Journal of Water Resources Planning and Management

The delta of the Nueces River, Texas, is a low‐lying coastal marsh with dendritic distributaries and flats, infrequently inundated by flood events overbanking from the river. This study examines the feasibility of improving the ecological value of the marsh by creation of diversion works to increase the frequency and duration of marsh inundation. To this end, the morphology and statistical occurrence of flood events in the Nueces were examined using longperiod gage records on the river. A canonical parameterization of flood events was used as input to a numerical hydrodynamic model of the deltaic system, which predicts the time evolution of flow and water level throughout the delta, and includes provision for simulating distributary confluence and difluence, inundation and dewatering of floodplains and flats, and activation of transient channels. The response of the marsh to specified flood events was computed for various alternative physiographies, including existing conditions and candidate combinations of weirs and diversion channels. Coupled with the statistical frequency of occurrence of the specified flood event, the potential ecological value of each diversion alternative was quantitatively established in terms of total inundation period in key segments of the marsh.

A general model for constrained optimum water pricing and capacity expansion is applied to the twin cities of Kitchener‐Waterloo (KW), Ontario. The model identifies the water price and water supply capacity, which maximizes the present value of net economic benefits over a planning horizon. Constraints on the rate of price change and financial cost recovery are included. Results for KW indicate that significant economic benefits can be achieved by jointly optimizing decisions about water pricing and capacity expansion. It is also shown that optimum policies are compatible with the goal of financial cost recovery on the part of the supply authority. The benefits of optimum pricing and capacity expansion are likely to be greatest in water supply systems which exhibit economics of scale or in cities where the rate of population growth is small.

Cleaning and lining a water main is often an economical alternative to installing a parallel main or spending large amounts of money on energy to overcome large head losses due to friction. This paper first presents methods for selecting the length of pipe to be cleaned and lined, and the diameter and length of the parallel pipe to be installed to meet a target head loss. Then, the costs of each approach are compared. In general, the decision to clean and line a main depends mostly on the head loss in the main, at the design flow rate.

For the first 60 yr of the 20th Century, the U.S. policy regarding floods was aimed at flood control. In the past 15 yr, policy has shifted to a goal of flood hazard mitigation. However, flood losses continue to rise and the Congress and others have raised questions about the causes of policy failure. The answer is complicated because flood policy involves 4 currently changing issues, including the shift from federal to local‐state responsibilities; the National Flood Insurance Program; the shift to nonstructural approaches for flood mitigation; and developing programs for emergency assistance. A comprehensive assessment of flood research needs reveals that policy must have a view of efficient use of flood plains, not just loss reduction. The socioeconomic data base is considered inadequate for many policy decisions, and our knowledge of floods is uneven, with much more known in the physical sciences than in the social sciences. Attention to interdisciplinary research involving economists, sociologists, political scientists, and geographers is needed if better policy making and flood hazard mitigation are to be achieved.

Expected annual flood damage for individual residential structures may be estimated using generalized depth‐damage and elevation‐frequency relationships developed by the Federal Insurance Administration (FIA). Damage computation using these data for different locations of the structure in the flood plain show a significant difference between structures located within the 25 yr flood plain and structures located outside. Within the 25 yr flood plain, especially within the 15 yr flood plain, damage for one and two‐story structures with and without basements are exceedingly high: up to ten times greater than those outside. Outside the 25 yr flood plain, expected annual damage decreases gradually with location. These observations have important implications for flood plain management. First, economic feasibility of flood control projects will normally require that a significant number of structures be located within the 25 yr flood plain. Second, removal of structures with high damage potential has the secondary effect of reducing economic feasibility of potential flood control projects. Third, outside the 25 yr flood plain, expected annual damage is relatively insensitive to variations in location, depth‐damage function and frequency. Lastly, estimates of expected annual damage using generalized FIA data is useful in preliminary estimates of the damage reduced.

Two disadvantages of optimization models in water resources planning and management are the simplifications often required to construct the model and user reluctance to rely on optimization models alone. Both of these disadvantages may be overcome by combining a simulation model with an optimization model. In this study, a popular multipurpose, multireservoir system simulation model, HEC‐3, developed by the Hydrologic Engineering Center (HEC) of the Corps of Engineers, is combined with a dynamic programming model. One problem in using discrete differential dynamic programming (DDDP) is determining the initial trajectory. In this project, conventional dynamic programming was used to estimate the initial trajectory, and then a DDDP model was used. Consequently, the optimization model combines conventional dynamic programming and discrete differential dynamic programming to solve the complex problem of operating the California State Water Project's (SWP) Lake Oroville and San Luis Reservoir, given the constraints of the Federal Central Valley Project (CVP) and delta flow requirements. Preliminary results suggest that SWP revenue may be almost doubled by adopting the suggested optimal operation.

An optimization model that determines the minimum cost detention and drainage channel system for a watershed is described. The model determines the location and size of detention basins, the size, type, and number of outlet structures in addition to the design of downstream channel modifications. This new model is based upon dynamic programming for nonserial systems. The model is applied to a watershed for the purpose of illustrating its capabilities.