Journal of Water Resources Planning and Management

Rainfalls during summer season are a major cause of sporadic nonlinear transient drops in daily municipal water consumption. The nonhomogeneous, nonlinear effects induced by rainfall interventions on water use complicate time series model identification and estimation. An iterative computer algorithm, that employs a model‐switching transfer function, is proposed for sequential estimation of the transient drops in the water consumption, so that they can be removed from the time‐series data. Existing time series analysis techniques, which are based on homogeneous, covariance stationary assumptions are not directly applicable, since the water‐use time series never reaches statistical equilibrium. The practical data transformation procedure introduced in this paper is useful for achieving approximately homogeneous and stationary time series prior to model identification and estimation of rainfall intervention effects. The resulting empirical model is a transfer function of intervention time, number of uninterrupted raining days, a moving average of maximum daily temperatures, and a moving average of the most recent water‐use observations. This rainfall intervention model can also be used for online prediction of temporal changes in daily water consumption of a city, given rainfall forecasts. An example is included to illustrate the applicability of this approach, using a record of municipal water use.

A generalized model for simulation of surface water management under a prior appropriation water rights system was recently developed and applied to a major river basin in Texas. The water rights analysis model provides capabilities for evaluating institutional as well as hydrologic water availability. The case study provides a perspective on key considerations in water rights modeling and analysis. A river basin should be viewed as an integrated system. Water available to a particular water management entity depends upon the impacts of other water users in the basin. Increases in reservoir yield achieved by system operations should be properly reflected in water rights. Assigning priorities by appropriation date versus type of use and assigning priorities to refilling storage capacity are two other issues which are illustrative of the complexities of administering and modeling water rights.

The water quality of Lake Rotorua has deteriorated since the 1960s because of excessive phytoplankton growths caused by increased inputs of phosphorus and nitrogen from the Rotorua city sewage treatment plant. Removal of phosphorus alone may produce no measurable improvement in lake condition unless it can be made the limiting nutrient. Even then, this may take a number of years, because of recycling of phosphorus already in the lake system. Removal of nitrogen alone may reduce phytoplankton growth, in the short term (say 5–10 yr) but is not recommended because the algal community may become dominated by heterocystous blue‐green algae, which can meet their nitrogen requirements by fixing dissolved molecular nitrogen and form dense unsightly assemblages. Thus, removal of both nitrogen and phosphorus is recommended. A suggested aim is to restore the lake condition to that which prevailed prior to the 1960s, before widespread public concern about phytoplankton growths developed. The scientific view is that this lake condition is achievable and will reduce the frequency and magnitude of nuisance algal blooms, maintain reasonable water appearance and clarity for recreational purposes, minimize periods of deoxygenation, and reduce internal nutrient inputs. Removal of all sewage effluent from the catchment is expected to achieve the nutrient load reduction that is required. Any sewage discharge increases the risk that the lake condition will be unsatisfactory, but this risk is probably low if the sewage inputs are less then 3 tonnes (t) of phosphorus and 30 t of nitrogen per year.

A mixed‐layer thermal stratification model was calibrated for Woods Lake, a shallow acidic transparent lake located in the Adirondack region of New York, for most of the non‐ice‐cover period of 1985. The model was also used to simulate the stratification regime of the lake for the following year, in which environmental conditions were similar to 1985. For both years the model adequately depicted those stratification features previously identified as sensitive to acidification‐induced increases in transparency, including the thickness of the hypolimnion, the temperature of the hypolimnion, and the duration of stratification. Thus the model may facilitate assessments of the impact of acidification on the thermal characteristics of lakes. Model sensitivity analyses indicate that shallow lakes lose continuous summer stratification if they experience the increases in light penetration reportedly associated with acidification. Further, it was found that accurate specification of light attenuation coefficients and lake bathymetry were critical to the effective application of a stratification model to transparent shallow lakes.

PILOTE is a computer program that attempts to reproduce decisions of expert operators in scheduling outlet pumps at a water treatment plant near Paris, France. The program integrates both mathematical models and heuristics, i.e., rulesof‐ thumb used by operators to select configurations of outlet pumps. The models include statistical procedures for predicting hourly water consumption and a hydraulic simulation for estimating hour‐by‐hour elevation changes at regulating reservoirs and at the elevated reservoir receiving the, pumped flows. The heuristics used by operators are based on factors related to water quantity and quality and to operation and maintenance costs. An evaluation of the program showed that the statistical forecasting procedures performed well, but the simulation model consistently overestimated the volumes pumped. The heuristics included in the program accurately represented rules used by expert operators, except for rules used to rank‐order alternative pumping strategies. The evaluation provided an agenda of research for refining PILOTE so that it can be used routinely.

A branch‐and‐bound enumeration procedure improves the search for an optimal floodplain‐management plan. The procedure considers all combinations of expert‐defined alternative measures. However, through bounding, it eliminates inferior combinations without exhaustive detailed evaluation. In cases for which detailed evaluation is required, we propose using Hydrologic Engineering Center (HEC) system‐simulation, economic‐analysis, and data‐management software. We demonstrate the procedure with an example.

A new approach to solve the problem of designing an aqueduct system in areas of uniform terrain slope is developed. The approach is based on the premise that, apart from the amount of water to be allocated, the location of the elements of an aqueduct system is a variable to be optimized for a minimum cost design. Based on the geographical distribution of the users and the individual demands, a function of demand is established to determine the optimal number of laterals. For each number of laterals, and using dynamic programming, the leastcost layout of the aqueduct system is determined. Then the overall minimum cost solution is determined. Simulation studies of hypothetical cases show that significant savings can be accrued to interest groups financing aqueduct systems through the use of mathematical optimization techniques, and that the least‐cost design depends on the spatial distribution of demand for water.

Rapid economic development in the member states of the Gulf Cooperation Council has led to major hydrologic stresses being laid on the aquifers underlying most of the Arabian Peninsula. These aquifers presently constitute the major local resource and, to a significant degree, they are shared across international boundaries. The “Basic Law” of the GCC provides necessary and sufficient rules for the creation of an international framework to manage these shared groundwater resources.

With increasing demands for water, increasing costs for electrical energy, and often stagnant budgets, water utilities must begin to investigate alternative pumping policies that achieve cost savings while not sacrificing system performance. A study was performed for the city of Raleigh, North Carolina, to determine efficient raw water pumping policies to take advantage of existing storage and newly available time‐of‐use power rates. The problem was formulated as a mixed‐integer linear‐programming (MILP) model. Binary integer variables are used to model commercial demand charges, which are once‐per‐billing period assessments on the maximum on‐ and off‐peak electrical demands. Other costs to be minimized include commercial energy charges, as well as standby generator costs to avoid on‐peak commercial power use. Constraints include satisfaction of water demands, minimum and maximum reservoir levels, minimum and maximum pump run times, and other constraints necessary to ensure feasibility. The model is now being used by the city to achieve substantial savings.

Urban peak flows in metropolitan areas increase with urbanization. Demands for water supply, hydropower, and navigation, among other purposes, are also increased. This creates a complex water system problem that requires rational water use. A hydrologic‐hydrodynamic model was developed in order to simulate a river network system with hydraulic structures in an urban watershed. The hydrologic module was assembled with algorithms for the most important components of the hydrologic cycle in the basin, using six parameters. The hydrodynamic module solves the Saint Venant equations through an implicit forward finite difference scheme. The model developed was applied to simulate floods in the metropolitan region of Sao Paulo, which is the largest industrial complex in Latin America with 12,000,000 inhabitants.