Demand Estimation

Demand is required to size water systems to meet some purpose, or establish that the particular system is infeasible.

Note

This entire section is not yet complete - until so done, refer to Demand Estimation.pdf. The content is identical. As the content is moved here obsolete parts will be identified, and newer ideas inserted.

Estimates of demand are used to size water systems to meet some purpose, or establish that the particular system is infeasible.

The purposes can include:

  • Municipal uses (drinking water, fire suppression, commercial use, …)

  • Industrial use (separate from municipal)

  • Agriculture use

  • Waste Assimilation use

  • Navigation uses (outside scope this course)

Water Needs for a City

Consider some generic urban area (cite textbook)

  • Municipal Requirements

  • Large Industrial Requirements

  • Waste Assimilation Requirements

Municipal Requirements

A simple relationship establishes municipal requirements:

\[ V_{required} = P_{t} \times U_{per person}\]

where \(V\) is the volume required, \(P_{t}\) is the population at some moment, \(U\) is the per person usage.

Thus the two components required to estimate demand is how many people have to be supplied, and how much each person uses.

Population Models

GEOMETRIC GROWTH (MATHEMATICAL)

When the growth curve is in the exponential phase

\(P_2 = P_1*e^{K_p(t_2-t_1)}\)

where \(K_p\) is the exponential growth constant

ARITHMETIC GROWTH (MATHEMATICAL)

When the growth curve is roughly a straight line, then

\(P_2 = P_1 + K_A(t_2-t_1)\)

where \(K_A\) is the slope of the growth curve

DECLINING GROWTH (MATHEMATICAL)

When the growth curve approaching the carrying capacity of the region

\(P_2 = P_1 + (P_{sat} - P_1)\cdot(1-e^{K_D(t_2-t_1)})\)

where \(K_D\) is the declining rate constant

Temporal Variation

The demand is not constant, methods to consider the demand variation within some planning interval are available.

Water Demand Variation Tool

Readings

  1. Gupta, R. S. 2017. Hydrology and Hydraulic Systems. Waveland Press, Inc. pp 1-19 http://54.243.252.9/ce-3372-webroot/3-Readings/WaterDemand-Gupta.pdf

  2. Nickerson G. 2008. “Water Distribution Systems” in Land Development Handbook, Ed. S.O. Dewberry, Dewberry Inc., McGraw-Hill http://54.243.252.9/ce-3372-webroot/3-Readings/water-distribution.pdf