intensive monitoring and restoration activities by state or local governments or non-governmental organizations within these smaller subwatersheds may be desirable.

Watershed Assessment Methods

Clean Water Goals
For the Clean Water Goals mentioned above, the assessment generally examined single factors that result in, or cause, a violation of the numeric/narrative water quality standards. The primary tool used to assess whether watersheds were within the numeric/narrative water quality standards was the list of impaired waters generated under Section 303(d) of the Federal Water Pollution Control Act (NOTE: In compiling this list, the Technical Workgroup relied upon the April 1, 1998 draft of the State’s 1998 303(d) list). This list was prepared with reference to all readily available data, including the information compiled in the development of Maryland’s Water Quality Inventory Report under Section 305(b) of the Act.

Other Natural Resource Goals
For the Other Natural Resource Goals, the assessment generally evaluated the multiple and cumulative impacts that prevent watersheds from achieving healthy watershed conditions as expressed through natural resource indicators such as those listed below. These indicators relate to the condition of water chemistry, aquatic living resources, physical habitat and landscape. Assessments have initially been done using existing data from state monitoring and assessment programs. These data constitute the core data for the Unified Watershed Assessment. In addition, supplemental information has been solicited via a mailer sent to several hundred individuals and organizations, such as local governments and community watershed associations, encouraging them to submit available watershed assessments. Significant supplemental data have been received and are being evaluated and applied to continuing assessment and prioritization activities.

Category 1

Both the violation of water quality standards, as reflected by inclusion on the 303(d) List, as well as poor values for other natural resource indicators, are used as criteria for determining whether a watershed is classified into Category 1, “in need of restoration”:

Category 1(a): Those waters that appear on the 303(d) List are identified in Category 1(a). These waters require restoration in order to meet water quality standards. In addition, some of these watersheds may require restoration in order to meet other natural resource goals.

Category 1(b): Those waters that are not on the 303(d) List, but require restoration in order to meet other natural resource goals are identified in Category 1(b).

Many data sets that could be used as natural resource indicators were examined. A minimal number of indicators was selected that would provide the most accurate, nonduplicative, and comprehensive assessment of watershed condition. These indicators could be grouped into several major “clusters” that focused on the key areas of watershed condition:

Water Chemistry

Aquatic Living Resources Landscape (The data sources for these indicators and their methods of calculation are discussed in the “metadata” in the Technical Appendix. The indicator data for each watershed are listed in Table 1. (NOTE: A set of "watershed profiles" for each of the 138 watersheds is available in a (138 page) Watershed Profile Appendix to this report. Each profile includes a more detailed map of the watersheds, including subwatershed boundaries, and a summary listing of data for the watershed.). Benchmarks (thresholds) for the indicators are listed in Table 1a.)

To determine whether a watershed does not meet a Natural Resource Goal, one of two types of decision-making criteria is used:

An indicator value does not meet an established goal or benchmark level (e.g., a Non-tidal Fish Index of Biotic Integrity (IBI) less than 6 indicates that the fish communities in a watershed’s streams are in poor condition. This would result in a Category 1 rating for that indicator); and

An indicator for which there is no established goal or benchmark level has a value among the worst 25 percent of all watersheds assessed by that indicator (e.g., a watershed whose percent of impervious surface was among the highest (i.e. worst) 25 percent for all the watersheds would place that indicator in Category 1). Thus, the worst 25th percentile serves as the Category 1 benchmark for this type of indicator.

Application of these criteria is also described in the metadata forms in the Technical Appendix.

Category 3

Some of the indicators for Category 3 (i.e. pristine or sensitive) Watersheds are similar to the indicators for Category 1 (i.e. not meeting goals) Watersheds; others are different. For example, there are no tidal watersheds that are considered to have particularly pristine or sensitive benthic communities. Therefore, the Tidal Benthic IBI is not used for Category 3. Conversely, some new indicators appear in assessing watersheds for Category 3 classification. For example, trout spawning areas are an indicator of relatively pristine natural conditions, so presence of trout spawning is a useful indicator for Category 3. However, absence of trout spawning areas does not necessarily imply that a stream is degraded - it may never have had the natural conditions which are prerequisite for trout spawning. Therefore this indicator is not useful for Category 1. Some indicators can be clustered under key living resource and landscape issues and others address special water use needs (i.e., drinking water and fish hatchery water supply).

