Analyzing the Effects of Navigation Structures Edward Brauer, P.E. Applied River Engineering Center U.S. Army Corps of Engineers – St. Louis District

Location  Middle Mississippi River (MMR)  Primarily examined data from gages at St. Louis & Chester From USGS (2009)Examination of Direct Discharge Measurement Data and Historic Daily Data for Selected Gages on the Middle Mississippi River,

Daily Data at St. Louis, Missouri, since 1861

USGS USACE

What’s the difference? USGS  One small Price meter  Torpedo- shaped weights up to 300 lbs  Manual meter revolution counting  Does not standardize length of time of meter spin at each velocity station (time usually <60 seconds  Measures from fixed structures (Bridges)  Velocity Stations every 50 feet on discharge range  Two velocity observations at 0.2 and 0.8 the depth at each station (average was used as mean velocity)  Relies on heavy torpedo weight on meter cable to obtain soundings USACE  Two large Price meters  Uses flatiron-shaped weights up to 150 lbs  Uses Veedol electrical counter connected to each meter  Time of Spin at each station is 300 seconds  Measures from moveable structures (boats, launches, barges)  Velocity stations every 100 feet on discharge range  One velocity observation at each station at 0.6 depth. Observation used as mean velocity  Uses lead line thrown by leadsman to obtain soundings

Comparative Discharge Measurements St. Louis Overestimation of USACE discharges Max Discharge 604,000 cfs

Conclusions of USACE/USGS Comparative Discharge Studies 1945, 1949 and 1952 “In view of the fact that the physical reduction in floodway capacity, after flood control projects were established and regulating works constructed, was practically negligible and in view of the fact that the U.S.G.S used modern and improved equipment to measure stream flow and that there would be a natural tendency towards improvement of method with the acquisition of experience it is believed that the U.S.G.S. discharge measurements more nearly represent that actual amount of stream flow. Therefore, the reduction in floodway capacity was not an actual physical reduction but an apparent reduction caused by a discrepancy in the accuracy of measuring streamflow by older methods and equipment.” In general the USACE discharge appeared excessively high - exceed the U.S.G.S. discharges by varying percentages up to about 22 percent USACE equipment was to some extent obsolete, and better equipment would have brought about a closer agreement with U.S.G.S. Initial measurements on days that concurrent discharge measurements were taken the average difference between U.S.G.S. and U.S.A.C.E was 10.5% It was found that lateral motion tends to increase the meter spin over that which would be registered by water velocity alone and, therefore is one of the causes of the larger USACE results - When emphasis was placed on reducing lateral movement of boat, difference was reduced to less than 3%.

Daily Data at St. Louis, Missouri, since 1861 From USGS (2009)Examination of Direct Discharge Measurement Data and Historic Daily Data for Selected Gages on the Middle Mississippi River,

Examines Incorrect Hypothesis: Does Not Compare Corps and USGS Data

What if you just look at the 77 years of homogeneous data?

** From Watson C, Biedenharn D (2010) Specific Gage Analyses of Stage Trends on The Middle Mississippi River

Stage-Discharge Relation (Discharge Measurements) St. Louis, Missouri From USGS (2009)Examination of Direct Discharge Measurement Data and Historic Daily Data for Selected Gages on the Middle Mississippi River,

Stage from Ratings St. Louis, Missouri From USGS (2009)Examination of Direct Discharge Measurement Data and Historic Daily Data for Selected Gages on the Middle Mississippi River,

St. Louis, Missouri 3,356 measurements Stage-Discharge Relation (Rating) From USGS (2009)Examination of Direct Discharge Measurement Data and Historic Daily Data for Selected Gages on the Middle Mississippi River,

Summary of Recent Studies by USGS (and Watson/Biedenharn)  Since USGS began operation of gages:  Stage is decreasing for a given discharge at St. Louis for flows less than bank-full, due to wing dikes and reduced sediment flux  Stage is decreasing for a given discharge at Chester for flows less than 2/3 bank- full, due to combined action of wing dikes and reduced sediment flux, and in- filling of Horse Island Chute overflow  Stage has increased for a given discharge for flows greater than bank-full at both streamgages, primarily due to levees on floodplains.  Measurement methods, equipment, and location must be consistent for a valid comparison of data with time  Floods have a substantial effect on trends in measurements and daily data From USGS (2009)Examination of Direct Discharge Measurement Data and Historic Daily Data for Selected Gages on the Middle Mississippi River,

How do USGS, Watson/Biedenharn and Pinter studies compare using USGS data? 700,000 cfs 500,000 cfs 400,000 cfs 300,000 cfs 200,000 cfs

** From Watson C, Biedenharn D (2010) Specific Gage Analyses of Stage Trends on The Middle Mississippi River 2’

Factors Affecting Stage & Discharge  Natural Factors:  Water Temperature Cold water-> higher Q for given stage  Seasonal variations in vegetation thickness Thicker vegetation at end of growing season-> lower Q for given stage  Timing of measurement Rising limb of hydrograph-> higher Q for given stage  Errors in measurement  “Man –Made Factors  In-channel structures Dikes, bendway weirs, chevrons  Floodplain structures Levees, floodwalls, roadways All must be considered when evaluating changes in stage or discharge with time—Small changes might just as likely be caused by natural phenomena as by human impacts

Research at the Ven Te Chow Hydrosystems Lab (University of Illinois)

Questions? “The Mississippi River will always have its own way; no engineering skill can persuade it to do otherwise...” - Mark Twain in Eruption Eddie Brauer, P.E. reports_physicaleffects.html