Information organization

 
There are two basic strategies to organizing information for the assessment component of subbasin planning: (1) a watershed approach in which the subbasin is described in terms of hydrologic units, and (2) a stream approach that focuses on the stream reaches. Building on the region’s efforts in the Framework Project, the Council is encouraging the use of the watershed approach in subbasin planning. The Framework information will serve as a useful starting point but, in many cases, it will need to be refined and adapted to accommodate specific situations.

1. Watershed approach

In the watershed approach, the subbasin is divided into shapes, or polygons like interlocking pieces of a puzzle. Each polygon represents a drainage system consisting of a portion of the stream and the associated terrestrial drainage area. The polygon is the fundamental information repository and contains information on both aquatic and terrestrial environments.

Advantages of the watershed approach are that it explicitly integrates aquatic and terrestrial information. Also, it is relatively straightforward to incorporate spatial data from a Geographic Information System. A polygon could be characterized as having so many miles of stream with some proportion of riffles and pools and some riparian condition. In addition, the polygons could also describe land use, amount of terrestrial habitat types, wildlife species associations, road density, and so on. The system readily lends itself to consideration of watershed processes that affect aquatic conditions such as runoff, sediment movement, and land use impacts.

The most commonly used hydrologic delineation system in the Columbia Basin is the Hydrologic Unit Code (HUC) system developed by the U.S. Geological Survey. An advantage of this system is that it is inherently scaleable. By this, we mean that it is a simple matter to move from a large-scale focus, such as an entire subbasin, to consideration of finer scale issues that might occur within a small sub-watershed. In the HUC system, a large river such as the Columbia River is a HUC-2, a tributary like the John Day River is a HUC-3, the North Fork of the John Day is a HUC-4, and so on. In several recent projects the HUC-6 has been used as the principal unit for capturing environmental data. HUC-6 data can easily be aggregated to form larger scale HUCs. HUCs can also be hydrologically linked with others both upstream and downstream. This provides the capability to follow hydrological and biological processes from headwaters to ocean.

The disadvantage of the watershed system is the available level of resolution. At the present time, the system has only been delineated down to the HUC-6 level. It is possible that, for some species and some issues, the HUC-6 level will not provide sufficient detail. While finer scale considerations are theoretically possible, the process of delineating finer scale HUC units is technically complicated and is not likely to occur in the near future. However, it is possible to subdivide HUC units to accommodate local situations and increase the level of resolution.

The HUC system was used in the Council’s Framework Project in order to integrate terrestrial and aquatic systems. It was also used in the Forest Service’s Interior Columbia Basin Ecosystem Management Program (ICBEMP) for similar reasons. The course scale information provided to subbasin planners is associated with HUC-6 units for each subbasin. Planners will need to evaluate the appropriateness of the watershed approach as well as the validity of the information provided.

2. Stream approach

In the stream approach, information is associated with linear segments of a stream termed reaches. A reach is a geomorphically identifiable segment of a stream delineated between tributaries or by major changes in valley form or land use. The most elaborate system of this type is the River Reach System developed by the Environmental Protection Agency and used in the Council’s protected areas process. This system is also linked to the HUC system described above, and thus offers many of the same advantages. However, biologists also frequently devise other special-purpose reach demarcations. Mile-by-mile and pool-to-pool are two common examples. Using this system, information about the stream is associated with each reach. This includes the proportion of the reach represented by riffles, pools, and so on, as well as characteristics of the riparian zone insofar as they affect conditions in the reach. However, other terrestrial conditions are not explicitly associated with reaches.

Advantages of the stream approach are that it is relatively simple and appeals to planners and field biologists focused on specific stream habitats and fish populations. Reaches can be readily identified by field surveys or, in some cases, by the use of maps. Dissection of the stream into smaller and smaller tributaries is relatively straightforward and the level of detail is always apparent.

A disadvantage of the system is that it reinforces the division between aquatic and terrestrial planning and management. A separate system must be developed to consider terrestrial habitats and conditions. While integration with terrestrial systems is possible, it must be forced and is often not done.

Subbasin planning issues

EDT was developed with the stream approach in mind and the reach is frequently described as the basic data repository for EDT information on the stream environment. However, because both reaches and HUC-6s are linearly organized along the course of a stream, either system can be used to organize information in EDT. While EDT is typically used with a conventional stream approach, in the Council’s Framework Project, Columbia Basin subbasins were divided into HUC-6 units and analyzed using EDT.

The decision to use a particular system rests with the subbasin planners. In many cases the HUC-6 will best conform to available data and should provide results that are useful for a mid-scale initiative like subbasin planning. Because of the need to integrate terrestrial and aquatic management in subbasin planning, planners will probably find the HUC system superior to a conventional reach-based approach. It will usually be easier to work with the HUC system and refine information within this structure because of the existing work by the Council’s Framework Project. In most cases, this information and the HUC structure can be adapted to accommodate local issues of scale and resolution.

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