Detecting and Designing Synchronous Channel and Floodplain Habitats

Transcription

1 Detecting and Designing Synchronous Channel and Floodplain Habitats Rocko Brown, PhD ESA/ UC Davis Images: Nat Geo

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3 Synchronicity Defined: Synchronous channel-floodplains Channel and floodplain are hydrologically, hydraulically, geomorphically and ecologically connected such that key processes are coupled in time (sort of ) and space Image: TNC.org

4 Salmon ecosystems are synchronous Comparison of pre and post dam hydrology of the Trinity River with life history timing for Black Cottonwood, Narrowleaf Willow, and Fall-Run Chinook Salmon. Source: TRRP.net Key aspects of life history are coupled to seasonal changes in discharge

5 Spatial synchronicity Flashy hydrology Sediment production Mixed hydrology Sediment transfer Dampened hydrology Sediment storage Top figure from Fryirs & Brierley Floodplain forms and processes

6 Spatial synchronicity Montgomery et al Channel type and salmonid spawning distribution and abundance

7 Spatial synchronicity Montgomery et al Channel type and salmonid spawning distribution and abundance

8 We ve flipped the script! Many rural and urban rivers are partially confined via incision, development, and vegetation

9 Floodplain restoration in practice Buy land and/or set back levees Design secondary channels and floodplains within newly confined corridor Local widening Aerial view of the Bear River levee setback restoration site. Photo by Tom Griggs. Aerial view graded inset terraces on the Napa River Google Earth

10 Detecting for function As a profession we are relatively good at identifying what s wrong (provided we have the data) Use of models Advances in topographic and vegetation mapping Ecohydraulic design Over 10,000 journal articles on floodplain restoration! Journal articles discussing Number floodplain restoration Wiley (all) 5,744! Springer (all) 4,296!

11 Detrended topographic analysis Lagunitas Creek Courtesy of MMWD

12 Flow Width (ft) ,050 2,050 3,050 4,050 5,050 6,050 7,050 8,050 9,050 Source: Detrended topography derived from 2009 LiDAR data set provided from MMWD Distance (ft) ESA Project D Figure 3 Detrended topographic map of a section of the Lagunitas Creek corridor encompassing the project reach (top) and valley width series plot at 4 elevation intervals (bottom)

13 Analysis of topographic connectivity 60% 50% 40% 30% 20% 10% 0% Histogram of C(Z,W j ) for 9km of lower Yuba River Approximate Recurrence Interval (years) ,195 2,390 3,126 Discharge (m3/s) 8 m3/s 142 m3/s 597 m3/s 1,195 m3/s

14 Ecohydrologic analysis Couple salmonid ecology and hydrology to determine functional flows Coupling available flow to salmonid life cycle (Courtesy of Joe Merz, PhD of Cramer Fish Sciences)

15 Ecohydraulic analysis and design Couple salmonid habitat preference with hydraulic parameters such as depth and velocity with hydrodynamic modeling Suitability weight Depth Depth (ft) Suitability weight Velocity Depth (ft) WEIGHT Model* Ecohydraulic suitability curves for juvenile chinook salmon

16 Ecohydro analysis and design Existing Design iteration 5

17 Ecohydro analysis and design Percent Increase 300% 250% 200% 600 cfs 897 cfs 3,096 cfs 150% 100% Model results can be used to systematically 50% optimize designs before projects are built to 0% Poor assess Lowtheir worth Medium High -50% Habitat Quality Change in juvenile rearing habitat quality with discharge for the current design iteration (design 5) relative to existing conditions.

18 Syncing channel patterns Channel pattern discriminant functions expressed as a function of all relevant variables. All axes are nondimensional and thus are scale-free. (Eaton et al., 2010)

19 Syncing inset floodplains Target inset floodplain locations to coincide with riffles Riffles can help maintain connection Bed Elev. Existing Width at Qbf Residual Distance

20 Syncing inset floodplains Local widening Hypothesized Bed Elev. Bed Elev. Amplify width signal for enhancement Existing Width at Qbf Design Width at Qbf Residual Distance

21 The future is scenario analysis: what can we do with what have? Synthetic River Valleys Workflow and theory for available in Brown et al Free excel program RiverSynth available at Brown, R.A., Pasternack, G.B., Wallander, W.W., Synthetic river valleys: creating prescribed topography for form-process inquiry and river rehabilitation design, Geomorphology (2014), doi: /j.geomorph

22 The basic idea of an SRV Planform Couple plane dependent mathematical models of fluvial elements adjustable topographic models of channel-floodplain systems Profile Cross Section Brown, R.A., Pasternack, G.B., Wallander, W.W., Synthetic river valleys: creating prescribed topography for form-process inquiry and river rehabilitation design, Geomorphology (2014), doi: /j.geomorph

23 Start with topographic signatures of functional systems? Englebright Dam 9km between red bars

24 Given a corridor, what is the most optimal configuration for juvenile salmon that is also geomorphically sustainable?

25 How will managed and constructed floodplains evolve over time? Ecogeomorphic feedbacks with flow, sediment and vegetation require a holistic approach to understanding system evolution Morphodynamic models with vegetation establishment can help us Nicholas, Modeling the continuum of river channel patterns

26 Concluding remarks Floodplain restoration does not suffer from a lack of science Our ability to detect floodplain synchronicity exceeds are ability to design such environments Landscape position is key, but does it matter in the built environment when the script is flipped? Virtual test beds coupled with ecohydraulics allow us to explore possibilities and optimize what we have before we build it