Showing papers in "Journal of Water Resources Planning and Management in 1988"

Water Distribution Reliability: Simulation Methods

Abstract: Following a companion paper on analytical methods, this paper presents simulation as a complementary method for analyzing the reliability of water distribution networks. For this simulation, the distribution system is modeled as a network whose pipes and pumps are subject to failure. Nodes are targeted to receive a given supply at a given head. If this head is not attainable, supply at the node is reduced. Pumps and pipes fail randomly, according to probability distributions with user‐specified parameters. Several reliability measures are estimated with this simulation. Confidence intervals are also supplied for some of these reliability measures. Simulation results are presented for a small network (ten nodes) and a larger network (sixteen nodes). Simulation enables computation of a much broader class of reliability measures than do analytical methods, but it requires considerably more computer time and its results are less easy to generalize. It is therefore recommended that analytical and simulation me...

Water Distribution Reliability: Analytical Methods

Abstract: Probabilistic reliability measures for the performance of water distribution networks are developed and analytical methods for their computation explained. The paper begins with a review of reliability considerations and measures for water supply systems, making use of similar notions in other fields. It classifies reliability analyses according to the level of detail with which the water system is modeled, and then concentrates on methods relevant to networks. Two probabilistic measures, reachability and connectivity, are explored for use in water distribution systems. Two algorithms for their computation are presented, one for series-parallel networks and one for general networks. These measures are computed for two systems, each with ten nodes. Additionally, the probability that a given point receives sufficient supply is proposed for use as a reliability measure. An algorithm is presented for the calculation of this measure, which combines a capacitated network algorithm with a method to efficiently search through network configurations involving multiple link failures. This measure is calculated for the two sample systems.

Modeling distribution-system water quality; dynamic approach

Abstract: Interest is growing in determining the quality variations that exist in drinking water distribution systems. This paper is dedicated to understanding distribution‐system quality issues and to the development of a model that will enhance this understanding. A dynamic algorithm that can be used to predict water quality variations is described in this paper. Determination of the blending of flows from separate sources, tracing of transient concentrations in the system, and establishment of a compliance monitoring system are only a few of the potential uses of such a model. The model has been implemented on a microcomputer and applied to the North Penn Water Authority distribution system, Lansdale, Pennsylvania. It shows good correspondence with observed field data.

Planning Model for Optimal Control of Saltwater Intrusion

Abstract: A planning model is presented for the control of seawater intrusion in regional groundwater systems. The management model is structured as a problem in optimal control. The hydraulic response equations, which are developed from continuity principles, relate the movement of the interface to the magnitude and location of groundwater pumping and recharge. Finite difference methods are used to approximate the solution of the aquifer's response to management strategies. The control problem is solved using: (1) The influence‐coefficient method allied with quadratic programming; and (2) reduced‐gradient methods in conjunction with a quasi‐Newton algorithm. The planning model is applied to the Yun Lin groundwater basin in southwestern Taiwan where excessive pumping has produced declining water levels, localized land subsidence, and saltwater intrusion. The optimal groundwater pumping and recharge schedules for the Peikang area of the basin are presented. The computational efficiency of the algorithms is also disc...

Multicriterion selection of wastewater management alternatives

Abstract: Multicriterion decision‐making (MCDM) techniques are used to analyze a multiobjective wastewater management problem in order to select an appropriate management scheme. A specific case study consisting of 15 alternative management schemes is evaluated with respect to 12 noncommensurable, discrete criteria, using three different MCDM techniques; compromise programming (CP), cooperative game theory (CGT), and ELECTRE I. The case study is the Nogales International Wastewater Management Project, which treats wastewater coming from the twin cities of Nogales, Arizona and Nogales, Sonora, Mexico. The problem is formulated in a multicriterion context in terms of objectives, specifications, criteria, criterion scales, and construction of an evaluation matrix that consists of the alternative versus criteria array. Analyses of the matrix using the MCDM techniques result in selecting the most satisfying alternative in the case of CP and CGT and narrowing the choice to a few non‐dominated alternatives (here, two) in ...

General Water Supply System Simulation Model: WASP

Abstract: WASP is a mass‐balance quasi‐simulation computer package developed to facilitate analysis of the performance of the head works and transfer components of a water supply system under different operating policies and changes to system configuration. Its generality is due to the use of a network linear program (LP) which allows system components to be connected in virtually any configuration. The user defines an operating policy in terms of easily understood rules which guide the network LP when it makes seasonal assignments of water within the water supply system. WASP is based on a network LP to take advantage of computer codes up to 100 times faster than standard LP codes. This paper discusses the principles used to formulate the network LP. It then presents a case study involving a complex urban water supply system to demonstrate the generality of WASP. Finally it reviews the input/output features of WASP which streamline its use.

