Environmental Engineering Reference
In-Depth Information
FIGURE 14.2
Conceptual model of
the stages of geomorphic adjustments
in channel form within a reservoir fol-
lowing dam removal (left). Stages of
channel adjustment are associated
with predictable changes in sediment
erosion and deposition (export) and
cross-sectional channel form (wetted
width; right). In turn, we hypothe-
sized that these physical changes in
process and form should dictate phos-
phorus retention or transport as water
flows through the reservoir reach.
Particulate phosphorus export should
be tightly tied to sediment export, and
the degree of sediment
0
0
A
BCDEF
ABCDEF
Stage
Process
Channel form
A
P removal
Reservoir
B
Dewatering
Reservoir
C
Incision
Narrow, deep
water contact
should affect dissolved inorganic
phosphorus removal from the water
column; i.e. phosphorus retention.
(Modified from
Doyle et al. 2003b
and
Stanley and Doyle 2002.)
D
Degradation, mass wasting
Wider, shallower
E
Aggradation, widening
Wide, shallow
F
Quasi-equilibrium
Complex, vegetated
A
B
C
D
E
F
can safely ignore some pools and fluxes if they are small without losing track of the larger
picture of the budget. Put more generally, stepping back to look at the big picture leads us
to ask the general question, how important is the process or phenomenon being studied?
When we began our work, there was already a rich literature on the effects of dams on riv-
ers, but the vast majority of these studies dealt with great huge dams, such as those that
populate virtually all the rivers in the western United States. Yet dams in the more topo-
graphically challenged Midwest tend to be small structures, and these lesser dams and their
reservoirs have attracted little attention from aquatic researchers. This led me to begin to try
to figure out just how many dams there were in Wisconsin, where they were, how big they
were, and whether dam removal was affecting the population of dams in the state.
One of the first things I learned in answering this question was that the abundance of
what I now think of as “little dinky dams”—that is, small structures in small and midsized
rivers—vastly outnumber the larger, grossly conspicuous structures that reach their
extreme types in Hoover, Aswan, and Three Gorges dams. While there is no discounting
