Journal of Hydraulic Engineering

Transient seepage patterns in the west dike station 58+00 of Wallace Dam are studied through a saturated‐unsaturated seepage analysis using a finite element solution technique. Numerical results obtained are presented and compared with field data. Further, a simplified formulation of finite element equations for saturated‐unsaturated analysis is presented which increases computational efficiency considerably.

A general mathematical model is developed for two‐dimensional, unsteady dispersion of a miscible second fluid from time‐dependent, nonuniform, and nonperiodic strip sources in steady, one‐dimensional seepage flow through a homogeneous and isotropic saturated porous medium. Longitudinal and lateral dispersions, radioactive decay, and linear adsorption are considered. In the mathematical analysis, Laplace transform and Fourier analysis techniques are used simultaneously and a general equation is obtained in an integral form for the distribution of concentration. Graphs are presented for two spedal cases of this general model. The solutions can be used to control groundwater contamination and quantitative predictions of spatial and temporal changes in groundwater quality.

Operator and sampling errors in the grid by the number sampling technique for river gravels result in differences between sample and population parameters. Differences between operators occur because of slight differences in stone selection procedure and are independent of sample size. Differences between samples occur because of random errors and these decrease with increasing sample size. Consequently, as sample size increases differences between operators become statistically significant even though physically they remain the same. This is illustrated by data for eight operators. Samples of 30, 60 and 100 show no significant differences but those for 120, 180 and 300 do show significant differences. At small sample sizes, sampling error is large and the sample parameters only approximately define population values. The sample size required to produce a prescribed level of accuracy can be determined from statistical theory and the equations needed are presented here. Where samples larger than 100 stones are used it will be necessary to minimize differences between operators by thorough training. For very large samples and high accuracy one operator must collect all the stones.

Conformal mapping techniques are used to calculate dimensionless flow rates to a collection gallery (a horizontal ditch or porous pipe) for four different combinations of aquifer geometry and boundary conditions. In all cases the lateral aquifer boundaries are two parallel, infinitely long straight lines, and the gallery is a straight line segment that is either parallel or orthogonal to these lateral boundaries. A numerical example is given to illustrate an application of the calculated results.

A nonlinear functional rainfall‐runoff model is applied to an urban watershed (Curotte‐Papineau, Montréal) and the results are compared with those from the ILLUDAS model. Simulations are performed using a 5 minute time interval in order to better define the characteristics of the hydrographs. Particular emphasis is placed on the identification of the most appropriate set of model parameters, namely the memory of the catchment (U) and the order of expansion of the first‐ and second‐order kernels $M_1$ and $M_2\text{.}$ Parameter identification based on calibration results alone can lead to unpredictable verification (prediction) results; while calibration results improve with increasing values of $M_1$ and $M_2\text{,}$ verification results do not exhibit the same consistency. Consequently, a two‐way calibration‐verification analysis is recommended for obtaining the best set of model parameters. Further, results of the nonlinear functional runoff model compare favorably with those of the ILLUDAS model.

A method for calculating the friction factor coefficient in bends is developed. The average water depth in an established section of a channel bend is less than the depth that would be produced in the same place if the channel were straight. A correlation has been found between this loss of depth which is generated by the effect of the curvature and the average flow velocity at the entrance of the channel bend. A logarithmic equation facilitates the calculation of the energy losses in bends. This correlation is based mainly on published flume data for a limited range of flume widths. Also, the magnitude of the shear maxima produced by the curved flow can be predicted by its correlation with the maximum velocity head that occurs at a section where the water surface obtains its minimum depth.

The inclination of flow lines at the exit on the downstream side of a hydraulic structure has been found for a known degree of anisotropy and a given direction for the principal permeability. An analytical procedure is presented to find the exit gradient for steady confined flow in an anisotropic porous medium from known exit gradient of the corresponding fictitious isotropic flow domain. Results have been presented for distribution of exit gradient on the downstream side of a vertical sheet pile embedded in a homogeneous anisotropic porous medium of infinite depth. It is found that the zone vulnerable to piping on the downstream side of a vertical sheet pile is larger for the case of horizontal stratification than for vertical stratification.

A procedure is proposed which uses probability concepts to achieve a consistent and realistic assessment of the probable maximum flood (PMF) and its use in design or evaluation of high‐hazard dams. A PMF computation involves selection of a sequence of meteorologic and hydrologic events. These include the principal storm, antecedent and/or subsequent storms, time and areal distribution of rainfall, loss rates, and the hydrograph determination. Computed maximum headwater levels used in dam design or evaluation depend on assumed initial reservoir levels, operating conditions, and windwave conditions. A review of present practice shows basic agreement on events or conditions to postulate, but significant differences in their magnitude. These differences produce major variations in the relative magnitude of the computed flood. Further, some events are defined in terms which, when applied in different climatic regions, will result in computed floods of varying relative magnitude. The results of studies conducted by the Tennessee Valley Authority to establish a consistent and realistic standard for PMF determination in the Tennessee Valley region are used to illustrate the proposed procedures.