Streamflow Information in Texas

David R. Maidment

Director, Center for Research in Water Resources

University of Texas at Austin

USGS Workshop, Fort Worth, Tx, 9 February 2005

Streamflow Information in Texas

• Texas as part of the National Streamflow Information Program

• Gage network analysis in Texas

• Streamflow information system

Streamflow Information in Texas

• Texas as part of the National Streamflow Information Program

• Gage network analysis in Texas

• Streamflow information system

Current Stream Gaging Network(~ 7000 gages)

Water Watch – Real Time Data(~ 5000 gages)

National Streamflow Information Program• What gages need

to be federally supported?

• Five goals with associated GIS metrics

• Recent National Academy report

National Academy Press http://www.nap.edu

NSIP Goals1. Interstate and International Waters

(Borders and Compacts)

2. Flood Forecasts (NWS sites)

3. River Basin Outflows (Water Budgets)

4. Sentinel Watersheds (Regionalization and Long Term Trends of “natural flows”)

5. Water Quality (NAQWA, NASQAN,…

1. Interstate and International Waters(515 gage sites)

Metric: Operate a discharge station at rivers:• on or near crossings of state and international borders where the drainage area of the river reach is greater than 500 square miles, • or where the location is mandated by a treaty, compact or decree

2. NWS Forecast Points (3244 Gage sites)

Metric: Operate a streamgaging station at each NWS and NRCS forecast point that is not located on a reservoir

3. River Basin Outflows(450 gage sites)

Metric: Operate streamgaging stations near the terminus of each of the 352 Hydrologic Accounting Units (6-digit HUC’s) for water budgeting purposes

4. Sentinel Watersheds (874 Gage sites)

Regionalization and Long Term Trends in Streamflow(stations measuring natural flow in undisturbed lands)

Ecoregion

5. Water Quality (210 gage sites)

Metric: Locate a stream gage on the same river reach as a permanent water quality monitoring site

All NSIP Stations (4424 gage sites)

Source of NSIP Gage Sites

• Active USGS gages 2796 (63%)

• Other agency gages 307 (7%)

• Inactive gages 837 (19%)

• New gages 484 (11%)

3103 existing gages (70%)1221 inactive or new gages (30%)

NSIP Gages

0 50 100 150 200 250 300 350 400 450

Texas

Kansas

Montana

Illinois

Utah

New Mexico

Arkansas

Wyoming

Georgia

Mississippi

Indiana

Ohio

South Dakota

Nevada

Massachusetts

Maryland

Vermont

Number of NSIP Gage Sites

Texas (416)California (201)

Colorado (171)Kansas (166)

Rhode Island (2)Delaware (4)

Streamflow Information in Texas

• Texas as part of the National Streamflow Information Program

• Gage network analysis in Texas

• Streamflow information system

Stream Gages in Texas19

00

1910

1920

1940

1930

1950

1960

1980

1970

1990

Daily Mean Flows

Peak Flows

200

300

400

Existing: 312 daily stations, 17 annual peak stations

1962

1900

1910

1920

1940

1930

1950

1960

1980

1970

1990

Back to 1962

Existing: 312 daily stations, 17 annual peak stations

1900

1910

1920

1940

1930

1950

1960

1980

1970

1990

NSIP Goal: 416 daily stations

NSIP Goals vs Existing Stations

Texas Stream Gaging Network

Active Stations

Discontinued Stations

Texas Gage Network Assessment

• Carried out by USGS and Texas Water Development Board (principal local cooperator)

• Goals– Regionalization – estimate flows or flow

characteristics at ungaged sites in 11 hydrologically similar regions

– Major Flow – obtain flow rates and volumes in large streams

– Outflow from the State – account for streamflow leaving the State

– Streamflow conditions assessment – assess current conditions with regard to long-term data and define temporal trends in flow

River Basins and Hydrologic Regions

Regional Optimization Model

• Based on Generalized Least Squares Regression – separates model error from error due to finite sample size

• Estimating mean annual flow and 25 year peak flow using basin characteristics with equations for each hydrologic region

• Three planning horizons (5yr, 10yr, 20yr)• Active or discontinued stations in natural

watersheds considered• Start with all stations then step backwards,

eliminating least informative station at each step

• As number of stations increases, sampling error decreases until a minimum is reached• As planning horizon increases, sampling error decreases

5yr

5yr5yr

10yr

10yr

10yr

20yr

20yr

20yr

Estimating the 25-year Peak StreamflowM

ean

Sam

plin

g E

rror

Number of Stations

Results of Regional Optimization

• Stations on steepest part of the curve offer the most valuable regional hydrologic information relative to basin characteristics

