Bryan M. Dick, PE, PH Ph.D. Student - North Carolina State University President Lotic Solutions LLC, Austin, TX, USA

Transcription

1 Bryan M. Dick, PE, PH Ph.D. Student - North Carolina State University President Lotic Solutions LLC, Austin, TX, USA Dr. Ilona Peszlen & Dr. Perry Peralta North Carolina State University Dept. of Forest Biomaterials bmdick@ncsu.edu

2 Outline of Presentation Background information Real world scenarios Previous work and literature Materials and Methods Results Conclusions and Recommendations

3 A few examples of why accelerated erosion is a concern

4 Threats to Infrastructure

5 Loss of Channel Capacity

6 Contaminated Sediments

7 Excessive sediment as leading cause of impairment of the nation s waters (EPA 2006) Streambank erosion accounts for 90% of total annual sediment yield in rivers.

8 Critical questions on impaired/contaminated rivers: 1. Rate of streambank erosion 2. Total annual quantity of sediment from eroding streambanks

9 Direct measurement Time trend analysis of historic aerial photographs and maps Sedimentary/biological/ biochemical (Lawler 1993) Analytical models Empirical models BANK PINS

10 Empirical models BANCS: Erosion rate curves with bank-level data of Near Bank Stress (NBS) and Bank Erosion Hazard Index (BEHI) to predict sediment entrainment rates across an entire reach But: Erosion rate curve must be developed from other method

11 Dendrogeomorphology: Use of tree growth rings to identify dates of changes in earth surface processes Basic Concept Tree rings change in response to environmental factors (e.g.landslide, streambank and hillslope erosion) Change reflected in growth rings Count number of rings to find date of geomorphic change webdocs.dow.wur.nl/internet/fem/uk/_images/zyadin_project3_big.jpg

12 Most dendrogeomorphic applications use stem of tree Small set of research focused on exposed tree roots American hardwood species seldom used Very little application of method to streambanks No studies have used this method to develop erosion rate curves

13 Majority of previous research conducted in Europe Virtually no research performed on responses to exposure in American hardwood species Very little application of method to streambanks No studies to date using method to develop erosion rate curves

14 To use dendrogeomorphic root analysis in order to hindcast and forecast the erosion of a river banks in central Michigan, U.S. develop an erosion rate curve to predict erosion rates anywhere on river Relate results to locally assessed Bank Erosion Hazard Index (BEHI) Validate results via comparison to direct measurement

15 Data collection on T. River: 78 samples collected 24 different bank locations 15 miles of river sampled Study and control samples collected primarily from three species: Hackberry (Celtis occidentalis ), sugar maple (Acer saccharinium), Eastern cottonwood (Populous deltoides

16 Measured horizontal distance between root and river bank Multiple samples obtained from each tree Control samples collected from buried portion of root Some roots collected on same bank as erosion pins at 5 locations Rated each bank with a Bank Erosion Hazard Index # Erosion Pin

17 Ratio of Study Bank Height / Bankfull Height (7.7 ft/ 4.0 ft) = Ratio of Root Depth / Study Bank Height (5.0 ft / 7.7 ft) = Weighted Root Density = Root Density % X (Ratio of Root Depth / Study Bank Height) X 0.64 = 38 Bank Angle Surface Protection 100% 0.0 Bank Material Adjustment (Sand bank adjustment) 5.0 Total Score 23.5

18 SCAR ECCENTRICITY SCAR Eccentric growth (indicates presence of reaction wood, which forms in response to pull of gravity on root) Scars- indicates exposure/physical damage from external force

19 Root samples prepared for microscopic analysis Microscopic slides of microns were cut and stained with safranin Digital images were taken and analyzed to find the year of exposure Average annual erosion derived from known distance to bank and years of exposure

20 Diffuse Porous-Sugar Maple Ring Porous- Slippery Elm BEFORE EXPOSURE BEFORE EXPOSURE AFTER EXPOSURE Decrease in size and increase in number of cells in post-exposure rings AFTER EXPOSURE Change from diffuse-porous structure to ring porous and stem like structure

21 Average erosion rate as a function of the BEHI Score for (a) all root samples (R ), (b) root samples exposed 10 years or less (R ), (c) root samples exposed 7 years or less (R ), (d) root samples exposed 5 years or less (R ). Dick et al. 2013

22 Erosion Rate (ft/yr) Avg. Erosion Rate (ft/yr) Erosion Rate vs. BEHI Score for Samples on Buffalo Bayou y = 3E-06x R² = BEHI Score Erosion Rate vs. BEHI Score for Samples on Halls Bayou y = e x R² = BEHI Scores

23 Fagus americana (American Beech) Rapid decay limits use Fraxinus americana (Green Ash) - obvious indicators GOOD Carya aquatica (Water Hickory) - Good Populus deltoides (Poplar) can be tough to see but consistent Salix nigra (Black Willow) also tough but useable, esp. at 40X Quercus nigra (Water Oak) obvious indicators GOOD Celtis occidentalis (Hackberry) GOOD Pinus taeda (Loblolly Pine) Problematic False Rings

24 4x Before After

25 Fraxinus SRP (or SDP) 4x Before After Wide annual ring vs ring width 1/3 or less

26 Populus - DP 4x Transition 40X Buried Buried Consistent for all species evaluated: Cell wall thickening Reduction in fiber lumen diameter 40X Exposed

27 Tree root analysis has great potential as tool to quantify extent and magnitude of stream bank erosion Eastern hardwood species respond to exposure in a predictable manner The occurrence of eccentricity in growth rings (still investigating) Transition of diffuse to ring porous arrangements of vessels (root-like to stemlike anatomy) Dramatic increase in annual ring width Decrease in the size of vessels and fibers, fiber cell wall thickening Occurrence of gelatinous fibers Occurrence of pith flecks (scarring and wound tissue). Advantages : Extensive data sets Erosion rates determined quickly Long term erosion trends can be analyzed

28 Limitations More recently exposed roots are better for prediction with BEHI Difficult to obtain samples on banks with worst and least susceptibility to erosion (either no exposed roots, or no trees left on bank)

29 My colleagues at AECOM Dr. Orsi Bencze Dr. Laszlo Horvath

30 Dick, B. M., Hey, R., Peralta, P., Jewell, I., Simon, P. and Peszlen, I. (2013), ESTIMATING ANNUAL RIVERBANK EROSION RATES A DENDROGEOMORPHIC METHOD. River Res. Applic.. doi: /rra.2682 den Ouden, J., Sass-Klaassen, U.G.W., Copini, P., Dendrogeomorphology a new tool to study drift sand dynamics. Geol Mijnbouw- N J G. 86(4),