TAKEOFF
BASS SCIENCE
HOW RESERVOIRS AGE
T
WHY IT MIGHT NOT BE YOUR GRANDFATHER’S RESERVOIR ANYMORE
a reservoir that’s heavily silted might
reach a high-water stage faster than in
previous times.
3. Altered flow regime – Another
side effect of siltation is that, as reser-
voirs age, their flow capacity and volume
decrease, which makes them less effi-
cient at generating electricity. Although
not noticeable on the largest reservoirs,
this effect and resulting changes to gen-
eration are noticeable on some of the
smaller ones.
4. Loss of timber and cover – Over
time, any wood in the system such as
standing timber and stumps will
decompose and rot away. Wave and ice
action can also destroy standing timber.
Siltation fills in rocky areas and bottom
contours, reducing the amount of pre-
ferred habitat available to bass.
Effects on the Fishery
The effects of reservoir aging have a
multitude of impacts on the fisheries.
The biggest factor is definitely siltation,
which has great physical impact on the
bottom topography. It causes ditches,
drains and shallow areas to fill in, mak-
ing them less suitable to bass. Areas
that had a steep drop might only taper
gently, and drains leading back to
spawning flats might level out, chang-
ing how bass use them. Siltation also
greatly impacts navigation, rendering
some areas previously accessible to
boats unfishable.
Loss of cover is also a big factor as
bass and baitfish both rely on cover to
proliferate. Typically, the less cover
available, the less prolific the bass
population.
he vast network of dams and
reservoirs in this country is cer-
tainly among the great works of
the 20th century. Beginning in the late
’20s, the construction of dams by local
and federal governments brought
electricity, flood control and unprece-
dented prosperity to folks in desperate
need due to the Great Depression.
From a bass fisherman’s perspec-
tive, these dams provided the sport’s
original home base, and brought bass-
rich waters to areas that previously
offered minimal fishing opportunities.
Many years have passed since the
bulk of those dams were built, and the
reservoirs they impound are getting
long in the tooth. The average age of
dams in the United States is 52 years,
and many are significantly older.
Although the reservoir aging process
is not typically something noticeable to
anglers on a day-to-day scale, under-
standing the process in the context of
regional and multi-year trends will make
you a better angler.
By TJ Maglio
Results of Aging
24
Whether designed for power gener-
ation or flood control, or to provide a
source of drinking water, dams are all
basically the same. They are engi-
neered structures that back up a
stream or river and allow for controlled
release of water. The constant influx of
water, freeze-thaw cycles and recre-
ational uses have definite effects over
time, including:
1. Siltation – If you think of a reser-
voir as a dustpan of sorts, then every
year’s spring runoff is like a new
broomful of dust swept into the sys-
tem. Because of the dam, the runoff
water slows when it hits the reservoir,
causing sediment to drop out, which
over time fills in creeks, ditches and
other areas.
2. Loss of storage capacity – A side
effect of siltation is loss of storage
capacity. From an angler’s perspective,
Stumps and timber remain in many reservoirs, but they degrade over time.
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