FLOOD01647

• County: Statewide
• Title: Optimal Sizing of Urban Flood Control Systems
• Date: 3/1/1974
• Prepared For: US
• Prepared By: COE
• Floodplain - Doc Type: Educational/Technical/Reference Information

simplify their systems to the degree necessary to make use of the more automated
optimization procedures, The belief among planners is that the simplifications
result in not capturing the essence of the system performance and component
interactions.
This paper describes a technique that has been developed and programmed
into an existing Hydrologic Engineering Center (HEC) computer model (6) that
provides an estimate of the "best" size of the individual components of a
complex interrelated system of urban flood-control works while using techniques
of analysis that are very near to the present state-of-the-art in the Corps of
Engineers in hydrologic modeling, cost analysis, and economic damage-frequency
analysis, "Best" is defined as the combination of component sizes that yield
the maximum value of system net benefits while observing performance standard
constraints, if they exist. This capability has been developed so that a system
consisting of up to six detention storage reservoirs, two within or out of basin
diversions, and two pumping facilities can be automatically sized,
The technique that has been developed is designed to be compatible with
present urban flood-control plan formulation methodology, The objective in
its development was the creation of the capability for performing the studies
in the usual fashion but to remove the tedium of searching for the best component
sizes for each system alternative and thus lIncourage the study of a wider range
of system alternatives than might otherwise be considered. Within this framework,
the technique will also permit study of the relative sensitivity of the system
to changes in facility costs, project discount rates, flood-plain land-use controls,
and hydrologic performance standards, so that an array of information can
be easily developed that could be used in formulating a desired management
plan.

PLAN foRMULATION METHODOLOGY

The technique has been developed to be as compatible with current urban
flood-control plan formulation methodology as possible. A brief conceptual review
of the plan formulation and evaluation process in urban flood-control studies
should assist in understanding the development of the technique and its probable
role in planning studies,
Plan formulation begins when public meetings are held and investigations
are initiated to determine the broad social objectives within the study area,
The social objectives primarily serve to assist in defining: (I) The concerns
of the public; (2) concep!s to be used in structuring alternatives; and (3) technical
objectives and criteria that will be used in structuring the technologic components
of management alternatives. For example, such social objectives as alleviating
a specific dangerous flooding situation, providing a regional recreation opportu-
nity, removing the cause of stunted economic growth, and providing a better
community environment would be translated into a range of management
alternatives that would consider the location and severity of flooding, possibilities
of joint site use for specific temporary detention storage and urban recreations,
and appropriate performance standards for components of the systems. The
technical analysis is then performed to define the performance of the alternative
systems and assess their economic, social, and environmental assets and liabilities,
The information developed by these analyses is used in successive refinement

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