Environmental Flows Allocation Process in Texas Kevin Mayes Texas Parks and Wildlife Department March 2010
Senate Bill 3-2007
Environmental Flow Regime A schedule of flow quantities that reflects seasonal and yearly fluctuations that typically would vary geographically, by specific location in a watershed, and that are shown to be adequate to support a sound ecological environment and to maintain the productivity, extent, and persistence of key aquatic habitats in and along the affected water bodies.
Senate Bill 2 Texas Instream Flow Program (2001)
Instream Flow Components (as recommended by National Research Council 2005)
Primary Disciplines Hydrology & Hydraulics Physical Processes (Geomorphology) Connectivity Biology Water Quality
Integration of Flow Components Overbank Flows 4,000-10,000 cfs for 2-3 days Once every 3-5 years Channel Maintenance Riparian Connectivity, Seed dispersal Flooplain habitat Wet year Average year Dry year High Flow Pulses 700-1500 cfs for 2-3 days 2-3 X per year every year Sediment transport Lateral connectivity Fish spawning 1800 cfs for 2 days 1 X per yr every other year Big River fish spawning between Jul 15 - Aug 15 Base Flows 100-150 cfs Fish habitat 300-450 cfs maintain biodiversity and longitudinal connectivity 150-300 cfs Spring spawning 40-50 cfs Fish habitat 90-100 cfs Fish habitat Subsistence Flows 35-55 cfs Maintain water quality (35 cfs) and key habitats in May (55 cfs) JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
Senate Bill 3-2007
Science Advisory Committee Guidance Documents Use of Hydrologic Data in the Development of Instream Flow Recommendations for the Environmental Flows Allocation Process and the Hydrology-Based Environmental Flow Regime (HEFR) Methodology Geographic Scope, Sediment Transport, Freshwater Inflows, Biology and Water Quality, and Implementation
HEFR Basics Uses hydrologic data Computations are rapid Populates a flow regime matrix A hydrological tool for an ecological purpose (1) Select Flow Gage (2) Select Period of Record (3) Separate (parse) Hydrograph into Flow Components (4) Generate Statistical Summaries in Excel
Separate (parse) Hydrograph Option (1) IHA Environmental Flow Components function/tab Option (2) MBFIT USBR algorithm adapted for Texas Both split the hydrograph into IFCs Flow (cfs) 24,000 18,000 12,000 USGS streamflow data Flow Flow (cfs) 24,000 18,000 12,000 Pulse Base Flow 6,000 6,000 0 0 Jan Feb Mar Apr May Jun Jul Date Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Date Aug Sep Oct Nov Dec
IHA EFC
IHA Parsed Hydrograph 24,000 18,000 Pulse Base Flow 12,000 6,000 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Date Flow (cfs)
Input to HEFR to Generate Statistical Summaries HEFR uses Excel to generate summary statistics of each EFC Subsistence (Extreme Low) Base Flow (Low Flow) High Flow Pulses Overbank Events Outputs may include: flow, volume, duration, frequency
HEFR Input Screen
Subsistence Flows Ecological Hypotheses Protect water quality Maintain key habitats HEFR can calculate a user defined statistic e.g., 10 th percentile of base or low flows ~or~ User can input a recommendation based on other information Protect water quality (e.g., 7Q2 used in Texas) Maintain some known flow-ecology relationship
Base Flows Ecological Hypotheses Provide suitable habitat Maintain diversity Maintain water table for riparian veg Provide connectivity along channel HEFR calculates statistics seasonally and monthly, at three user-specified percentiles (often termed dry, average, and wet)
High Flow Pulses Ecological Hypotheses Flush out silt and fines; transport sediment Prevent riparian vegetation from encroaching into channel Restore water quality following drought Provide spawning cues Provide connectivity to oxbows HEFR has two options Original, percentile-based approach More prescriptive, seasonal basis only Alternate, frequency-based approach More flexible, can handle multi-year intervals
Overbank Flows Ecological Hypotheses Shape and redistribute physical habitats Purge invasive species Recharge floodplain water table Provide migration and spawning cues Facilitate exchange of nutrients, sediments, woody debris HEFR has two options Original, percentile-based approach Median of historical overbank flows Alternate, frequency-based approach More flexible
Initial Flow Regime Matrix
Initial Flow Regime Matrix
Overlays Other disciplines can be used to guide HEFR parameterization or as direct overlays that replace initial hydrology-based recommendations: Water Quality Fluvial Sediment Transport Biology Freshwater Inflows to B&Es
Senate Bill 3-2007
Constraints Time Limited (one year for BBEST) Flexibility & Complexity = Many Decisions Although Qualitative Data Relatively Abundant, Quantitative Basin-specific Data Limited e.g., instream flow assessments are uncommon Science and Politics
Information Texas Environmental Flows Process www.tceq.state.tx.us/permitting/water_supply/ water_rights/eflows Environmental Flows Advisory Group Science Advisory Committee Environmental Flows Resources - SAC Guidance and HEFR tools Bay-Basin Expert Science Team pages Texas Instream Flow Program www.twdb.state.tx.us/instreamflows/