Prioritizing Alluvial Reaches for Riparian Corridor Expansion, Protection, and Restoration

Scenario Framework

Key Management Questions:

• Within a given stream reach, which areas are suitable for expansion of the riparian corridor, based on ecological and socioeconomic criteria?
• Of the selected areas, which are suitable for purchase of fee title, placement of a conservation easement, restoration, or other methods of enhancement?

Topic: Prioritizing alluvial stream reaches for riparian corridor expansion, protection, and restoration.

Purpose: To determine which areas provide the best opportunities for expansion of the riparian corridor, as well as the viability of various options.

Disclaimer: This scenario was developed for illustrative purposes only. No actual land use/land cover changes are implied or proposed.

Context: Natural resource managers must often choose between several options for restoration projects. Limited funding, time, and personnel coupled with differing reach conditions make it necessary to prioritize potential projects in terms of both restoration potential and resource constraints. For this module, it is assumed the decision maker is targeting the expansion of the riparian corridor as a salmonid recovery measure. The module presents a method for determining which streamside areas are suitable for riparian corridor expansion and a framework for deciding which of those areas are most conducive to restoration, preservation or enhancement projects. The geographic focus of this module is the San Lorenzo River watershed, which contains land uses, topography, and plant communities representative of San Mateo and Santa Cruz Counties.

Audience/User: Coastal managers, watershed groups

Geographic Setting: San Lorenzo River watershed

Limiting Factors Addressed: Water temperature, large woody debris, habitat quality, substrate/sediment conditions

GIS Data Sets Required: Aerial photography, land use/land cover data, hydrography, and other base data (user-determined). To access some of these data sets, go to the SRP GIS Data Inventory section of this Web site.

Nonspatial Data: Land costs, restoration cost estimates, invasive plant removal cost estimates, area-specific plant and animal species lists, area-specific endangered plant and animal species lists.

Background:
Intact riparian corridors, consisting of streams and the adjacent riparian habitat, are critical to the viability of salmonid populations and support some of the highest levels of biological diversity in the world (see the Riparian Habitat section for more information). In wide alluvial floodplains, these corridors have historically supported floodplain riparian forests that provide nutrients, shelter, thermal regulation, and other elements critical to both the aquatic and terrestrial environments. When these corridors are wide enough to be sustainable over the long term, they will also serve to buffer streams from sediments and pollutants and to provide for long-term recruitment of large woody debris into the streams (for more information, see the Factors Limiting Salmonid Production section of this Web site).

In many parts of California, however, the natural geomorphic and hydrologic features of wide alluvial floodplains have been modified, and the riparian habitat has been lost to urban development, agricultural expansion, and gravel mining. These areas are more likely to experience land use/land cover change than geologically confined reaches of the riparian corridor, like narrow canyons, because they’re easy to develop, they’re desirable sites for housing, their rich soils have high agricultural value, and the underlying aggregate material is high in quality and, therefore, economic value.

Restoring riparian corridors requires an assessment of existing conditions on the landscape scale. This assessment is best accomplished through spatial analyses using geographic information systems (GIS) with site-specific evaluations of a wide array of ecological and socioeconomic factors. This scenario shows how spatial and other data can be used to set priorities for riparian corridor expansion, protection, and restoration. Three important steps are outlined:

1. A qualitative assessment of the landscape using an aerial map,
2. A quantitative assessment of the landscape using land use and land cover information, and
3. A quantitative analysis that incorporates ecological and socioeconomic factors.

In addition, a supplemental qualitative analysis step is included for choosing the appropriate restoration effort level and mode of property acquisition.