Multicriterion Stormwater Management Methods

Abstract: Both theory and experience indicate that, while detention basins designed to control peak discharge are effective in controlling peak rates, the basins are ineffective in controlling the degradation of erodible channels downstream of the basin. The increase in runoff volumes that accompanies land development causes greater rates of channel degradation because of the increased duration of high in-bank flow rates. While planning and design procedures are available for peak discharge control, there has been a need for similar methods for the control of channel erosion and water quality. A relationship for making planning estimates of the volume of detention storage required to control channel erosion is provided. A procedure that can be used for design is also provided. Planning and design methods for water quality control through detention time control are also provided. The importance of adopting multicriterion stormwater management policies is emphasized, with the policy recommending control of flooding, channel erosion, and detention time for water quality enhancement.

Operational Guidance During Droughts: Expert System Approach

Abstract: Seattle, Washington, suffered its most extreme drought on record during the summer and fall of 1987. Severe and continuing water use restrictions were required to limit the drought's impact on municipal water supplies, fish populations, and navigation. This paper describes a decision support system used to aid in drought decisions. Its components include an expert system, a linear programming model, database management tools, and computer graphics. The expert system incorporates operator experience and intuition using a rule base developed through interviews with management personnel from the Seattle Water Department. The expert system also integrates the other programming techniques into a single system. A linear programming model determines system yield and optimal operating policies for past hydrologic regimes. Database management and graphics software store and allow the display of over two thousand operating policies to decision‐makers. The system provides user‐friendly support to help decision‐maker...

Adjustment Factors for Flood Damage Curves

Abstract: Estimates are provided for quantifying adjustments to depth–damage tables as a result of flooding events of different types on residential dwellings. The adjustments reflect estimated changes to flood damages due to the availability of flood warning, long durations of flooding, and ice and high velocity flow. Regression analyses are described that examine the degree to which a range of variables, including a resident’s experience with flooding, householder income, floor area of residence, and assessed value of property, can explain the variability of flood damage curves.

Better Than “Optimal” Method for Designing Drainage Systems

Abstract: The Lotus 1‐2‐3 spreadsheet package has been used to develop a stormwater drainage design method which is based on the Florida Department of Transportation's (FDOT) hand tabulation form (FDOT 1987). By using the FDOT procedure, the spreadsheet method allows engineers already familiar with the manual calculation procedure to more easily adapt to the new microcomputer environment. The spreadsheet performs the necessary calculations quickly and easily while not hindering the user with tedious input procedures and confusing algorithms typical of many computer codes. The spreadsheet method also employs a heuristic cost estimation approach which allows the user to find a least cost design. This method has been used to solve a problem previously solved with two dynamic programming algorithms. Since the spreadsheet method does not use a sophisticated optimization algorithm, many simplifying assumptions made in the dynamic programming algorithms are not necessary. The results show that the spreadsheet method was a...

Grid‐Based Application of Runoff Curve Numbers

Abstract: The development and validation of a methodological approach to predicting runoff over large regions is considered. The Soil Conservation Service (SCS) runoff curve number procedure is modified to allow for areal variation of land use and land cover, soils, and rainfall over a regular-gridded network. Ten rainfall events, fro the period 1973–1980, are selected to estimate runoff for the Mahantango Creek Watershed (421 km\ua) in east-central Pennsylvania. The method may be useful in generating a geographic information system database for distributed-components hydrologic models and for water resources management.

Schematic Models for Distribution Systems Design. I: Combination Concept

Abstract: This is the first of two papers dealing with schematic models for water distribution systems. Schematic models for use in preliminary design of water distribution systems are developed by two approaches: (1) A step‐wise combination of elements; and (b) a nonlinear continuum representation of the system as a whole. The objective is to create models that are equivalent to a detailed network model in terms of the computed distributions of heads and flows over the area, yet are much more efficient, and therefore enhance the engineering‐economic analysis. The step‐wise combination method is developed beyond existing procedures to consider more complex arrangements of pipes as well as water withdrawals, which vary along the pipes and with time.

Flood Depth—Damage Curves By Interview Survey

Abstract: Results of interview surveys for potential flood damages are used to develop depth—damage curves for structural and content groupings and alternative residence types. Statistical significance tests are used to collapse 28 structural categories into seven basic groups. The exterior of the residence is demonstrated to not necessarily be a good indicator of the potential flood damage to the contents. Use of average curves are recommended except in the very obvious circumstances of very low and/or very high valued residences.

