Engineering and Environmental Issues
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Slumping
(Tour
Map symbol 'Sl')
Major slumping occurs regularly on
landscapes formed from the Pierre shale. Strata moves
downslope easily when water from rainfall or melting snow lubricates sediments
lying on hillsides. This threatens roadbed stability and poses a danger for
building sites. The approach to the Missouri River bridge west of Gettysburg
was recently reconstructed at a very high cost after years of temporary repairs.
Sedimentation
(Tour
Map symbol 'Se')
Sedimentation of two of the four Missouri River reservoirs in South Dakota is
becoming a problem . The reservoirs were formed when four hydroelectric
dams (Tour
Map symbol 'Hd') were completed in 1950's and 1960's. Sediment
from erosion-prone soils of central and western South Dakota and northern
Nebraska moves into regional drainage basins and ultimately
into the Missouri River reservoirs. The cumulative reservoir capacity has
been reduced 5-25%. If aggressive erosion controls are not implemeted soon,
flooding again will threaten agricultural land, towns, and cities especially
along the western parts of Lewis and
Clark Lake and Lake Sharpe. Electricity production may be curtailed as well.
Earthquakes
The landforms of the Central and Western are relatively stable. Nevertheless,
since 1872, about 25 earthquakes have been recorded mostly occurring along the
Missouri River and in the southwestern part of the state (see
SD Earthquake Map). Structural damage
was minimal as all of these occurred in rural areas and were measured in the
III-VI magnitude range of the Mercalli Intensity Scale.
Radon
Radon is a colorless, odorless, gas generated from the radioactive decay of
uranium. It has been implicated in the onset of lung cancer. Geological formations
which contain some uranium can generate radon. Several formations occur in central
and western South Dakota which could generate measureable radon levels
(see Potential
for Radon Emission Map). If a concern arises, an environmental
engineer should be consulted to test specific locations for radon levels.