RBF_Cover (for eps) - National Water Research Institute

FEET
1,000
900
800
700
600
VERTICAL SCALE GREATLY EXAGGERATED
DATUM IS SEA LEVEL
Modified from Gann and others, 1973
0 1 2 MILES
Figure 2. Glacial valley-fill aquifer overlain by fine grained sediments in the Great Miami River Valley, Ohio
(from Miller and Appel, 1997).
German researchers experimented with excavating a “window” by dredging accumulated
sediment. While the measure increased RBF efficiency, it was considered temporary, lasting only
weeks before silting over (Schubert, 2000). Rivers whose flow has been altered for flood control
and navigation improvement, such as the Ohio River, are particularly prone to clogging. Steep
gradients and floodwaters that may have scoured the riverbed in the past have been eliminated.
Wells or specially designed tunnels used to extract groundwater and bank filtrate must also be
properly located to maximize system efficiency. Rivers and streams that occur with the thumbprint
of the most recent continental glacial period in the United States (e.g., Wisconsin ice age) have
a similar terraced profile. The unaltered modern river channel carries normal stage flows within
the primary terrace. This terrace corresponds to a 100-year flood plain. Where significantly altered
for flood control or navigation, the river may now have inundated the primary terrace extending
from bank to bank up to the secondary terrace. The secondary terrace extends outward to the
500-year flood plain. This channel was cut into the bedrock by glacially fed rivers. The rivers were
large braided streams laden with sand and gravel. As the glacial outwash diminished, the scour
channels filled with sand and gravel to become aquifers. The tertiary terrace is the remnant of
peak stage flooding and its resultant scouring into the bedrock. Relatively thin and finer grained
sediments were deposited as the flood stage fell (see Figure 2). These sediments may have formed
local, relatively less-productive aquifers that are not connected to the modern river channel. The
secondary terrace is the most productive place to locate RBF wells (e.g., out of main navigation,
interconnected to the river, relatively thicker aquifer, greater potential for effective filtration).
Potential RBF Regions
Grand River
B
0 1 2 KILOMETERS
The greatest potential for RBF — and, in fact, where RBF has been implemented — in the United
States is in the Midwestern states. Figure 3 shows the location of mid- to large-sized communities
in the United States that are located along rivers and on alluvial aquifers. Due to site conditions,
RBF is a viable water supply option for many, but not all, communities.
Midwest stream-valley aquifers in Midwestern states west of the Mississippi River are important
sources of water for communities and industries (Figure 4). These aquifers are unconsolidated sand
and gravel deposits that are thicker, greater in extent, and more productive in the major river
valleys of the region. The stream-valley aquifers are unconfined and in direct connection to adjacent
streams and rivers. Average yields from wells range from 100 to 1,000 gallons per minute, with some
wells yielding over 3,000 gallons per minute (Olcott, 1992). RBF opportunities may be available
Buried Valley
B
EXPLANATION
Clay, silt, and fine-grained sand
Coarse-grained sand and gravel
Sand, gravel, and boulders
Till
Bedrock
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