Nonpoint Source Pollution Monitoring Program Design

Abstract: This paper describes a computer‐aided methodology designed to aid in the determination of water quality and ecological change resulting from nonpoint sources of water pollution. The nonpoint monitoring program design conceptual model developed by the writers involves the following steps: (1) The definition of monitoring program objectives to guide data‐collection efforts; (2) a choice of levels of detail to apply in carrying out the various steps of the procedure; (3) a watershed analysis to identify locations of the potentially most critical pollutant loadings; (4) the development of a monitoring program to detect and verify statistically the source or sources of a nonpoint pollution problem; and (5) prioritization of monitoring tasks with reference to trie program objectives. Spreadsheet software with graphics is used to simplify the watershed analysis. FORTRAN programs are applied to facilitate the design of alternative sampling programs and to prioritize the tasks. A case study example on the Stillagu...

Conflict Resolution in Water Resources: Two 404 General Permits

Abstract: The use of alternative dispute resolution techniques in water resources is demonstrated and experience evaluated against current theory of bargaining and negotiating. Conflicts among environmentalists, developers, and government agencies are well known; they involve planning, constructing, operating, and regulating water resources projects. Two Section 404 permit cases are compared. One in 1980, involves issuing a general permit (GP) for wetland fill on Sanibel Island, Florida. The other, in 1987, involves issuing a GP for hydrocarbon exploration drilling throughout Louisiana and Mississippi. Generally, permits are granted on a case‐by‐case basis, but Corps district engineers may also issue GPs for activities that produce no negative cumulative impacts. In these cases the Corps adopted a revolutionary approach to GPs. Rather than writing the permit in house, the Corps suggested that the parties who conflict over permit applications get together and write the technical specifications for a GP. The Corps to...

Fitting Minima of Flows Via Maximum Likelihood

Abstract: A statistical method for deriving frequency distribution functions of minima of streamflows is presented. An innovative feature of the proposed methodology is that it does not require the specification of a parent distribution for streamflows, i.e., it is distribution free. The only assumption necessary is that the realizations of streamflows be independent, identically distributed random variables. The validity of this assumption is established with a nonparametric test. The main use of the methodology developed herein is in estimating small quantiles of the flow distribution for water supply planning and low‐flow investigations. An example is included to illustrate the applicability of the approach, using a record of annual flows.

Cost-benefit analysis of flood plain zoning

Abstract: The economic yield of a flood-plain zoning program is measured by cost-benefit analysis. The methodology entails the use of a probabilistic hydroeconomic model to evaluate expected flood damages with and without zoning. The application shows that this type of program, albeit cost-effective overall, may be unacceptable for various reasons to the various parties involved.

Risk Analysis of Aquifer Contamination by Brine

Abstract: Underground disposal of liquid wastes poses a danger of groundwater contamination. The prediction of their impacts is subject to many uncertainties. This paper develops and applies a risk analysis model that addresses several of these uncertainties. The model inputs are hydrogeologic parameters, the reliability of waste disposal, and demographic information. The outputs of the model are probability distributions of the number of rural home wells or municipal groundwater well fields that may be contaminated. Contamination is defined as occurring when the concentration for any disposed chemical exceeds its water quality standard. The model is used to analyze the risks posed by annular disposal of oil and gas brines in Ohio. It is found that the economic costs associated with those risks are an order of magnitude smaller than the benefits of the practice.

Metropolitan Water Market Development: Seattle, Washington, 1887–1987

Abstract: In many metropolitan areas it is common for a large central city to sell water to many of its surrounding suburban communities. In the Seattle, Washington metropolitan region, the city (population 494,000) provides water to 34 suburban cities and water districts with a total population of roughly 596,000. The development of this water market has its origins in the geographic pattern of metropolitan population and institutional development, water law, the economies of scale of water production, and the economic scarcity of clean, inexpensive water sources. Management and long‐range planning for such a system are reviewed and the advantages and disadvantages of this market system for Seattle and its customers are discussed. The de facto regionalization of the metropolitan water supply is contrasted with the de jure regionalization of metropolitan Seattle's wastewater system, which is managed jointly by the region's governments.

Objective Rainfall Evaluation in Radar Hydrology

Abstract: A newly developed bivariate statistical analysis is compared to several rainfall analyses, namely the radar univariate analysis, the reciprocal‐distance raingage interpolation model, the Brandes field adjustment procedure, and the “optimum” raingage analysis. A number of statistics are also computed and used to evaluate the results. Several warm‐season storms are examined over the Grand River basin above Cambridge in southern Canada. Based on the selected criteria, the analyzed storms indicate that, in general, most of the techniques in the comparison performed similarly, with the exception of the radar univariate analysis, which is considered unsatisfactory.

