Since the 1850s Sierra Nevada watersheds have experienced a variety of intensive land uses which have impaired natural processes (Kattelman 1996; Kondolf et al. 1996). One widespread result of combined stressors has been degradation of moist meadow areas into dry "flats" with incised channels (Kattelman and Embury 1996). Meadow degradation has adversely affected wildlife and fisheries and decreased the ability of watersheds to store water and sediment leading to downstream changes in flood peaks, erosion, and sedimentation.
Restoration and rehabilitation of watersheds and meadows have been ongoing activities in the Sierra Nevada since the 1930s but effectiveness of these projects is uncertain because of a lack of monitoring. Presented below are conceptual models developed to facilitate meadow restoration effectiveness monitoring in the 55,000 acre Last Chance Creek watershed, a tributary to the North Fork of the Feather River. This basin has been chosen as a focus for intensive restoration and monitoring by the Feather River Coordinated Resource Management group in cooperation with University of California Cooperative Extension.
The models are based on literature review and local group expertise. They constitute a set of hypotheses, which will be "tested" by future restoration activities in the watershed. They may be refined after a detailed watershed analysis has been conducted. You are invited to address comments on the models to rrharris@nature.berkeley.edu or mjdelasaux@ucdavis.edu.
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Model One describes the key physical components of the Last Chance Creek watershed; the natural disturbance and hydrologic processes working on these components; and how these relate to key watershed assets which benefit human users.
Key elements of the natural disturbance regime are frequent low intensity fires, seasonal grazing by indigenous ungulates (Burkhardt 1996), and periodic extreme rain-on-snow precipitation events. The meadow/floodplain/valley complex of the watershed is integral to water and sediment storage. The functions of this complex at different elevations and scales are similar, although the overall influence on hydrologic pattern change with size and elevation. In low gradient areas, stream waters slow, causing sediment to drop out along the stream channel forming riparian meadows and floodplains. High water tables in these areas encourage riparian vegetation, which in turn, stabilizes stream channels and helps capture and store sediment. Key assets for human users are created through the interaction of these processes, and the resulting relatively stable meadows, channels, and uplands. Groundwater stored from winter precipitation is discharged as summer baseflow benefiting irrigators, instream life and hydropower generators. Floodplains act as water storage areas during floods, dampening downstream peaks. Riparian vegetation in meadows, maintained by high ground water levels, stabilizes channels and provides forage for wildlife and livestock. Channel "stability" creates aquatic habitat for fish and aquatic organisms and maintains a natural rate of sediment production to downstream areas.
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According to Noon (1997), conceptual models should demonstrate linkages between environmental stressors and system components. Stressors affect watersheds by changing disturbance regimes and adding new disturbances. Together these change sediment and water transport and storage processes which leads to changes from natural conditions that have negative impacts on watershed assets and users. The cumulative effects of these changes are displayed in Model Two. At Last Chance Creek, the changes have combined to reduce the watershed's ability to store water and sediment and to reduce upland and channel stability.
Stressors in the Last Chance Creek watershed include changes in the natural disturbance regime due to overgrazing by livestock and decreased fire frequencies. These changes, in combination with new stressors including logging, mining, water supply and floodplain development, have caused changes in the watershed. Channelization has increased water depth and velocity, and thus channel erosion. Down-cutting of stream channels drains surrounding lands more quickly, desiccating the shallow groundwater table in meadows. Drier conditions ey lead to replacement of riparian vegetation by species adapted to dry sites such as sage brush. Reduction of riparian vegetation decreases channel stability, decreases shade canopy and increases stream temperature, degrading habitat for fish and aquatic organisms.
Degradation of meadows reduces the watershed's ability to store water. Discharge patterns become "flashier" with water reaching the stream faster with more erosive energy. Extreme precipitation events are expressed differently by the changed system. Large events have more erosive power and carry more sediment through the system because more sediment is delivered to the channel.
Reduced capacity to store water in floodplains and meadows leads to higher peaks during winter flows and lower baseflow in the summer season. These effects decrease channel stability and, together with reduced upland stability, increase sediment yield from watersheds affecting downstream hydropower generation, channels on downstream properties, and aquatic habitat.
Reduced summer stream flow leads to higher stream temperatures which degrades habitat for fisheries and aquatic organisms. It also reduces water quantity for summer hydropower generation and downstream consumption. Flashier discharge increases downstream flood damage.
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Ideally, restoration would consist of removing watershed stressors, allowing watersheds to return to a natural disturbance regime over time (Ebersole et al. 1997). However, in many cases, relief of stressors alone may not be enough to restore the watershed to a desired condition. Restoration should then be targeted to mitigate against changes in key hydrological processes caused by stressors.
Model Three describes how revegetation projects attempt to reverse the negative consequences on channel stability from loss of riparian vegetation. Clearly, an isolated revegetation project is inadequate in scale to reverse the changes in the Last Chance Creek watershed hypothesized in Models One and Two. The measures diagrammed in Model Three should be considered as one small part of an overall restoration effort conducted at appropriate scales and locations. No attempt has been made to portray the relative size of each process or component in the model.
Riparian vegetation increases the strength of stream banks and promotes infiltration and sediment deposition. Relief of the grazing stressor coupled with revegetation and soil tillage may restore floodplain roughness thereby encouraging sedimentation and bank building, increasing stream bank strength and infiltration, leading to an increase in channel stability.
Effectiveness monitoring of a proposed revegetation project may be focused by use of Model Three. According to Noon (1997), indicators chosen for measurement in the monitoring program should reflect known or suspected cause and effect relationships among system components. His criteria for indicator selection include reflection of underlying processes and changes in stressor levels; representativeness of the larger resource, and ability to be quantified. Monitoring of the revegetation project diagrammed in Model Three would focus on the processes the project is attempting to affect: riparian vegetation growth, infiltration, stream bank deposition, and discharge velocity.
Burkhardt, J.W. 1996. Herbivory in the Intermountain West: an overview of evolutionary history, historic cultural impacts and lessons from the past. Idaho Forest, Wildlife and Range Experiment Station Bulletin Number 58, College of Forestry, Wildlife and Range Sciences, University of Idaho, Moscow, Idaho, 35 pp
Ebersole, Joseph L., Liss, William J., Frissell, Christopher A., 1997. Restoration of stream habitats in the Western United States: restoration as re-expression of habitat capacity, Environmental Management 21:1-14.
Kattelmann, R. 1996. Hydrology and water resources. P. 855-920 IN: Volume II Assessments and Scientific Basis for Management Options, Sierra Nevada Ecosystem Project. Wildland Resources Center Report No. 37, University of California, Davis.
Kattelmann, R. and M. Embury. 1996. Riparian areas and wetlands. P. 201-274 IN: Volume III Assessments, Commissioned Reports, and Background Information, Sierra Nevada Ecosystem Project, Wildland Resources Center Report No. 38, University of California, Davis.
Kondolf, G.M, R. Kattelmann and M. Embury. 1996. Status of riparian habitat. P. 1009-1030 IN: Volume II Assessments and Scientific Basis for Management Options, Sierra Nevada Ecosystem Project, Wildland Resources Center Report No. 37, University of California, Davis.
Noon, B. 1997. Conceptual issues in the monitoring of ecological resources, working draft. Unpublished report of the USDA-Forest Service Redwood Sciences Laboratory, Arcata, California, 57 pages
