Journal of Water Resources Planning and Management

A methodology for quantifying the variation in pipe failure rates associated with temporal and spatial clustering of water‐main failures is developed. In the first stage a cross‐referencing scheme is used to determine the mean number of failures that occur subsequent to initial pipe breaks and the distribution of numbers of subsequent failures for specified intervals in time and space around these initial breaks. The observed distribution of numbers of subsequent failures is compared with the distribution provided by the Poisson equation based on the mean number of subsequent failures. The second stage uses nonlinear regression to derive the values for coefficients of an equation that captures the changes in the mean number of subsequent failures with variation in the time and space intervals. The equation thus obtained through regression is used to further derive equations for the variation in the failure rate as a function of time or space. The methodology is demonstrated by application to the water‐main pipe failure data base of the city of Winnipeg, Canada.

The surface‐water‐supply index (SWSI) was introduced in Colorado in the early 1980s as a better indicator of water availability in the western United States than is the Palmer drought index. Similar indexes have been subsequently developed in Oregon and Montana. These indexes have found great usefulness in drought monitoring and in triggering specific drought‐related activities by state governments. Two conceptual weaknesses exist in the current SWSIs: (1) Subjective assignment of values to coefficients; and (2) obscured statistical properties of the index. Revisions to overcome these weaknesses include a specific definition of surface‐water‐supply, use of streamflow volume forecasts, and appropriate handling of data to achieve the desired statistical properties of the index. It is also suggested that indexes for individual hydrologic components be developed to provide supporting information to the SWSI. An example of the development of the revised SWSI is given for the Flathead River basin in Montana.

A broad array of computer models has been developed for evaluating reservoir operations. Selecting a modeling and analysis approach for a particular application depends upon the characteristics of the application, the analysis capabilities provided by alternative models, and the background and preferences of the analysts. The objective of the paper is to contribute to ongoing efforts throughout the water‐management community in sorting through the numerous reservoir‐system analysis models and better understanding which methods might be most useful in various types of decision‐support situations. Models are inventoried and compared from a general overview perspective, with an emphasis on practical applications. Considerations in formulating a modeling approach are outlined.

A technique is outlined for assigning uncertainty to the estimation of cumulative probability distribution functions (flow‐duration curves) for river discharge at ungaged sites. Data from existing stage‐discharge gaging stations are used to determine a best‐fit exponent for the adjustment of gaged data to a site within the watershed, and to estimate the uncertainty associated with said adjustment. Average annual discharge is shown to be a good indicator of the required adjustment and uncertainty of cumulative probability distribution functions, especially when applied to mean expected discharge through a water‐development project. The distribution of the actual values around the predicted is log‐normal, with a simple power relationship between discharge and drainage area describing the median values. In this paper, the application is to flow‐duration curves for the addition of hydropower capacity.

A testing procedure to diagnose whether the stochastic dynamic programming (SDP) models for reservoir operations will converge is presented. Theoretically, the stability of SDP can be diagnosed by checking whether a coefficient matrix, connected with the existence and uniqueness of solutions of transition probabilities for the inflows, is linearly independent. The steady‐state SDP model of reservoir operations is guaranteed after the SDP convergence has been approved. If the rank of the coefficient matrix is the same as the number of inflow states, there is precisely one solution for the steady‐state distribution of inflows and SDP convergence will be reached. Otherwise, the SDP model is divergent.

In urbanizing areas, the protection of watersheds draining into potable water reservoirs may present a problem. Growing conflicts are arising between interest in development of land and desire to preserve drinking water supplies from contamination. This paper outlines a strategy designed to preclude development only upon a front buffer zone adjacent to the reservoir itself and lower portions of its tributaries. A wider zone behind (up slope from) the front buffer would be required to have special controls over nonpoint source pollution imposed as a condition of development. This special control buffer zone would provide for reduction in pollution from the runoff that reaches the reservoir from channels and tributaries.