Regression Estimates for Topological-Hydrograph Input

Abstract: Physiographic, hydrologic, and rainfall data from 18 small drainage basins in semiarid, central Wyoming were used to calibrate topological, unit-hydrograph models for celerity, the average rate of travel of a flood wave through the basin. The data set consisted of basin characteristics and hydrologic data for the 18 basins and rainfall data for 68 storms. Calibrated values of celerity and peak discharges subsequently were regressed as a function of the basin characteristics and excess rainfall volume. Predicted values obtained in this way can be used as input for estimating hydrographs in ungaged basins. The regression models included ordinary least-squares and seemingly unrelated regression. This latter regression model jointly estimated the celerity and peak discharge. The correlation between residuals of the celerity and peak-discharge regressions was sufficiently large to decrease the variances of estimated univariate-model parameters.

Schematic Models for Distribution Systems Design. II: Continuum Approach

Abstract: This is the second of two papers dealing with the development and use of schematic models for water distribution systems. The first paper covered methods for step-wise combination of elements into equivalent ones. Herein, a different and novel approach, which views the system as a nonlinear horizontal continuum, is proposed. An areally distributed conductance, a function of pipe properties and areal density, is the link between a potential function, which is related to the heads and the flow field. The model can be used to obtain the flow field of an existing system for a prescribed potential, or to optimize the conductance of a planned system for a given distribution of demands and specified boundary conditions. The method is demonstrated by a case study, for the city of Jerusalem, Israel.

Design of Sewage Lagoons Using Stochastic Streamflow Sequences

Abstract: A risk‐based design procedure for hydrograph‐controlled release sewage lagoons is derived. This procedure is based on a stochastic analysis of flood interarrival time, duration, and volume. By modeling streamflow as a Poisson counting process, stochastic sequences consisting of maximum interarrival times and minimum duration are constructed. These sequences are used as the basis for lagoon design by calculating their recurrence intervals based on the joint probability of exceedance of the components of the sequence. Sequences such as those derived here are shown to occur in nature.

Potential Hydroenergy Production by Optimization

Abstract: This paper presents the solution of the very specific problem of potential hydroenergy production in the North Backa hydrosystem (Yugoslavia). The system was designed for supplying water to agricultural areas by pumping water from the River Tisza on the higher elevation and transferring it to the Rivers Cik and Krivaja. An optimization analysis was done for the purpose of examining the possible hydroenergy production aiming at reducing the costs of pumping.

Cisterns for Water Conservation and Flood Control

Abstract: In this paper the potential contribution of privately owned cistern systems to both water conservation and flood control in arid and semi‐arid regions is examined. Although it is demonstrated that, given the current cost of water in the American Southwest, cisterns are not yet a viable water conservation alternative; it is demonstrated that in situations in which water conservation and flood control benefits can be combined, cisterns are a cost effective alternative that should be considered.

Groundwater Contamination Benefit‐Cost Analysis Methodology

Abstract: A procedure for estimating benefits associated with the cleanup of groundwater contamination is proposed. The first step in this procedure is development of a joint probability distribution of contaminant concentration and duration of exposure at a specified location X. A computer model using the turning bands method to generate spatiallyvarying, but correlated hydraulic conductivity fields and a groundwater flow/mass transport computer program to move the contaminant downstream is used to construct the probability distribution. The second step is involved with the formation of a joint incidence fraction distribution of test organism response to various contaminant concentration and duration of exposure levels at the specific location. The sum of the products of the joint probability and incidence fraction distribution values for various contaminant concentration and duration of exposure levels are multiplied by the number of organisms exposed at the specified location in order to estimate benefits result...

Wet Weather Water Quality Modeling

Abstract: An integrated, rainfall‐runoff and runoff‐receiving waterquality modeling protocol was developed to quantify the impact of combined sewer overflow events on in‐stream dissolved oxygen concentration. Modeling assumptions and input data requirements are consistent with intended usage as a planning and management tool. The modeling protocol was successfully calibrated and verified using data collected from several storm events occurring during the summer and fall of 1982. The expected frequency of in‐stream dissolved oxygen violation was determined from the analysis of historical records containing 208 combined sewer overflow events. 42% of these events resulted in minimum dissolved oxygen values below the 4.0 mg/L standard. Sludge deposit resuspension was demonstrated for a monitored high flow event when the in‐stream velocity was computed as 0.689 m/s (2.26 ft/sec).

Spatial Correlation of Hydrologic Time Series

Abstract: A methodology for extracting random components and estimating the relationship between coherent components of hydrologic time series has been presented. The technique has been verified using synthetic data and validated using measured data. The results show that random component statistics are accurately estimated, and the correct relation between pairs of stationary and nonstationary time series are estimated for frequency components whose amplitude significantly exceeds the standard deviation of the random component. Applying the method to measured, nonstationary hydrologic data demonstrated that the technique was able to accurately predict the measured fluctuations in 9 of the 12 years considered. Significant portions of the spectrum of the measured series were found to have characteristics consistent with the existence of a random component. A primary application of the results of this study is to fill in missing data at one location based on measured data at an adjacent location.