Those Dammed Lakes - Hydro-Environmental Analysis: Freshwater Environments - page 289

10 Those Dammed Lakes
10.1 RESERVOIRS (DAMMED RIVERS)
As discussed in Chapter 9, G.E. Hutchinson (1903-1991) is considered to be the father of modern
limnology. Among his contributions, he authored the four-volume (with more than 3500 combined
pages) Treatise of Limnology , which is considered to be one of the most comprehensive studies
of limnology in existence. In his 1957 A Treatise on Limnology. Volume 1. Geography, Physics
and Chemistry (Hutchinson 1957), he deined 76 different types of lakes based on their formation.
However, in this over 1000-page long treatise, Hutchinson wrote only two paragraphs about man-
made lakes (as lake type 73, Threlkeld 1990).
While lakes are common and undeniably important, reservoirs (Figure 10.1) are common and
numerous. Reservoirs typically result from impounding some body of water. Reservoirs are most
numerous in regions with few natural lakes, such as the nonglaciated parts of North America (except
Florida), which have the largest numbers of reservoirs (Thornton 1990). There are over 80,000 large
dams listed in the National Inventory of Dams (NID) and an undetermined total number of dams,
probably exceeding 2,500,000 structures nationwide (NRC 1992). Reservoirs are constructed for
some design purpose (recreation, hydropower, water supply, etc.). Therefore, it is the design purpose
and operation that largely impacts the physical, chemical, and biological characteristics of a reser-
voir (Martin and McCutcheon 1999). In this chapter, we will review some of the project types and
structures as they impact the characteristics of reservoirs.
10.2 PROJECT PURPOSES: STORAGE AND POOL LEVEL CONTROL
Reservoirs are constructed for a variety of purposes. The speciic purpose for which a reservoir is
constructed dictates its design and operation, or the principle of “form follows function.”
Of the 82,642 dams in the NID (https://nid.usace.army.mil), by far the most common project
purpose is recreation (Figure 10.2). Other purposes include lood control, ire protection, irriga-
tion, water supply, hydroelectric power, ish and wildlife, tailing control, grade stabilization,
debris control, and navigation. Note that this inventory is limited to signiicant hazard potential
classiication dams and low hazard or undetermined potential classiication dams, which equal
or exceed 25 ft. in height and exceed 15 acre-feet in storage, or equal or exceed 50 acre-feet
storage and exceed 6 ft. in height. Therefore, many of the smaller reservoirs (and ponds) are not
included.
There are a large number of reservoirs, particularly smaller reservoirs, with uncontrolled or
unmanaged releases. That is, the releases are through control structures (standpipes, weir over-
lows, etc.), but the release structure cannot be manipulated to control the releases, such as through
increasing gate openings, etc.
10.2.1 S toraGe
The operation of a reservoir, particularly a large and managed reservoir with a release control, is
related to the manner in which its storage is allocated. Typically, reservoir storage is subdivided into
speciic zones or pools (Wurbs and James 2002) such as those shown in Figure 10.3.
The inactive zone is often not available for use; it is the “dead” zone. Some reservoirs may have
a bottom release structure to aid in draining the reservoir or for water quality purposes. A special