ADWR’S JUNE 2009 ADWR’S JUNE 2009 SUBFLOW ZONE SUBFLOW ZONE

REPORTREPORT

by Rich BurtellArizona Department of Water Resources

October 2, 2009

BackgroundBackground

• General stream adjudications are judicial proceedings to determine the nature, extent and relative priority of water rights in a river system [A.R.S. §45-252(A)]

• Arizona has two general stream adjudications – Gila River and Little Colorado River systems

• River systems include all appropriable water and water subject to federal law

• Superior Court for Maricopa County is overseeing the Gila River Adjudication which includes the San Pedro River Watershed

• Adjudication Court has jurisdiction over wells determined to be withdrawing ‘subflow’ (Gila IV)

Background (continued)Background (continued)• Subflow includes “those waters which slowly find their

way through the sand and gravel constituting the bed of the stream, or the lands under or immediately adjacent to the stream, and are themselves a part of the surface stream. It is subject to the same rules of appropriation as the surface stream itself.” (Southwest Cotton, 1931)

• In the San Pedro River Watershed, the subflow zone is defined as ‘saturated floodplain Holocene alluvium’ (Gila IV)

• If a well is located within the subflow zone, it is presumed to be withdrawing subflow (Gila IV)

• Procedures to map subflow zones in the San Pedro River Watershed (2005 Subflow Order)

Subflow Zone CriteriaSubflow Zone Criteria

• Three categories based on Gila IV and 2005 Subflow Order

• Hydrologic – Predevelopment perennial and intermittent stream reaches

• Geologic – Floodplain Holocene Alluvium (FHA)

• Hydrogeologic – Lateral extent of FHA assumed to be saturated with setbacks for side recharge

ADWR’s Hydrologic AnalysisADWR’s Hydrologic Analysis

• Compiled evidence of predevelopment streamflows

• Early evidence Historic accounts Historic irrigation ditch diversions and ore mills 1935 aerial photographs Early streamflow and diversion measurements

• Recent evidence Instream flow claims Wet/dry surveys Recent streamflow and diversion measurements

ADWR’s Geologic AnalysisADWR’s Geologic Analysis

• Arizona Geological Survey (AZGS) contracted to map extent of FHA

• 1:24,000-scale mapping along major streams in watershed

• Identified surface geologic units in approximately 1-mile strips along either side of the streams

ADWR’s Hydrogeologic AnalysisADWR’s Hydrogeologic Analysis

• Entire lateral extent of FHA assumed to be saturated (2005 Subflow Order)

• Applied ‘setbacks’ to account for potential affects of side hydrostatic pressure (1994 Subflow Order) 100-feet where FHA bordered by basin fill 200-feet where FHA bordered by tributary

Holocene alluvium

ADWR’s Subflow Zone MapsADWR’s Subflow Zone Maps

• Delineated on USGS quad maps (Appendix E of report)

• Includes major streams in watershed San Pedro River Babocomari River Aravaipa Creek

• Widths range from 0 to nearly 5000 feet

Report Noticing and AvailabilityReport Noticing and Availability

• Report issued by ADWR on June 30, 2009

• Notice sent to all watershed claimants and court-approved mailing list for Gila Adjudication

• Report availability- Local libraries (Benson, Bisbee, Mammoth, Sierra Vista,

and Tucson AMA) ADWR website DVD ($10)

Hard copy ($100)

Objections to Subflow ReportObjections to Subflow Report• Due December 28, 2009

• Limited to ADWR’s finding regarding lateral extent of subflow zone

• Use objection form posted on ADWR website Must hold Statement of Claimant (SOC) in

watershed State reason(s) for objection Send copy of objection to court and court-approved

mailing list

Next StepsNext Steps• Adjudication Court will consider objections to

ADWR’s subflow report due on 12/28/09

• ADWR will modify its subflow zone maps, as necessary

• Court will approve and issue final subflow zone maps

• ADWR will apply cone of depression tests to identify wells located outside of subflow zone that are impacting the subflow zone

• See 2005 Subflow Order

Wells in the San Pedro River Wells in the San Pedro River WatershedWatershed

• Adjudication Court has jurisdiction over wells within subflow zone and wells determined to be impacting the subflow zone (Gila IV)

• Use of these wells, surface water and federal reserved rights will be subject to a priority system

• Wells not within or impacting the subflow zone are governed by the reasonable use doctrine

ReminderReminder

• All persons using a well in the adjudication areas should file a SOC or confirm one has been filed on their behalf

• Wells located within or impacting the subflow zone are subject to the jurisdiction of the Adjudication Court

• May lose the right to use water in the river system if you fail to file a SOC [A.R.S. §45-254(F)]

• Contact ADWR for details on filing SOCs