Scientists Sound Out Lake Sediment Deposits
Scientists Sound Out Lake Sediment Deposits
Kansas Biological Survey scientists get their share of
stares as they ply the waters of lakes in northeastern
Kansas in their specially equipped pontoon boat. It’s evident that theirs is not a typical afternoon boat ride.
They’re in the midst of a scientific field investigation to
measure, locate, sample and map sediment deposits that
rob a reservoir of its storage space for water and contributes to water quality problems.
Perry is not alone. Since their construction, the more than
300,000 acres of public and private reservoirs and ponds
built in Kansas in the past 100 years have steadily filled
with sediments. No two lakes are alike in either the rate or
pattern of sedimentation. Much depends on the land uses
and the frequency and intensity of storm events in a
lake’s watershed.
The scientists’ findings tell a disheartening, but not unexpected story.
“Ozawkie has lost much of its lake front property,” says
Mark Jakubauskas with the Kansas Biological Survey,
referring to the community on the upper reach of Lake
Perry. “Since Perry Reservoir was built in 1969, the lake’s
surface area in that area has decreased by 1,000 acres.”
Jakubauskas is team leader for the University of Kansas’
Applied Science and Technology for Reservoir Assessment (ASTRA) Initiative. While Lake Perry is not the focus
of the Kansas Biological Survey’s current work (it previously was measured by the U.S.G.S.), it serves as an
example of sedimentation.
Computer display shows lake depth.
The Survey’s work provides some answers. Jakubauskas
and fellow Survey scientists are using state-of-the art,
scientific grade echosounding system to estimate the
sediment thickness and water depth, or bathymetry. They
use two echosounding devices, one operated at 200 kilohertz and another at 50 kilohertz. The higher frequency
essentially measures the depth of the water to the top of
the sediment deposit; the lower frequency penetrates the
sediment and a measures the depth to the original lake
floor. The difference is the sediment thickness.
Mark Jakubauskas, with the Kansas Biological Survey,
describes the measurements made with echosounding
to determine sediment deposits in lakes. He is the team
leader for the University of Kansas’ Applied Science
and Technology for Reservoir Assessment (ASTRA)
Initiative.
Lake Perry’s designers, engineers with the U.S. Army
Corps of Engineers, took sedimentation into account
when they planned the lake with a 100-year life expectancy. Sedimentation has decreased Lake Perry’s conservation storage capacity by 23 percent in 32 years.
Coupled with Global Positioning System (GPS) technology, it’s possible for the Survey’s scientists to systematically navigate the lake to gather data. Echosounding results are compared to simultaneously obtained sediment
core samples. The core samples are classed and analyzed chemically. Images of lake depth created with
acoustic sounding can be superimposed on preimpoundment topographic maps to show changes in a
lake’s bottom. The sediment and lake depth measurement complements reservoir water quality assessment.
Sediment Savvy Helps Chart Watershed Restoration and Protection
Scientific data gathered on Kansas lakes may put a
new twist in the sedimentation tale. The information
will be shared with Watershed Restoration and Protection Strategy (WRAPS) groups, organized above
federal
reservoirs.
Knowledge of the nature
of the sediments and the
land use practices in the
watershed will help them
target resources to prevent sedimentation at its
source, whether it’s field
Echosounding estimates sedierosion or stream bank
ment thickness and water depth. sloughing.
cality of dredging sediment from a small lake used
for public water supply will be evaluated. The dredging project, paid for by earmarked Clean Drinking
Water Fee Funds deposited into the State Water
Plan Fund, will be overseen by the State Conservation Commission. KBS data from the yet-to-be selected lake will give an indication of how much
needs to be removed and a check on how much
was removed.
“The more we know about the lakes and the more
the public understands what is happening, the
greater the likelihood of making a positive difference,” says Mark Jakubauskas. Jakubauskas is
team leader for the University of Kansas’ Applied
Science and Technology for Reservoir Assessment
(ASTRA) Initiative.
WRAPS team members are identifying watershed
needs, setting goals, developing cost effective
strategies and taking action in concert with the
state’s natural resource agencies. Money for all facets will come from the State Water Plan Fund, Environmental Protection Agency 319 Funds administered by the Kansas Department of Health and Environment and local sources.
Statewide, sediment and its tie to public water supply and watershed protection and restoration, is the
focus of the FY 2008 Kansas’ Water Plan Projects
Initiative, developed by the state’s natural resource
agencies, and endorsed by the Kansas Water Authority.
Kansas Biological Survey’s work is just one of the
important aspects. In 2007, the practices and practi-
Using Global Positioning System technology, scientists
systematically navigate the lake to gather data. The red
“line” depicts the boat’s track.
Sedimentation has decreased Lake Perry’s conservation storage capacity by 23 percent since it was
built. The photo at left shows the lake’s extent in 1972; photo at right, the extent in 2003.