Lyons Method

Lyons MethodLyons Method

Chris LoftChris Loft

Texas Commission on Environmental QualityTexas Commission on Environmental Quality Water Rights Permitting & Availability SectionWater Rights Permitting & Availability Section

Lyons and Bounds StudyLyons and Bounds Study

• The TPWD study initiated to determine The TPWD study initiated to determine minimum streamflows needed to support minimum streamflows needed to support Texas stream fisheriesTexas stream fisheries

• Minimum flows should provide necessary Minimum flows should provide necessary flow during critical periods and maintain flow during critical periods and maintain adequate aquatic habitat.adequate aquatic habitat.

Texas Water CodeTexas Water Code

• Since 1985, the Texas Water Code has Since 1985, the Texas Water Code has required the Commission to assess required the Commission to assess effects of a water use permit on:effects of a water use permit on:– Existing instream usesExisting instream uses– Water qualityWater quality– Fish and wildlife habitatFish and wildlife habitat– Freshwater inflow needs for bays and Freshwater inflow needs for bays and

estuariesestuaries

Currently…Currently…

• Environmental reviews of water right Environmental reviews of water right applications are conducted on a case-by-applications are conducted on a case-by-case basiscase basis

• In the absence of site-specific data, TCEQ In the absence of site-specific data, TCEQ relies mainly on the Lyons Method and/or relies mainly on the Lyons Method and/or 7Q2 value for calculating instream flows7Q2 value for calculating instream flows

Currently…Currently…

Factors that contribute to the requirement of Factors that contribute to the requirement of a streamflow restriction include:a streamflow restriction include:

• Perennial nature of the streamPerennial nature of the stream

• Aquatic life use and biological integrity of Aquatic life use and biological integrity of the streamthe stream

• Water quality issuesWater quality issues

• Presence of species of concernPresence of species of concern

• Recreational usesRecreational uses


• Based on historical daily gaged flow Based on historical daily gaged flow datadata

• Period of recordPeriod of record

• Ungaged locationsUngaged locations

• Method provides for 40% of median Method provides for 40% of median monthly flows October – February and monthly flows October – February and 60% March - September60% March - September


• Determines minimum flow requirements Determines minimum flow requirements for habitat protectionfor habitat protection

• Provides more flow during critical spring Provides more flow during critical spring and summer monthsand summer months

7Q27Q2

• Lowest average streamflow for seven Lowest average streamflow for seven consecutive days with a recurrence consecutive days with a recurrence interval of two yearsinterval of two years

• Statistically derived from historical daily Statistically derived from historical daily gaged flow data gaged flow data

• Minimum flow that would sustain water Minimum flow that would sustain water qualityquality

7Q27Q2

• Low flow value used in water quality Low flow value used in water quality modeling for TPDES permittingmodeling for TPDES permitting

• Where the 7Q2 value is greater than the Where the 7Q2 value is greater than the Lyons numbers, 7Q2 is usedLyons numbers, 7Q2 is used

Instream Flow Recommendations Instream Flow Recommendations using Lyons Method and 7Q2 flowsusing Lyons Method and 7Q2 flows

0

50

100

150

200

250

300

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

cfs

Median Lyons 7Q2

Example of Flow RestrictionExample of Flow Restriction

“ “In order to provide sufficient flows for the instream In order to provide sufficient flows for the instream uses of the Green River, diversions of water should uses of the Green River, diversions of water should be limited to times when streamflow equals or be limited to times when streamflow equals or exceeds the following monthly flows at USGS exceeds the following monthly flows at USGS gaging station #08000000:”gaging station #08000000:”

Recommended monthly flows (cfs)Recommended monthly flows (cfs)

Jan Feb Mar Apr May Jun Etc.

11 14 37 40 64 40 Etc.

Instream Flow Recommendations Instream Flow Recommendations

0

50

100

150

200

250

300

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

cfs

Median Lyons Grouped Lyons


121 cfs for Mar-Jun121 cfs for Mar-Jun

59 cfs for Jul-Feb59 cfs for Jul-Feb

Desktop ReviewDesktop Review

• Science Advisory Committee report (2006) Science Advisory Committee report (2006) recommended a review of desk-top recommended a review of desk-top methodologiesmethodologies

• TCEQ contracted with scientists (TRG) for a TCEQ contracted with scientists (TRG) for a review of Desk-top methods for establishing review of Desk-top methods for establishing environmental flowsenvironmental flows

• Report completed in August 2008.Report completed in August 2008.

Lyons MethodLyons Method Advantages Advantages

• Simple to estimate flow requirementsSimple to estimate flow requirements

• Easy to incorporate into the permitting Easy to incorporate into the permitting processprocess

• Easy for the regulated entity or permittee to Easy for the regulated entity or permittee to understandunderstand

Lyons MethodLyons Method Disadvantages Disadvantages

• Method established based on extremely limited data Method established based on extremely limited data and may not be applicable throughout the stateand may not be applicable throughout the state

• Limited validation against biological dataLimited validation against biological data

• Provides only minimum flows instead of the flow Provides only minimum flows instead of the flow variability now recognized as necessary for variability now recognized as necessary for ecological integrityecological integrity

Recommendations from the TRGRecommendations from the TRG

• In the absence of further information In the absence of further information and for the sake of continuity, continue and for the sake of continuity, continue applying the Lyons Method as a applying the Lyons Method as a desktop methodologydesktop methodology

• Conduct field studies to validate and Conduct field studies to validate and assess the appropriate spatial assess the appropriate spatial boundaries for regional adjustments to boundaries for regional adjustments to the Lyons Methodthe Lyons Method

Contact Information

Chris Loft (512) [email protected]

mailto:[email protected]

Documents

Lyons Method