Economic Evaluation of Flow Augmentation:
A Systems Analysis Case Study
JERRY R. ROGERS, Public Health Service Trainee
ROBERT S. GEMMELL, Assistant Professor of Civil Engineering
The Technological Institute
Northwestern University
Evanston, Illinois
INTRODUCTION
The work that is being described here is the outgrowth of a project which was
started in the spring of 1965 by the senior Civil Engineering class, Northwestern
University. Each year the class undertakes a team approach to the planning and
design of a civil engineering project. For 1965 this project was a study of water
management on the Fox River and in the Chain of Lakes region of Northeastern
Illinois, with special emphasis being given to flooding and problems of low summer flows. The latter gives rise to water quality problems both in the Chain of
Lakes and in the Fox River downstream from these lakes.
The Fox River has its headwaters in Waukesha County, Wisconsin, just west of
Milwaukee (Figure 1). It flows almost due south through agricultural land and
enters Illinois just south of Wilmot. Soon after entering Illinois, it passes through
the Chain of Lakes -- specifically Grass, Fox, Nippersink, and Pistakee Lakes --
a series of shallow reservoirs which have been extensively developed for recreational purposes. Outflow from the Chain of Lakes is controlled by McHenry Dam
and its associated upstream channel. The upper portion of the Fox River, some
80 river miles, has a mild slope of approximately one ft per mile. Below McHenry Dam the river continues its predominantly southward course an additional
50 river miles to Aurora, Illinois, whence it flows southwestward for 50 river miles
to join the Illinois River at Ottawa. In this lower portion the average river gradient increases to nearly three ft per mile. This section of river is extensively developed for navigational purposes, and a number of moderate size communities
lie along its course.
The physiography of the Fox River Basin precluded the construction of additional surface storage facilities. Existing storage in the basin consists of the Chain
of Lakes and a number of small impoundments along the length of the river which
serve as navigational aids. This lack of possibility for construction of additional
surface impoundments led to the recommendation of a tunnel whereby flood water
from the Fox River could be diverted from Fox Lake to Lake Michigan. Here,
the water would be stored and returned during the summer and fall months for the
purpose of flow augmentation.
A diversion of 2200 cfs during the passage of the flood was determined to be
the requisite rate needed to alleviate flooding problems in the lakes. Preliminary
estimates of the required diversion flow were made by hand calculation and subsequently verified by computer simulation of the response of Fox Lake and the
diversion facility to the passage of numerous synthesized flood waves. In addition
to providing information about the required rate of diversion of flood waters, the
simulation also permitted evaluation of numerous operating schemes for initiation
and duration of diversion. This is important since it was felt that no amount of
flow augmentation water could be withdrawn from Lake Michigan in excess of that
which was placed into the lake during the passage of the spring flood.
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