• Sampling error increases as you go west and climate gets drier– Mean annual flow 6.6% to 114.3%– 25yr peak flow 9.9% to 28.5%

• Much less error in regression equations for 25yr peak flow than mean annual flow in arid regions

• Greater variability in error between regions than by adding stations within a region

Flow Correlations

• Strong correlation in flows for upstream and downstream stations on the same river– 61 of 81 station pairs analyzed for mean

annual flow have correlation coefficient > 0.9– 43 of 129 station pairs analyzed for 25 year

flow have correlation coefficient > 0.9

• Select stations for core network that are not highly correlated with other selected stations

Interstation Correlation of Mean Annual Flow

> 0.950.9 – 0.95< 0.9

Correlation Coefficient

Figure 12

> 0.950.9 – 0.95< 0.9

Correlation Coefficient

Interstation Correlation of 25yr Peak Flow

Results of Texas Study

• Proposed core network of 263 stations for regional hydrology purposes in natural watersheds– 205 active stations (78%)

• NSIP for Texas requires 416 stations– Border (10), NWS (345), Basin (36), Sentinel (87),

Water Quality (16) (some gages serve multiple goals)

• Existing Gage Network of 312 stations• Difficult to make comparisons between national

and regional studies because criteria are different

Streamflow Information in Texas

• Texas as part of the National Streamflow Information Program

• Gage network analysis in Texas

• Streamflow information system

Streamflow Information System

“The stream gaging activity is no longer considered a network of observation points, but rather an information system in which data are provided by both observation and synthesis”

(Fontaine et al, 1984, “Cost Effectiveness of the Stream-Gaging Program in Maine”, USGS Water Supply Paper 2244)

Water Watch – Real Time Data(~ 5000 gages)

Streamstats

Space

Historical dailymean discharge

Streamflow statistics

Real Time data

Streamflow Information in Space and Time

Time

At Gages Anywhere on a Stream

Future PossibilitiesCurrent

Streamstats

Numerical Weather Prediction(North American Regional Reanalysis)

Precipitation Evaporation

3 hour time steps, 32 km grid, 1979 -- 2003

Real-time bacteria estimation

Kansas River at DeSoto, KS

Point Design Model

Gage

Domain

Site gages so as to accurately measure the verticalflux (e.g. precipitation) over a domain

Coverage Design ModelTake a space and subdivide it into subspaceswith an area for each point e.g. service areas of fire stations (goal of 4 min response time to a call)

NWS forecast Watersheds(flooding)

EPA TMDL Segments(water quality)

TCEQ water availability points(water supply)

GuadalupeHydroNetwork

Coverages of the Guadalupe Basin

San Marcos basin as a coverage model

124

3

56

Instream Flows in Texas

• Senate Bill 2 in 2001 Texas Legislature authorizes legal protection of instream flow

• Study program on selected reaches underway

• Review by National Academy

Report released Feb 8, 2005

Senate Bill 2

• Implementation is joint responsibility of TWDB, TPWD, TCEQ

• SB2 says: “… conduct studies and analyses to determine appropriate…flow conditions [that]…support a sound ecological environment.”

• Achieving this goal is scientific and institutional challenge for Texas

Instream Flow Studies

• Requires TPWD, TWDB, TCEQ to develop procedures for defining instream flow requirements

• Implemented on priority study regions by 2010

• Based on aquatic life analysis

Priority Study Regions

Guadalupe

San Antonio

Brazos

Trinity

Sabine

River Reach Studies

Combining Flows and Biology

Instream Flow

Decision Making

Hydrodynamic

Model

Habitat

Descriptions

Habitat

Model

ArcGISSMS/RMA2 Data Collection and

some statistics

Depth & velocity

Species groups

Criterion

Biological Gage

• A representative reach associated with a stream gage

• Regular monitoring for aquatic life assessment

• Scientific program for relating flow and ecological integrity

Conclusions• National: number of

stream gages steady, real-time rising

• Texas: number of stream gages declining since peak of ~410 in 1972

• Losing 6 gages per year to less than 290 currently

Texas

National

Texas Needs 416 gages to meet national needs

NSIP Gages

0 50 100 150 200 250 300 350 400 450

Texas

Kansas

Montana

Illinois

Utah

New Mexico

Arkansas

Wyoming

Georgia

Mississippi

Indiana

Ohio

South Dakota

Nevada

Massachusetts

Maryland

Vermont

Texas (416)

Statistical studies have been done to optimize existing gage network

> 0.950.9 – 0.95< 0.9

Correlation Coefficient

We need flows to support lots of different watershed coverages

TCEQ water availability points(water supply)

NWS forecast Watersheds(flooding)

EPA TMDL Segments(water quality)

Guadalupe River Network

We face a major challenge to define instream flows