Butano Creek Floodplain Reconnection and Restoration Design and Monitoring

cbec developed designs, directed construction, and conducted post-project monitoring of a project that reconnected an incised reach of Butano Creek, a tributary to Pescadero Creek, to its adjacent floodplain.

The objectives of the restoration were to: (1) allow for more frequent and longer duration inundation of the floodplain, (2) increase sediment deposition on the floodplain and reduce the amount of sediment being delivered to downstream areas, (3) promote aggregation in the channel to limit upstream incision and bank erosion, (4) provide high flow refugia for juvenile salmonids, (5) maintain fish passage through the reach, (6) increase aquifer recharge, and (7) enhance existing channel, floodplain and wetland habitats used by a variety of native biota, including several listed species including: coho salmon, steelhead, red-legged frog and San Francisco garter snake.

The design included the use of a variety of physical elements including several engineered log jams, a complex rock ramp grade control structure, as well as the in-channel recruitment of several live large riparian trees that were manipulated to form multi-complex in-channel jams. These elements add roughness to the channel, limit channel capacity, and maintain the grade of the channel bed against future incision, all of which promote greater floodplain connectivity and improve channel complexity. In addition, floodplain connector channels (breaches in a berm that runs along the edge of the channel) were included in the design to further improve low flow floodplain connectivity. cbec’s tasks included topographic and bathymetric surveys (detailed below), two-dimensional hydrodynamic modeling, scenario development and evaluation, and design calculations leading to 65% and 100% construction documents and a basis of design report. Construction occurred in 2016 and monitoring is ongoing.

Topographic and bathymetric surveys consisted of detailed cross section surveys of Butano Creek and adjacent floodplain and creekside berm. Cross sections were surveyed every 200 ft for 1.5 miles of stream channel. Select cross sections were monumented to enable repeat surveys of identical alignments to evaluate geomorphic change. Surveys were performed using a total station with local control established with RTK GPS. Subsets of this reach were also characterized with detailed 3-D surveys.