streamflow information in texas
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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 - PowerPoint PPT PresentationTRANSCRIPT
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