Selection and Design of Channel Rehabilitation Methods
situation does not necessarily ensure it will be effective in another. Some of the more common types of
grade control structures used in a variety of situations are discussed in the following sections. For more
information on various structure designs, the reader is referred to Neilson et al. (1991), which provides
a comprehensive international literature review on grade control structures with an annotated bibliography.
6.2.1.1 Simple Bed Control Structures
Perhaps the simplest form of a grade control structure consists of dumping rock, concrete rubble,
or some other locally available non-erodible material across the channel to form a hard point. These
structures are often referred to as rock sills, or bed sills. These type of structures are generally most
effective in small stream applications and where the drop heights are generally less than about two to three
3 feet. A series of rock sills, each creating a head loss of about two feet was used successfully on the
Gering Drain in Nebraska (Stufft, 1965). The design concept presented by Whitaker and Jaggi (1986) for
stabilizing the streambed with a series of rock sills is shown in Figure 6.1. The sills in Figure 6.1 are classic
bed control structures which are simply acting as hard points to resist the erosion of the streambed.
(a)
ORIGINAL BED
STABLE CHANNEL
SLOPE
(b)
BLOCK SILLS
STABLE REACH
(c)
STABLE CHANNEL
SLOPE
Figure 6.1
Channel Stabilization with Rock Sills (adapted from
Whitaker and Jaggi, 1986)
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