Journal of Hydraulic Engineering

The functional trends of the local scour depth at a bridge pier in subcritical flow are discussed and related to flow and sediment parameters leading to a framework within which the scour depth under given conditions can be estimated. The local scour depth is shown to depend primarily on the shear velocity or mean velocity ratio to the value at the beginning of sediment movement, $u_{*}/u_{{*}_c}$ or $U/U_c\text{,}$ the grading of sediment and flow depth relative to pier width. The functions presented are based on laboratory data.

Conditions at the mouth of the Reuss River into the Lake of Lucerne (Switzerland) were considerably altered first by intensive river training works and then by dredging. The resultant shore erosion can be halted, and the original situation reestablished by recreating a natural river delta. The feasibility of this project was proven by model testing. In particular, it was possible to show that the basic concept was not only ecologically desirable but also technically sound by investigating the periodic scour and deposition patterns characteristic of a river mouth. The delta zone is separated from surrounding land by small flood dykes and a sill in the river channel which prevents backward erosion. The delta can thus be left to natural evolution processes. A plan for the first developments to realize the project was evaluated from the model tests.

Investigation of the behavior of salt solution released down a sloping surface in a tank of freshwater is reported here. Analysis indicates that the dense layer spreads in all directions at a rate proportional to the entrainment coefficient. Observations and measurements revealed a variety of phenomena depending strongly on the buoyancy flux, Richardson number, and the angle of incline. At small slope $(\sim <1/10)$ flow was found to be subcritical with negligible entrainment. As the slope increases, flow becomes supercritical and periodic interfacial instabilities appear. Growth and subsequent breakup of these instabilities were found to be the main mechanism for entrainment. Mean layer velocity away from the source can be estimated from the initial conditions and the angle of incline.

A method for predicting river channel's adjustments of equilibrium is presented and illustrated by examples. This method is based upon the quantitative relationships among the variables of water discharge, bed‐material discharge, slope, sediment size, channel width and depth for sand‐bed rivers under dynamic equilibrium. In response to changes of certain variables, the directions and magnitudes of adjustments for the others may be determined using this method. The adjustment in equilibrium may sometimes involve a dramatic transformation in channel character, or channel metamorphosis, because of certain thresholds separating channels of distinct characters. Such thresholds are intrinsic to the relationships of this method. For this reason, it is useful to identify potential dramatic changes of a river channel induced by a plan of river regulation or river control. Applications of this method are illustrated by the instability problem for alluvial canal design, adjustment of ephemeral rivers to flood, downstream changes of the Chippewa River, and the response of the lower Mississippi River to cutoffs. The cause and effect of channel adjustment for each case is elucidated.

A low velocity current meter using optical tracing of hydrogen bubbles is described. The instrument was developed for applications in hydraulic laboratory studies. Its design and operational characteristics are given. The instrument has been useful to measure velocities in the range from 0.5 to 8 cm/s.

Several methods of calculating sediment yield from agricultural watersheds are reviewed and three are applied to six Hungarian catchments where multi-year accumulated sediment yields have also been measured as reservoir deposition. The methods used to estimate sediment yields are regional regression, the Universal Soil Loss Equation (USLE) with sediment delivery ratio and a modified USLE using a runoff model. The only hydrologic data available for use are those on precipitation. Criteria for selecting a desirable procedure are presented, and, on the basis of these criteria, an event-based version of the modified USLE with rainfall data as input is deemed the best, primarily as this method results in the most accurate estimates. The other two methods gave much less accurate results with all estimation methods overestimating measured sediment yields.