Design of a channel and floodplain corridor to restore aquatic habitat, geomorphic function and water quality in an urbanized and regulated watershed

0
The City of Cupertino, California has proposed the establishment of the Stevens Creek Corridor Park. At the park site, Stevens Creek has an incised alluvial channel. Bed morphology is typified by riffles and pools with some external forcing by in-stream large woody material. The channel has been subjected to hydromodification and general anthropogenic disturbance due to upstream reservoir operations, construction of in-stream obstructions, and changes in land use.  Land use around Stevens Creek has changed considerably over the last 50 years from primarily orchards to urban neighborhoods and parks. The objective of the project is to improve upon existing in-stream and riparian habitat and associated hydrologic and geomorphic function. To address this objective, we have proposed the removal of four existing fish-migration barriers, channel realignment, construction of riffles and pools based on existing and stable channel forms located upstream of the project reach, installation of fishery-related habitat structures such as Jhooks and large wood elements, and bio-technical slope stabilization measures such as brushlayer fill slopes. Design methodology and analysis included: (a) soil trenching of terrace sediments, (b) a geomorphic survey and analysis of the design reach and reaches upstream and downstream, (c) channel layout alternatives analysis, (d) hydraulic modeling of existing conditions and proposed design conditions, and (e) sediment transport computations of design geometries. The design is scheduled for implementation in summer 2008.

INTRODUCTION
The City of Curpertino, California has proposed the establishment of the 60-acre Stevens Creek Corridor Park which includes realignment of 1,283 feet of existing channel and rehabilitation of in-stream and riparian function and habitat. In the park, Stevens Creek has an incised alluvial channel. Bed morphology is typified by riffles and pools with some external forcing by instream large woody material. The project reach of the creek has several man-made drop structures that act as both partial and complete barriers to fish migration and have led to channel bed and bank erosion downstream.

At the park site (Figure 1) flow in Stevens Creek is regulated by Stevens Creek Reservoir, located approximately two miles upstream and completed in 1935. Stevens Creek reservoir acts to trap sediment and reduces the effective contributing area of sediment from 19 square miles to 2.5 square miles. Land use around Stevens Creek has changed considerably over the last 50 years from primarily orchards to urban neighborhoods and parks. As such, Stevens Creek has been subjected to hydromodification and general anthropogenic disturbance due to reservoir operations, construction of in-stream obstructions, and changes in land use. Given all the historic cumulative impacts to natural hydrologic and geomorphic process, it would be impractical to attempt to restore the channel to pre-dam or pre-urban form and geometry.

However, geomorphic function and habitat can be improved. Fifty-percent construction documents have been completed and the design is scheduled for implementation during the summer of 2008.

Customer comments

No comments were found for Design of a channel and floodplain corridor to restore aquatic habitat, geomorphic function and water quality in an urbanized and regulated watershed. Be the first to comment!