Testing and Evaluating in a Southeast Asian Region with Precipitation Events Outside a Precipitation-Based Regional Curve Model's Typical Rainfall Range
David Bidelspach, PE
Imanthie Bandara
5 Smooth Stones Restoration, PLLC
Fort Collins, CO
Authors: Basith Weerasundara, EIT, David Bidelspach, PE, and Imanthie Bandara
Regional hydraulic geometry relationships (i.e., regional curves) have been developed for many gaged and un-gaged streams throughout the USA over the past 60 years. These regional curves are valuable for documenting the degree of departure from equilibrium of unstable stream reaches and for evaluating bankfull channel geomorphic design parameters for restoration. Regional curves are most applicable for alluvial stream systems with bankfull terraces created by sediment deposition during flow events greater than bankfull discharge. Field variability and uncertainty in identifying bankfull terrace elevations may result in inaccurate regional curves that should be used carefully in stream assessment and restoration practice. This presentation shows the results of testing a Watershed Response Factor (WRF) derived regional curve in Sri Lanka (Southeast Asia). The WRF is a scaling factor for the channel dimension vs. watershed area regional curve with a strong dependency on total annual precipitation for the region of interest. Current WRF derived regional curve development work has largely focused on geographic regions having annual rainfall totals of 0 to 60 inches/year. Kandy, Sri Lanka receives on average annual rainfall totals greater than 70 inches/year. Several stream channel measurements were taken in Kandy, Sri Lanka and the resulting hydraulic geometry relationships were obtained. These hydraulic geometry relationships from the field were compared to the WRF derived regional curve predictions. The comparison was performed to determine whether the WRF derived regional curve accurately predicts the hydraulic geometry relationships for stream assessment for areas where annual rainfall exceeds 60 inches/year. The ability to recognize a relationship, such as the WRF, or other relationships, to define design criteria more rapidly, might be used globally. The WRF would be a useful tool in developing countries; places where it is not feasible to perform a regional curve assessment; or where data, access, or funding is not available. The WRF may improve the environment in developing countries by making stream restoration possible by quickly allowing for design criteria to be developed.
About David Bidelspach, PE
David has been “Beloved” since 1977 and desires on the good days to share this love with others. He has worked and played in streams since before 2002, when he was drafted by Greg Jennings at NCSU. Nomadically, his family has lived from bags, while traveling to distant lands to work with streams, rivers and mud puddles. David’s community desire is to train others, to share the gift of ecosystem restoration and to stay in wonderment and awe of nature. Mr. Bidelspach wants to encourage others to spring up among the ordinary green grass, like willows by flowing streams.
About Imanthie Bandara
Imanthie is an intern at Five Smooth Stones Restoration and has a Bachelors’ degree in Biosystems Engineering from Asian Institute of Technology in Thailand. Imanthie is originally from Sri Lanka and now residing in Colorado. During her undergraduate studies she has volunteered with student organizations within the university and is very passionate about nature, music, and art.
Her goal of being part of the RiverSHARED organization is to be a contributor to create a process that shares good life skills/technical skills and provides learning opportunities for the underprivileged people around the world by becoming strong in her technical knowledge as a stream restoration professional and with great relationships she is gathering on the way.