My background in civil and environmental engineering primarily emphasizes river hydraulics. In particular, one area that fascinates me is the interaction between vegetation and hydraulic properties. This may come in the form of plants influencing velocity distributions (e.g., friction of plants), or hydraulics influencing plant function (e.g., hydraulic washout of riparian trees). The following paragraphs will provide an overview of projects related to this topic.
Hydraulic Roughness Calculator (HYDROCAL): Increasingly hydraulic engineers need to understand the effects of vegetation on frictional forces in rivers (i.e., hydraulic roughness). However, the diversity of vegetation types makes frictional forces difficult to repeatedly and accurately quantify. We assembled a simple spreadsheet tool (See the bottom of this webpage) to estimate frictional forces from multiple methods proposed in the literature (pdf, 540KB).
Truckee River, May 2008. Notice the bushes and small trees on the edge of the channel.
Riparian Vegetation Washout: During extreme floods, riparian trees can be scoured or washed out. In partnership with Dr. Kumud Acharya (Desert Research Institute) and Dr. Mark Stone (University of New Mexico), our team studied the force required to washout riparian trees commonly found in the Southwestern United States. We adapted "tree pulling" techniques applied in forestry to examine windthrow potential. Knowing the forces required for failure, we can calculate the equivalent depth and velocity of water to exert this force (pdf, 400KB). We are currently developing manuscripts addressing both bending (accepted to River Research and Applications) and failure of these test trees.
"Tree pulling" experimental setup: (a) collection of frontal area exposed to flow,
(b) experimental connection to the test tree, (c) winch used in force application,
and (d) disturbed root zone (from Koizumi et al. 2007).
Wave Dissipation by Marsh Vegetation: Coastal marsh, seagrass, and algal communities can exert significant friction on waves propagating through them. In particular, coastal vegetation has the potential to significantly reduce storm surge associated with hurricanes. We are currently working with partners in the Corps' Coastal and Hydraulics Laboratory to study the dissipation of waves by coastal vegetation. As part of this project we reviewed and compiled existing literature and data (pdf, 385KB). We are now conducting laboratory studies and incoporating results into existing storm surge models.
In situ Measurement of Tree Root Architecture: Although analytical and theoretical understanding of plant-environment interaction has been made, complete mechanistic understanding of plant root architecture and function is lacking. In large part, this dearth of below-ground knowledge is driven by methodological challenges in measuring these complex biotic systems in situ (i.e., without digging up the tree). The ability to accurately measure root architecture informs countless basic research questions associated with plant growth and function as well as more applied issues such as slope stability, plant stability under hydraulic forces (i.e., during wind storms or flood events), and effects on groundwater flows. We are working with the Corps' Geotechnical and Structures Laboratory to validate new technology for measuring root architecture, namely, ground-penetrating radar and electrical resistivity. Their teams predict root architecture, and our team unearths the test tree to validate findings. This information was compiled into a series of reports on the effects of woody vegetation on levee integrity (Downloadable here).
Unearthed tree roots in Vicksburg, Mississippi, and application of pressurized air to unearth root systems in Albuquerque, New Mexico.
Alternative Methods for Bank Stabilization: I am also the principal U.S. Representative to an international working group addressing "Alternative methods for bank stabilization in inland waterways." At the request of the International Navigation Association (PIANC), this team of practitioners and researchers is assembling a state-of-the-practice review of methods for protecting river banks from erosion (i.e., How do we move beyond riprap?).
Index Velocity Methods to Predict River Flows: At the University of Illinois, I worked with Drs. Art Schmidt and Greg Wilkerson to develop "index velocity" methods for predicting velocity distributions in flooded rivers. These methods use a single measurement of velocity from a permanently mounted instrument to predict the cross-section averaged velocity for the entire channel. Most often, an empirical polynomial function is used to correlate these variables. Although also empirical in nature, our method applies a formula for predicting the depth-averaged velocity distribution, which provides a physical basis for empirical prediction (See download below).