Journal of Hydraulic Engineering

Experiments are conducted in a horizontal laboratory channel with slightly diverging walls to simulate buoyancy driven plunging flow. A temperature difference between inflow and downstream ambient provides the density differential that initiates the underflow. Temperature profiles and flow visualization are used to determine flow conditions in the plunge region. Channel divergence angles (half‐angles) from 1–15° are investigated. Volumetric flow rates in the sinking flow increase from 0–45% during the plunging process. Maximum entrainment rates are nearly linearly related to divergence angle. Depths of the underflow downstream from the plunge line are from 0.65–0.9 times the depth at the plunge line. Densimetric Froude numbers from 0.56–0.89 occur at the plunge line, depending on the channel divergence angle and the discharge densimetric Froude number. A flow analysis that explains and supports the experimental data is presented. Channel expansion affects the plunging process significantly, particularly entrainment rates and densimetric Froude numbers at plunging.

The bed degradation in alluvial channels resulting from sediment interruption is simulated numerically by solving the one‐dimensional momentum and continuity equations for water and sediment. A simple “bed layer” model is proposed to simulate the plane bed armoring process; the model does not contain any parameter that needs calibration. The agreement between the numerical results and the available experimental data is satisfactory.

A model for least cost design of regional stormwater detention networks is developed to aid in identifying cost‐effective regional detention basin sites within watersheds undergoing urban development. The model, through the application of dynamic programming techniques, is designed to minimize the cost of required facilities while meeting the hydrologic and hydraulic constraints of the watershed. For this study, model inputs include storage‐elevation relationships at each candidate detention basin site, maximum permissible flow in each channel reach, land and dam construction cost functions, watershed hydrologic routing parameters, and design storm hydrograph parameters. The model can be applied to watersheds with multiple branching and existing detention basins. The program is applied to a 16.5 sq mi $\left(42.7{\mathrm{km}}^2\right)$ watershed in Austin, Texas. Eight existing and five candidate basins are considered.

The stability of rock protection on slopes attacked by a flow requires two conditions. The first is the resistance to sliding that is provided if the ratio of tangential forces to normal forces on one or several rock layers is less than the tangent of the angle of friction of the layers on their support. The second is the resistance to wrenching of the surface layer blocks and is covered by equations derived from the Shields criteria. This paper proposes a new approach to two factors in the analysis, namely: (1) For downslope flow the hydrostatic pressure gradient is not vertical but normal to the slope, and thus existing equations expressing the effect of slope on the threshold shear stress are modified; and (2) a condition of stability that involves the bearing angle of a surface‐layer block thrusting on neighboring stable blocks that is wider than the commonly used angle of repose.

A laboratory study is conducted to determine the flow parameters of a rectangular surface jet discharging normally onto a cross flow. The Reynolds numbers of the buoyant jet and the cross flow are $11\times {10}^4$ and $7.4\times {10}^4\text{,}$ respectively, with a densimetric Froude number of 1.7 and a ratio of ambient velocity to jet velocity of 0.9. Vertical and horizontal isotherms are determined, and it is found that the jet axis is strongly depth‐dependent. Profiles of the mean velocity and the temperature turbulence intensity are measured at various downstream sections. Lateral profiles of the temperature flatness factor, skewness factor, temperature length scale, and the warm water flux are measured at one cross section. The transport of warm water by large‐scale structure is discussed.

The unit hydrograph is a widely used method for hydrologic design. However, there is a general lack of understanding about the accuracy of the unit hydrographs used in urban areas. Analysis of storm data from seven urban watersheds in Los Angeles provide the basis for evaluating the variation of dimensionless S-hydrographs with both storm event and location. The results of the analysis provide a generalized dimensionless S-graph that should be applicable on urban watersheds.