21 May 2021

Approaches for Assessing Riverine Scour

Abstract: Calculating scour potential in a stream or river is as much a geomorphological art as it is an exact science. The complexity of stream hydraulics and heterogeneity of river-bed materials makes scour predictions in natural channels uncertain. Uncertain scour depths near high-hazard flood-risk zones and flood-risk management structures lead to over-designed projects and difficult flood-risk management decisions. This Regional Sediment Management technical report presents an approach for estimating scour by providing a decision framework that future practitioners can use to compute scour potential within a riverine environment. This methodology was developed through a partnership with the US Army Engineer Research and Development Center, Hydrologic Engineering Center, and St. Paul District in support of the Lower American River Contract 3 project in Sacramento, CA.

25 Jun 2020

PUBLICATION NOTICE: Quantification of the Flow Field around a Draghead Using a Physical Model

Abstract: This study quantifies the hydraulic flow field around a draghead using a 1:7 scaled California and general type draghead. The flow field velocity measurements were taken with each draghead stationary and moving with a prototype speed of 2 knots. The measured velocities increased proportionally with the pumping flow rate. Measured velocities were found to be inversely proportional to the distance from the draghead. As a result, the greatest entrainment velocities for the California draghead were measured between the two visors and below the visors. The entrainment velocities laterally of the dragheads were found to increase by a factor of 2 with the addition of either a concrete or sand bed below the draghead. The measured velocities changed dramatically when the draghead was moving with a prototype speed of 2 knots. The measurement locations to the side of the dragheads did not show the presence of fluid entrainment; instead, the velocities were dominated by the forward motion and subsequent generation of a shear layer around the draghead. The velocities behind the draghead indicated the presence of a wake behind the draghead, with the fluid moving forward at velocity equivalent to or greater than the forward translation speed.