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Missouri River Intake, R.M. Heskett Electrical Generation Facility

Location:  Mandan, North Dakota
Client:  R.M. Heskett Plant, City of Mandan, Tesoro Refinery

Montana Dakota Utilities (MDU) R.M. Heskett Station’s electrical generative facility’s cooling water supply intake is located north of the City of Mandan along the west side of the Missouri River.  In 1993 a shift in the Missouri River channel resulted in significant changes in the flow pattern along the river’s west bank. This created a shallow side water channel that experienced excessive sediment deposition, which restricted their water supply. This was compounded by drought condtions and extended low releases from Garrison Dam.  During 2003 the Corps of Engineers (COE) determined that signficant reductions in releases were required in order to conserve water within the main stem reservoir system.  A survey of the intake and existing sandbar formations indicated that flows below 14,000 cfs would cut off their water supply.  The forecasted releases were 10,000 to 12,000 cfs.  During 2009 similar low flows of less than 14,000 cfs occurred resulting in reduced flows adjacent to the intake.

MDU retained Houston Engineering in 2003 and again in 2009 to assist in evaluating measures to maintain their water supply and coordinate with the COE and State Engineer to permit the dredging of a channel within the river.  In 2003 approximately 7,000 lineal feet of channel was dredged to a depth of around 3-5 feet below projected minimum water levels.  Approximately 35,000 cubic yards of sediment were removed using a truck and shovel operation.  A shorter 1,600 LF project  removed 12,000 CY in 2009 using a hydraulic dredge.

These efforts required river soundings to define construction limits and to assist in preparing an environmental assessment to achieve COE regulatory compliance.  The COE issued a Letter of Permission (LOP) allowing the project to proceed, after consultation with the USFWS regarding endangered species issues.  A Sovereign Lands permit was also obtained from the North Dakota State Engineer.  Additional reviews included locating the spoil areas to avoid previously indentified cultural resource sites and to discuss water quality issues with the North Dakota Department of Health.