OPTIMAL LOCATIONS OF MONITORING STATIONS IN WATER DISTRIBUTIONS SYSTEM

Lee, B.H., and Deininger, R. A., 1992, “OPTIMAL LOCATIONS OF MONITORING STATIONS IN WATER DISTRIBUTIONS SYSTEM,” JOURNAL OF ENVIRONMENTAL ENGINEERING-ASCE, Volume: 118, Issue: 1, Pages: 4-16.

Drinking-water quality should be monitored for public safety. According to the drinking-water regulation, monitor stations need to monitor the sampling frequency and the water-quality parameter. However, specific methods had not been provided for sampling in a distribution system. In this article, a method, how to install monitoring stations in a water network, and a concept of coverage were introduced.

To achieve this method, demand pattern and the flows must be known first. Then, possible locations, called nodes, should be known with the demand. The term ‘covered’ or ‘coverage’ was also used as percentage, which refers to how much demand of the total demand a node covers and which informs the degree of a representative. There is also an assumption that ‘if all the water at the sampled node came from an upstream node, then the water quality of this upstream node would also be known’.

The specific general algorithm is as following.

1. Choose one node.

2. Determine all connected nodes.

3. Calculate water fraction of the flow coming from upstream nodes.

4. In a coverage metrics, the node set to ‘1’ if the value of fraction is above a certain criteria. If it is below the criteria, the node set to zero.

5. As step 2-4, calculate them about all nodes

6. Problem formulation

7. Get result through integer programming

This article also explains that the method can solve multiple scenarios through various examples such as different direction among the node. In result of examples, the author shows the improvements and effectiveness about selecting sampling sites with combining pathway analysis, coverage matrices, and integer programming.

Discussion

This article is interesting because the method provide how to handle pathway when we have to optimize problems relative to road ways or pipes. This is also helpful for me to understand how to solve the third question of our homework. However, although the article provided 2 examples and seemed to simply solve these problems, I think that calculating all the fractions would take longer time if number of nodes increased. If there was a simple method to calculate the fractions, the author should provide the way. If there was not, I would like to study a simple method for estimating the fractions in this article.

Water-resources optimization model for Santa Barbara, California

Nishikawa, T., 1998, “Water-resources optimization model for Santa Barbara, California,” JOURNAL OF WATER RESOURCES PLANNING AND MANAGEMENT-ASCE, Volume: 124, Issue: 5, Pages: 252-263.

In this article, a simulation-optimization model were performed to minimize the cost of water supply, fulfill water demand, and control saline water intrusion from near ocean in Santa Barbara area during a drought. In this model, decision variables were water conveyances from surface and ground water and hydraulic head. Sensitivity of the model was also provided about demand, carryover, head constraints, and capacity constraints.

In detail about a formulation, to fulfill minimizing the water supply cost, a linear programming was employed. The objective is subject to maximum water-supply capacity, maximum and minimum heads along the cost, limits retaining pumping distributions among producing zones, recharge distribution, and water-supply demand constraints. The decision variables were amount of water delivered from surface water, ground water, and Cachuma Reservoir carryover. Additionally, to estimate the heads from pumping pattern, the response coefficient method was employed. MODFLOW method was also used for ground-water flow model.

After select constraints, there were three kinds of scenarios. First, in Base Case which is average monthly releases, the optimization scenarios optimally reached the minimum cost with satisfying all constraints. It means that cheapest water and inland wells would be used as much as possible. In other approaches which were current and prosed monthly Gibralter distribution, the result were not better but it showed that water distribution timing is really important to minimize the cost. In addition, through sensitivity analysis we can also know that additional saving will occur if seawater intrusion is acceptable.

Discussion : This article is interesting because it shows that how to use a linear optimization method for real problems and how to set complex variables and constraints in the linear approach. However, though components of this model were quite reasonable, it would be better if there were detailed constraints and variables such as maintenance or economic trend. In case of allowance of seawater intrusion, there should be environmental impact. For further study, I would like to add additional components mentioned above or other substitutions in this study.