David H. Marks

A new methodology for modelling break failure patterns in deteriorating water distribution systems: Theory

Abstract Two case studies are presented, where Proportional Hazards and Poisson-type models are applied to predict failure probabilities in deteriorating water pipes. It is shown that breaks follow a nonhomogeneous Markov Process during the early stages of deterioration, that is, the failure probability is a function of time and also depends, among other things, on the number of previous breaks. During the later stages of deterioration a constant, but highly varying among pipes, break rate characterizes the failure pattern. In this latter case breaks could be reasonably approximated as Poisson arrivals. The results help in identifying factors that contribute to increased break rates and provide a high level of detail necessary for understanding failure pattern variability at the individual pipe level. The proposed methodologies are expected to provide a useful quantitative tool for improving maintenance strategies.

Location of health care facilities: An analytical approach

Abstract The problem of health facilities location is explored under a mathematical optimization approach. Several models are developed for the location of a generalized health facility system in a region in a manner that the selected criteria are optimized. Locational criteria are structured as a hierarchy of social, economic and political attributes and defined analytically using economic and utility theory. A planning framework, based on the models developed, is presented to aid the health planner in the formulation of health facility location decisions.

Learning about transdisciplinarity: Where are we? Where have we been? Where should we go?

Scholz, a social scientist and decision theorist interested in theoretical basics, and Marks, a systems engineer with experience in real-world problem solving, offer insights on the epistemology, methodology, organization, societal and professional-practice dimensions of transdisciplinarity. Transdisciplinarity represents a move from science on/about society towards science for/with society. Their detailed recommendations include more work on theory, standards of quality, and creating strong institutional frameworks.

Containing groundwater contamination: Planning models using stochastic programming with recourse

Abstract This paper examines the problem of operating pumping wells in order to contain an area of groundwater contamination when the aquifer properties of the area are uncertain. A stochastic program with simple recourse is formulated, involving a non-convex quadratic objective subject to linear constraints. This problem is solved using an extension to the Finite Generation Algorithm that will find an at least locally optimal solution to a problem involving a non-convex quadratic objective function. A numerical example is presented and analyzed.

Capacity expansion for water resource facilities: a control theoretic algorithm for nonstationary uncertain demands

Abstract Municipal water and waste water investments represent a large and important segment of the expenditures made by local governments. The response of designers to the problem of sizing increments to capacity has been to overbuild in order to assure safe and adequate supplies. A growing body of evidence suggests that the magnitude of overbuilding has been excessive. Earlier research has neglected to model demand growth as uncertain with the possibility of both nonstationary mean and variance. Also, failure to recognize the problem as one of closed loop control has resulted in erroneous modeling efforts. The basic approach in this research is to model using stochastic dynamic programming. The criterion was minimization of expected cost. Excess capacity, the state of the system, increases due to investment decisions. Negative excess capacity implies shortage. As time progresses known, but possibly uncertain demands impinge upon the system. Overall, several highly flexible capacity planning models for nonstationary demands can be formulated, are computationally feasible, and produce excellent approximations to known solutions. However, these models should only be used after sensitivity testing in conjunction with simpler approaches.

A new method for the control of the river Nile

This paper introduces a new stochastic control method, Extended Linear Quadratic Gaussian control, that appears to be particularly promising for the management of complex reservoir configurations such as the River Nile system. The method is introduced by means of a short case study related to the regulation of the Equatorial Lakes in the Nile basin. If the necessary data are available, the method can be easily adapted to the entire Nile system and used to investigate a variety of management issues.

Irrigated agricultural expansion planning in developing countries: Performance vs. resilience vs. reliability

The conflict between performance measured in terms of economic and income redistribution objectives, resilience and reliability of irrigated agricultural expansions in developing countries is investigated via a planning framework consisting of three sequential optimization models. The first model determines the most economic planning alternatives. The second model examines, in terms of an income redistribution criterion, the social attractiveness of each plan. The third model determines resilience and operating rules of the various alternatives. The planning framework is appled for a hypothetical agricultural expansion on the order of 30 000 hectares based on data from the Nile Delta in Egypt. The trade-off between system performance, reliability and resilience is derived.

Planning and Design of Agricultural Drainage Systems Under Uncertainty

Abstract Drainage systems are major capital investments for irrigated agriculture. Therefore, the goal is to install drainage systems in a manner that will be most beneficial or “optimal” to the agricultural economy as a whole. The investment decisions for drainage projects are structured in a three level hierarchy. The first level is the project evaluation level, that is the level at which the decision is made if and when an area should be installed with drains. This decision is made on the basis of whether all the project benefits exceed all the costs in some multiobjective measurement. Given that an affirmatice decision is made at the first level, the next level in the process is the planning of the network of collector and main drains. This will include the placement, sizing, and design of the collector drains, pumping stations, and main drains. The third level is the design of the field drains. This is referred to as the field level design process. This process will include decisions on the type, material of, depth, spacing, and installation procedures for lateral field drains. These field drains will empty into the collection network designed in level two. The paper will present a description of the decision process at each level, the activities involved in making these decisions, and the interactions that take place between the various levels of planning. The next section will present mathematical tools that have been developed to aid the decision maker and planners to use the data available at each level most efficiently to allow for “optimal” use of limited resources. The third or field level design decisions are the depth and spacing of the lateral drains. A nonlinear optimization model that incorporates the physics, uncertainty of data, and economics of subsurface drainage will be developed to give the “optimal” spacing and depth of lateral drains. In the second level of planning it is important to define homogeneous areas or districts that will allow for field level analysis to be performed most accurately. A heuristic algorithm for efficiently draining these areas by a collection network will be discussed. This algorithm will allow for feedback between level two and level three and provide a multi-level dynamic drainage planning methodology.

Screening the impacts of municipal service policy changes

Abstract The planning of municipal service delivery systems requires accurate forecasts of demand, and particularly of the effects the quality of service delivery has on demand. A metholology for this problem should meet three criteria, if it is to be useful for municipal planning: it must be low-cost and use generally available data; it must be based on user behavior, so that the effects of policy changes can be correctly attributed; and it must allow testing of the transferability of the results, since this is required for general forecasting use. This paper develops such a methodology, based on econometric analysis of data from a number of service areas within a number of regions, forming a double cross-section. Empirical tests of the methodology were performed for two local government services where the effect of service quality on demand is important: sewer and highway construction, which have been hypothesized to affect the patterns of development within regions; and solid waste collection, where the level of service provided affects how much waste enters the collection system and how much is littered, burned or recycled. The two case studies and other analyses suggest that the methodology is a useful tool for testing whether policy changes have an effect on the demand for service, but not for accurate demand forecasting. Thus, these simple models are relevant for the role of screening the effect of policy changes, but more detailed and localized approaches are necessary for system design.

Computational and Formulation Considerations in Multiobjective Analysis in Water Resource Planning

Abstract The formal representation of large scale water resource planning problems in a multiobiective framework presents difficult conceptual problems in constructing response surfaces as well as computational difficulties in searching for points of good design. This paper first characterizes the nature and complexity of water resource problems and presents a state of the art evaluation of the multiobjective solution techniques employed in their analysis. Then consideration is turned to some important issues in problem formulation i.e. the selection of metrics for evaluating objectives such as environmental concerns and the modeling of physical and social system interaction necessary to predict the outcome of a particular plan in terms of the selected objectives and metrics. Special consideration is given to regional planning problems where modeling efforts to relate economic and social impacts of regional infrastructure development (i.e. transportation and water resources projects) are often on a vastly different scale than models to predict the impact of new projects on the physical environment.