Cooper (Chapman) Lake Water Level Today - 435.96 ft, 73.7% Full

Sulphur River · Texas - updated daily from official gauges

Western Reservoir Conditions·Daily·No. 47·Tuesday, September 8, 2026·Latest reading September 8, 2026

• Cooper (Chapman) Lake is 73.7% full - moderate on this site's capacity scale - as of September 8, 2026. Surface elevation 435.96 feet, storage 190,712 acre-feet (capacity basis 258,723 acre-feet), per Texas Water Development Board data.
• That elevation is its lowest September reading since 2022, and 13.94 feet above its record low of 422.02 ft (December 28, 2006), in a daily record going back to October 1, 2000 (TWDB's period of record for this reservoir).
• Storage is 94% of the September 8 average across 26 years of record.
• Cooper (Chapman) Lake is falling: elevation changed -0.28 ft over the past week, -1.32 ft over the past month, and -2.51 ft over the past year, per Texas Water Development Board data.

Cooper (Chapman) Lake has fallen 2.51 feet in twelve months, and now sits 13.94 feet above its record low.

Cooper (Chapman) Lake vs its record low

In the daily record used by this site (going back to October 1, 2000 (TWDB's period of record for this reservoir)), Cooper (Chapman) Lake's lowest surface elevation was 422.02 feet on December 28, 2006, when storage was 41,647 acre-feet. As of September 8, 2026, Cooper (Chapman) Lake is at 435.96 feet - 13.94 feet above that record. The record high in the same series was 448.51 ft on March 2, 2018.

Cooper (Chapman) Lake storage in context

Cooper (Chapman) Lake water level, past 12 months

73.7% full at the latest reading - across the past 12 months it ranged from 68.5% (February 13, 2026) to 90.1% (June 25, 2026). Percent full is storage against the 258,723-acre-foot capacity basis, not a share of the elevation plotted above.

Cooper (Chapman) Lake elevation, full record

73.7% full at the latest reading - across the storage record since October 2, 1993 it ranged from 16.1% (December 28, 2006) to 105.4% (April 10, 2003). Percent full is storage against the 258,723-acre-foot capacity basis, not a share of the elevation plotted above. Every percentage here is measured against today's capacity basis; a reservoir's surveyed capacity changes as sediment accumulates behind the dam, so early-record percentages are indicative rather than exact.

Last 14 daily readings

Frequently asked questions

What is the water level of Cooper (Chapman) Lake today?

As of September 8, 2026, Cooper (Chapman) Lake's surface elevation is 435.96 feet, with 190,712 acre-feet in storage - 73.7% of the 258,723 acre-foot capacity basis. Source: Water Data for Texas (TWDB) daily data.

How full is Cooper (Chapman) Lake?

Cooper (Chapman) Lake is 73.7% full as of September 8, 2026. Its storage is 94% of the September 8 average across its record since 2000. Source: Water Data for Texas (TWDB) daily data.

When was Cooper (Chapman) Lake last full?

Cooper (Chapman) Lake was last at or above 95% of its 258,723 acre-foot capacity basis on August 12, 2025. As of September 8, 2026 it is 73.7% full. Source: Water Data for Texas (TWDB) daily data.

Is Cooper (Chapman) Lake rising or falling?

Cooper (Chapman) Lake is falling: its elevation changed -0.28 feet over the week ending September 8, 2026, -1.32 ft over the past month, and -2.51 feet over the past year. Source: Water Data for Texas (TWDB) daily data.

What was Cooper (Chapman) Lake's lowest water level on record?

Cooper (Chapman) Lake's lowest surface elevation in the daily record since October 1, 2000 was 422.02 feet on December 28, 2006, per the daily record used by this site. As of September 8, 2026 the reservoir is 13.94 feet above that record low.

About this gauge

Cooper (Chapman) Lake is a Texas water-supply reservoir in the Sulphur River basin. Water Data for Texas publishes a conservation pool elevation of 440.0 ft and a conservation capacity of 258,723 acre-feet, with daily water level and storage recorded since 1993-10-02.

Operator

Texas Water Development Board (Water Data for Texas)

Station

jim-chapman

Measurements

Daily water level and conservation storage

River

Sulphur River

State

Texas

Full pool reference

440.0 ft

Capacity basis

258,723 acre-feet (Water Data for Texas (TWDB) conservation capacity)

Period of record

October 1, 2000 (TWDB's period of record for this reservoir)

Status

Provisional - subject to revision by the reporting agency

Update cadence

Daily

TWDB reports conservation storage against a conservation capacity that is restated as new volumetric surveys are completed, so a percent-full figure here can change without the water level changing. TWDB's methodology page is linked in the notes below.

Download the daily CSV (date, elevation ft, storage AF) or see all data downloads.

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