The Local Hydraulic And Geomorphic Effects Of Natural Large Wood Structures

1. The Local Hydraulic And Geomorphic Effects Of Natural Large Wood Structures Dr. Melinda D. Daniels Kansas State University Department of Geography

2. Morphology: What We “Understand” • Increased heterogeneity • Forced pools • Localized bed and bank scour • Channel planform stabilization (?) • Increased channel width (?)

3. Morphology: The Unknowns • How does morphologic influence change with discharge/stage/relative submergence and/or floatation? • Unrestrained wood floats • Bridging pieces may only accumulate “jams” during certain parts of a storm hydrograph • Under-flow, bed-scour

4. F.J. Magilligan et al. / Geomorphology 97 (2008) 467–482 Fig. 3. Location of LWD by zone. For LWD frequency, this documents how much wood exists in a particular zone and how many zones it spans across. For wood volume, this accounting represents how much of each segment of wood exists in each zone. Adapted from Schuett-Hames et al. (1999).

5. Upstream Downstream

6. Sediment Storage/Distributions: What We “Understand” • Buttressed wedges in high gradient streams • Step formation or reinforcement in very high gradient streams • Fine sediment retention (+CPOM, +FPOM) • Long term storage potential

7. F.J. Magilligan et al. / Geomorphology 97 (2008) 467–482 Fig. 11. Percent of all LWD associated with pool formation and with sediment storage. Sequence of basins goes from a large watershed size on the left to decreasing watershed size based on maximum drainage area of surveyed reach.

8. Sediment Storage/Distributions: Questions • Does wood really increase total storage, or does it just relocate sediment? • Particularly in moderate => low gradient systems • Are wedges just replacing bars features? • Or is there truly a net increase in storage? • Timescales?

9. Hydraulics: What We “Understand” • Roughness element • Drag, spill, form, grain • Damming effect • Backwater pool formation • Slowed velocities • Dampened helical flow in bends • Shunting of high velocity and shear stress away from banks • Zones of separated re-circulating flow

10. M. D. Daniels and B. L. Rhoads, Earth Surf. Process. Landforms 32, 460–474 (2007)

13. M.D. Daniels, B.L. Rhoads / Geomorphology 51 (2003) 159–173

14. Hydraulics: What We “Understand” • Can influence hyporheic exchange rates and spatial distribution of downwelling/upwelling • Wood removal decreases HE, but only temporarily (?) WONDZELL ET AL.: HYPORHEIC EXCHANGE AND LARGE WOOD REMOVAL, WATER RESOURCES RESEARCH, VOL. 45, W05406, doi:10.1029/2008WR007214, 2009

15. Hydraulics: Questions • How do we model: • porosity of log jams? • Floatation of pieces/jams? • Dynamic changes with Q/relative submergence? • How do we isolate wood influence on hyporheic exchange in light of strong co-variation with morphology? • How does this influence change over system response timescales?

16. How does function vary with river size, slope, stream power, supply limitation, etc.? • Large Rivers • Gurnell et al.’s work on braided river island formation

19. What are appropriate scales for effective installations? • Incorrect scales may produce little hydraulic or geomorphic effect

20. Farmington River

21. Farmington River

22. Farmington River

23. Are there thresholds that prohibit development of geomorphic complexity without the forcing mechanism of wood?