Journal of Hydraulic Engineering

The greenhouse effect and resulting increase in the earth's temperature may accelerate the mean sea‐level rise. The rise of sea level relative to land level is already significant at locations of extreme land subsidence such as coastal Louisiana. The state of the art of our understanding of the relative sea‐level rise and its effects on bays and estuaries is reviewed herein. Hydraulic processes, such as tidal range, prism and currents, salinity intrusion, and sedimentation, will be modified. The natural response of bays and estuaries to this rise will include changes in shoreline position, land flooding, and wetlands. The effects on engineering projects and facilities will vary widely according to the design life and site conditions. Management policies for dealing with the problems resulting from the relative sea‐level rise are also addressed.

Ground‐water quality monitoring network design is defined as the selection of sampling sites and (temporal) sampling frequency to determine physical, chemical, and biological properties of ground water. The main approaches to ground‐water quality monitoring network design were identified as hydrogeologic and statistical. The various methods for network design available in the hydrologic literature have been evaluated by considering the spatial scale of the monitoring program, the objective of sampling, data requirements, temporal effects, and range of applicability. Considerable advance has been made over the last two decades that now permit the application of methodical and testable approaches to ground‐water quality monitoring network design, although they mostly serve for preliminary analysis and design. The opinion of the Task Committee on Ground‐Water Quality Monitoring Network Design is that as there continues to be advances in hydrogeochemistry, ground‐water hydrology, and risk and geostatistical analysis, methods for ground‐water quality monitoring network design will be improved and refined, and they will become ever more useful in the important mission of environmental protection.

Buoyant plumes discharged from ocean outfalls are important for dispersing municipal wastewater into the marine environment in many coastal areas, although field studies of operating outfall systems are rare. Here, we report on an extensive field study of the effluent plume from one of the largest wastewater outfalls on the west coast of the United States. This study shows that the dispersion and mixing levels of the plume depend upon the local current speed and ambient density stratification. Under these highly stratified, late‐summer conditions, we find that a combination of temperature, salinity, turbidity, and chlorophyll fluorescence measurements are required to unambiguously identify plume waters. Over the course of these observations, the lcoal current speed at plume depth varied from 0.01 m/s to 0.07 m/s, corresponding to a Froude number Fr range of ${10}^{-3}$ to 0.2. A limited number of dilution estimates are made for the lower Fr case, and these fall in the range 110 to 160, which is within the design range for this type of diffuser. The observed maximum height of rise and wastewater field thickness are in reasonable agreement with laboratory results for zero current speed (Fr = 0). At the higher current speed, turbidity layers originating at the sea floor are observed which result from resuspension of bottom sediments.

Open‐channel flow is examined as a dynamic process. Nonlinear differential equations of flow are linearized, resulting in a transfer function. The resulting function is transcendent, and convenient for use. Evaluation of a step response allows the channel‐transfer function to be written simply but with a separate delay component. The function parameters depend on the distance of the channel cross section. An example of the transient response of a channel and the associated transfer function is given.

Velocity measurements with a fiber‐optic laser‐Doppler anemometer were conducted in steep open‐channel flows over smooth and incompletely rough beds. The channel slopes were changed between 1/500 and 1/25 by steps, and as a result, the Froude number changed from 0.5 to 3. The law of the wall and the distributions of turbulence intensity were examined in more detail. The von $\acute{K}$rmán constant k in the log law was verified to be universally equal to 0.41. On the other hand, the integral constant A in the log law coincided with the usual value of 5.29 in subcritical flows, whereas it decreased with an increase of the bed slope in supercritical flows. This decrease of A was explained by a decrease of the damping factor B in the van Driest's mixing‐length formula. The decrease of B was well correlated with an increase of the friction velocity and the roughness. The streamwise turbulence intensity became smaller in the near‐wall region than the semiempirical universal formula as the friction velocity became larger.

Based on the field experiments conducted on a slope consisting of cow grass (Axonopus Compressus), the study presents the frictional resistance of overland flow on the turfed slope. The rigid stems associted with cow grass deflect the water around themselves, generating a high level of turbulence. The frictional resistance in this study is presented in terms of both the Manning n and the Darcy-Weisbach friction factor f. The results show that both the density of the turf and depth of flow play an important role in affecting the frictional resistance to flow. A high-density grass plot produces high resistance to flow and vice versa. The results also show that the frictional resistance decreases for increasing flow Reynolds number through the grass. Based on analysis of the field data, a value of two-thirds is found to be appropriate for use as the exponent of flow depth in the Manning equation for shallow overland flow.