Living Resources

Landscape (Benchmarks (thresholds) for the indicators are listed in Table 1b. Application of these indicators is also described in the metadata forms in the Technical Appendix.)

Results
The results of this draft Unified Watershed Assessment for Maryland are displayed in Tables 2 through 4, which list those watersheds that have been placed in Categories 1 through 3, and Figures 1 and 2, which map the locations of watersheds that have been placed in Category 1 (needing restoration) and Category 3 (pristine or sensitive and needing special protection). In addition, Table 5 contains a complete listing of which indicators fail to meet a Category 1 criterion for each watershed. The procedures for assigning watersheds to each of these four categories are as follows:

- Category 1 Watersheds (Table 2 and Figure 1):

Category 1(a): Any watershed on the 303(d) list. (These watersheds may also have natural resource indicators failing to meet Category 1 benchmarks.)

Category 1(b): Any watershed not on the 303(d) List and having two or more natural resource indicators failing to meet the Category 1 benchmarks.

- Category 2 Watersheds (Table 3):

Any watershed that is not on the 303(d) List (Category 1(a)) and meets all or all but one of the Category 1(b) benchmarks was placed in Category 2.

- Category 3 Watersheds (Table 4 and Figure 2):

Any watershed with two or more indicators meeting Category 3 criteria was placed in Category 3. Furthermore, those watersheds with four or more indicators with a Category 3 rating were highlighted as “Selected Category 3 Watersheds” (Figure 2b). (Although it had only three indicators meeting Category 3 criteria, Seneca Creek has also been included as a Selected Category 3 Watershed. This is based on detailed watershed studies submitted by Montgomery County, as well as state monitoring data, which indicate that Seneca Creek has exceptionally pristine headwater streams.)

- Category 4 Watersheds:

The federal Clean Water Action Plan also identifies a Category 4 - Insufficient Data - Watersheds for which there is insufficient data to classify the watershed into Categories 1, 2 and 3. Although the amount of data available for different watersheds varies, Maryland has sufficient data to classify all of its watersheds into Categories 1, 2 and 3 (at least on a preliminary basis).

In aggregating information from the smaller Maryland watersheds to the larger federal basins, guidance from the federal Clean Water Action Plan was followed: federal Category 1 Watersheds include those federal basins where the area of Maryland Category 1 watersheds comprises at least 15 - 25 percent of the area of the federal basin. This turns out to include all of the federal basins in Maryland with any significant size.

A number of state watersheds fall into both Categories 1 and 3. This is not unexpected, since land use and related factors in a single watershed may vary considerably. For example, a watershed may have undisturbed headwaters but be significantly developed at its mouth. Therefore, unless the watersheds are assessed at a scale where the land use is relatively homogeneous (NOTE: As Montgomery County has done in its Countywide Stream Protection Survey, where 200 subwatersheds having relatively homogeneous land use were selected for the assessment), Category 1 and Category 3 are not mutually exclusive, and state watersheds are listed under both Category 1 and Category 3 if the indicator values so warrant.

On the other hand, our understanding of the UWA Category system, as it will be employed at the federal level, is that a watershed (i.e. federal basin) can be placed in only one of the 4 Categories. In addition, it is our understanding that if a federal basin has characteristics of both Category 1 and Category 3, it will be listed as Category 1 in the federal compilation. Therefore, for purposes of reporting results aggregated to the level of the federal basins, we place each federal basin only in one category, Category 1.

Evaluation of the available data, some of which is preliminary, will continue. It will be supplemented by comments and suggestions from the public workshops, additional local and regional watershed data (examples to date include information recently submitted by the MD Bureau of Mines related to watersheds affected by acid mine drainage in Western Maryland, as well as a number of watershed studies submitted by local governments) and data obtained through mutual exchange with surrounding jurisdictions for interstate watersheds (NOTE: The importance of coordinating with adjacent states with regard to interstate watersheds is illustrated in Figure A1 in the Technical Appendix, which shows the total watershed areas, including those portions outside of Maryland, for the 20 federal basins occurring in Maryland.). As these activities progress, Maryland’s Unified Watershed Assessment can be expected to undergo modification. Finally, a major effort is underway to finalize the development of statewide indicators of the potential impacts of projected growth on watershed resources. This effort will allow us to take advantage of the Clean Water Action Plan process to coordinate activities for Smart Growth and watershed protection, so that both efforts can be successful in the long term.

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