The water-surface elevations on the Inland Waterway Navigation System of the upper Mississippi River are controlled during normal operating conditions by various flow controls at 29 locks and dams. The headwater (naviga tion pool) and tailwater elevations at Lock and Dam No. 7 are controlled by the regulation of 11 tainter gates and 5 roller gates. Discharge ratings for these tainter and roller gates were developed for use in computing discharge through Dam No. 7 and to aid in regulating the navigation pool within its normal operating limits of 639.00 + 0.20 feet (NGVD 1912). Hydraulic-control variables and discharges were measured at the tainter and roller gates and analyzed for this report.
Fifty-two current-meter measurements of discharges that ranged from discharges too low to measure to 12,600 cubic feet per second were made in the forebays of the tainter and roller gates. The measured discharges were used to define flow regimes as a function of static-headwater depth (hl), static-tailwater depth (h3), and vertical height of tainter or roller gate opening (hg). Submerged-orifice flow is the predominant flow regime at Lock and Dam No. 7.
Twenty-four discharge measurements were used to develop submerged-orifice discharge coefficient relations for the 11 tainter gates. Twenty discharge measurements were used to develop a submerged-orifice discharge coeffi cient relation for the five roller gates.
Coefficients of discharge (Cgs) ranged from 0.126 (hg = 1 foot) to 1.089 (hg = 10 feet) for tainter gates and from 0.050 (hg = 1 foot) to 0.302 (hg = 14 feet) for roller gates. Discharge was measured at three different tainter gates with the gates closed (hg = 0) to evaluate the tainter-gate leakage-discharge relations. No measurable leakage was observed. The result ing equations can be used to compute discharge at Lock and Dam No. 7 for the tainter and roller gates under normal flow conditions. Discharge rating tables for the tainter and roller gates are given with a headwater elevation of 639.00 feet normal pool elevation for selected tailwater elevations and gate openings.
Additional Publication Details
USGS Numbered Series
Discharge ratings for tainter gates and roller gates at Lock and Dam No. 7 on the Mississippi River, La Crescent, Minnesota
Water-Resources Investigations Report
U.S. Geological Survey ;
U.S.G.S. Earth Science Information Center, Open-File Reports Section [distributor],