Journal of Hydraulic Engineering

Field measurements have been made of the turbulent fluctuations of the longitudinal and vertical components of velocity by using an electromagnetic flowmeter in a partially mixed reach of the Great Ouse estuary. An error analysis of the results showed that the measurement technique was satisfactory for determining most turbulence parameters. The effects of stratification were clearly apparent in the length scales, energy spectra, and cospectra of the turbulent fluctuations. The characteristics of the turbulence were found to be similar to those for laboratory flume data and stably stratified atmospheric boundary layer data for various specific conditions. More data are required to cover a wider range of conditions.

In order to address questions relating to the cause of local flooding in many downstream watersheds in Houston, TX, a computer model has been developed that handles both a surcharged pipeflow condition and a variable tailwater in the outflow. The ILLUDAS model has been adapted to accept surcharged conditions through the incorporation of an iterative hydraulic grade line calculation, which then allows a corrected set of flows through the pipe system. A variable tailwater condition corresponding to a known or predictable flood hydrograph in the main channel is also included. The pressurized ILLUDAS backwater simulator (PIBS) provides a useful extension of ILLUDAS to areas that suffer from surcharge flooding in low‐slope areas, such as the Gulf Coast. The model has been compared with the extended transport model (EXTRAN) for a 53‐pipe storm sewer system, and excellent agreement for the outflow hydrograph was shown under surcharged conditions. The model has been applied to 500 pipes in the Texas Medical Center and Rice Univ. in Houston, TX, which are adjacent to one of the main flood channels. Results from the analysis indicate good agreement with the observed street ponding locations in the area for high‐intensity rainfall events.

Relations are developed for use in estimating the momentum and energy coefficients of flow over submerged grass channel linings. The proposed relations have their basis in Prandtl's mixing length approach to momentum transfer but are reduced by curve fitting to a form suitable for direct computer solution. The independent variables are those routinely calculated in grass‐lined open channel design.

Until now no solution was available to determine the effect of plane drainage located anywhere between two end cutoffs of a flat floor founded on permeable soil of finite depth. An exact solution has been obtained using conformal mapping. Equations for uplift pressure below the floor and for exit gradient are given. The equations are solved numerically to obtain pressures at key points and at the exit gradient. The results are given in the form of easy‐to‐use design curves. The uplift pressures reduce considerably along the structure's entire profile with the provision of filtering even very small lengths. The uplift pressure, in general, decreases on the downstream side and increases on the upstream side as the filter is moved from upstream to downstream. The uplift pressure decreases along the floor, except along the upstream cutoff, with decreases in pervious soil strata depth. The uplift pressure increases all along the floor with increases in depth of downstream cutoff. The exit gradient decreases with increases in depth of downstream cutoff and decreases in pervious soil strata depth.

The mechanics of the limiting‐equilibrium profiles of ripples and dunes are presented. The analysis is based on low sediment transport rates, in which the sediment essentially moves as bedload. The sediment transport rate is taken as proportional to some power, m, of the local velocity. A two‐dimensional flow is assumed in which velocities are computed on the basis of a discontinuous potential flow model and, on the basis of an incompressible, rotational inviscid flow model. A family of curves representing the relationship between the limiting steepness of bedforms and the relative depth of flow for various values of m is presented. The analytical results are compared with the observed data, and the comparison shows a fair agreement.

A modified traveling screen has been shown to be effective in improving fish survival rates at the Mystic Power Station, Unit 7. The survival rate of flounder was nearly 100%, while other species also achieved good survival rates. Continuous operation of the screen during peak abundance periods should provide adequate protection for key species. The modified screens can be inexpensively backfitted to existing intakes, often without plant shutdown.