2000c). If cattle are excluded from the streams by fencing, as required by the TMDL, it is possible that the nonpoint source loading reduction goal will be met as a consequence of the riparian areas becoming reestablished. This assumes that the fences are located so that the resulting protected widths are adequate to achieve desired pollutant reductions. Width and vegetative composition need to be based on site-specific topographic and hydrologic conditions and the pollutant reductions required for each site (see Chapter 5).
The TMDL program also may lead to protection and restoration of riparian areas in those parts of the country where summertime stream temperature is an important water-quality issue. Some of the earliest stream temperature research in forested stream systems was undertaken in the late 1960s in Oregon by Brown (1969), and a significant body of knowledge has been acquired (e.g., Beschta et al., 1987) and stream temperature models (e.g., Boyd, 1996) have been developed for understanding and predicting the effects of vegetation removal on stream temperature. Temperature TMDLs are required for those waters where the instream water temperatures deviate from the state temperature standard (which in Oregon is a numeric standard based on seven-day maximum temperatures). The exercise involves identifying potential sources that contribute to increased water temperatures in conjunction with modeling efforts to evaluate the extent to which temperature improvements can be attained through improved riparian management. For example, along reaches normally occupied by a riparian forest, site potential vegetation (e.g., assumed to be late seral conifers) is utilized in a stream temperature model to indicate the potential improvements in temperature that might be realized if revegetation were to occur. Results of these analyses (e.g., Boyd et al., 1998) can be used to formulate TMDLs on a basin-by-basin basis.
The TMDL program is currently the nation’s most comprehensive attempt to restore and improve water quality (NRC, 2001). Though not a primary stated goal of the program, TMDL implementation should protect many functioning riparian areas and restore thousands of miles of degraded riparian areas along the streams and shorelines of the United States. TMDL plans for the restoration of waterbodies impacted by livestock will likely involve streamside fencing and the reestablishment of riparian vegetation. For forested stream systems, the use of riparian reserves or stream buffers of unharvested trees will become increasingly common. In addition, TMDL implementation plans for waterbodies with impairments caused at least in part by nonpoint source pollutants from cropland and pasture will likely recommend the protection of existing riparian areas that are in relatively good condition and the restoration of those that have been degraded.
As reflected in the foregoing materials, a variety of laws offer mechanisms to help protect some riparian areas or aspects of riparian areas. Few of these laws, however, reflect awareness of riparian areas as landscapes supporting multiple