Several years ago a Cooperative Agreement was reached among Colorado, Wyoming and Nebraska to provide
adequate flows in the Platte River near Grand Island, NE to
maintain suitable habitat for whooping cranes and other migratory
species during the July and August period. The North Platte
River flows were to come from Lake McConaughy and flow past
the Town of North Platte, NE. However, in 2001 and 2002 when
the necessary flows of 3,000 cfs were released, some flooding
occurred on properties near the town. The Agreement specifically
prohibited releasing flows that would flood properties. Therefore,
the flows were reduced to less than 2000 cfs in accordance
with a directive from the National Weather Service (yes, they
set limits for flood stages).
J.F. Sato & Associates was hired to determine why the
North Platte Channel at North Platte, NE, which historically
carried 16,000 cfs without flooding, could no longer carry
3,000 cfs, and to come up with solutions.
JFSA provided civil engineering services and E&H provided
river mechanics. During a field trip it was discovered that
the problem was extensive aggradation over a 20-mile reach
and invasion of phragmites - a dense, 12-foot-tall reed. A
flood analysis using HEC-RAS was performed. JFSA provided
seven alternatives and three were selected for further study.
Our short-term solution is to construct a series of channels
to intercept flows before they reach the developed area and
to remove phragmites in strategic locations.
Reference: NE Community Foundation, Clayton Derby, 701.426.5072
