USGS Water-Year Summary for Site 07381600

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	Available Parameters
	00060 Discharge(Mean)
	00065 Gage height(Mean)

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Water year 2024: 2024-10-01 to 2025-09-30

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USGS Water-Year Summary 2024

07381600 Lower Atchafalaya River at Morgan City, LA

LOCATION - Lat 29°41'33.4", long 91°12'42.6" referenced to North American Datum of 1927, St. Mary Parish, LA, Hydrologic Unit 08080101, at Southern Pacific Transportation Co. railroad bridge, 0.3 miles dowstream from State Highway 90, 0.3 miles upstream from Bayou Boeuf, and 1.0 mile southwest of Morgan City High School. Prior to November 6, 1996 gage located on downstream side of bridge pier cap on U.S. Highway 90.

DRAINAGE AREA - Indeterminate.

REVISIONS HISTORY -

Parameter codes 80154 (suspended sediment concentration, mg/L), 80155 (suspended sediment discharge, tons/day), and 70331 (suspended sediment sieve diameter percent <0.0625 mm) were revised in November 2018, as described in USGS SIR 2018-5147 (https://pubs.er.usgs.gov/publication/sir20185147) for the period Oct. 10, 1989 to February 10, 2015.

SURFACE-WATER RECORDS

PERIOD OF RECORD -
April 1973 to September 1975 (discharge measurements only); October 1976 to September 1994, October 1996 to September 1997 (gage height and discharge measurements only), October 1994 to September 1996, October 1997 to September 2015, October 2015 to current year(unit values only).

Intermittent gage height and discharge collected from 1905 to December 1975.
Data collected from 1927 to December 1975 are available in reports by the Corps of Engineers, New Orleans District and the National Weather Service.

GAGE -
Water-stage recorder and acoustic velocity meter.
Datum of gage is 0.45 ft below NAVD 88. Prior to October 1, 2000, datum of gage was NGVD 29. Prior to November 8, 1996, at site 1,200 ft upstream at same datum. Prior to October 1984 at datum 0.34 ft higher. Prior to July 1983 at datum 0.17 ft higher. Prior to October 1981 datum was NGVD 1929.

REMARKS - Records good. Site affected by tide at all stages. Satellite telemetry at station.

Positive and negative flows at this site are defined by direction and are specified to be parallel to the channel at the gage location. The Positive flow direction is South-southeast.

Streamflow at this site is affected significantly by astronomical tides. Astronomical tides cause significant cycles of approximately 24.84 hours at this site. Because a different portion of the 24.84 hour tidal cycle is averaged in successive daily (24-hour) computations, a systematic secondary oscillation, unrelated to basin hydrology and having a period of about two weeks may be apparent in daily data published from October 1992 to September 2015.

EXTREMES OUTSIDE PERIOD OF RECORD - Flood of May 28, 1973, reached a gage height of 10.53 ft, from incomplete record. Maximum discharge observed during flood of June 8, 1927 was 741,000 ft³/s; minimum gage height , -5.44 ft, Aug 25, 1926 (affected by storm). All data from records of Corps of Engineers, New Orleans District.

EXTREMES FOR PERIOD OF RECORD - Maximum recorded discharge, 512,000 ft³/s, May 29, 2011; maximum gage height, 10.33ft, May 29, 2011 and Jul 13, 2019 during Hurricane Barry; maximum negative discharge, -151,000 ft³/s, Oct 3, 2003; minimum gage height, -0.94 ft, Nov 29, 1976. Extremes may have been exceeded during period of missing record due to Hurricane Andrew in 1992.

WATER-QUALITY RECORDS

PERIOD OF RECORD - Water years 1959, 1973 to current year.

PERIOD OF DAILY RECORD - WATER TEMPERATURE: October 1976 to September 1984, May 1990 to September 1992, December 2014 to current year.
SPECIFIC CONDUCTANCE: October 1978 to September 1981, December 2014 to current year.
pH: December 2014 to current year.
DISSOLVED OXYGEN: December 2014 to current year.
TURBIDITY: December 2014 to current year.
NITRATE: December 2014 to current year.
CHLORIDE-5 FT DEPTH: October 1974 to September 1984, May 1990 to September 1992. CHLORIDE-25 FT DEPTH: October 1980 to September 1984, December 1990 to January 1992. CHLORIDE-45 FT DEPTH: October 1980 to September 1984, December 1990 to January 1992.

INSTRUMENTATION - Water-quality monitor collecting temperature, specific conductance, pH, dissolved oxygen, and turbidity. A second monitor is collecting nitrate.

EXTREMES FOR PERIOD OF DAILY RECORD -

WATER TEMPERATURE: Maximum, 33.0°C Aug. 12, 2023; minimum, 4.0°C Feb. 9-11, 1978.
SPECIFIC CONDUCTANCE: Maximum,622 microsiemens/cm Jan. 21, 1981; minimum, 169 microsiemens/cm Mar. 25, 2016 and Jan. 28 2021.
pH: Maximum, 8.6 standard units, Sep.12, 2019; minimum, 6.8 standard units, multiple occurrences.
DISSOLVED OXYGEN: Maximum, 12.5 mg/L, Jan. 27-29, 2018; minimum, 2.4 mg/L, Jul. 22, 2019.
TURBIDITY: Maximum, 315 Formazin Nephelometric Unit(FNU), Mar. 1, 2018; minimum, 9.0 FNU, Sep. 25, 28, 2023..
NITRATE: Maximum, 2.63 mg/L-N, Jul. 5, 2018; minimum, 0.19 mg/L-N, Oct. 27, 2020.
CHLORIDE-5 FT DEPTH: Maximum, 160 mg/L Jun. 14-16, 1977; minimum, 9.7 mg/L May 15, 1991.
CHLORIDE-25 FT DEPTH: Maximum, 120 mg/L Nov. 5, 1981; minimum, 16 mg/L Dec. 26, 29, 1982, many days during January and February 14, 1983.
CHLORIDE-45 FT DEPTH: Maximum, 130 mg/L Dec. 9, 1981; minimum, 14 mg/L Jan. 26, Mar. 1, and May 27, 1983.