BASIN MANAGEMENT OBJECTIVES WESTERN CANAL WATER DISTRICT SUBINVENTORY UNIT

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1 BASIN MANAGEMENT OBJECTIVES WESTERN CANAL WATER DISTRICT SUBINVENTORY UNIT Butte County Water Advisory Committee Member Anjanette Shadley Martin Contact Information: Phone Number: Address: Description of the Western Canal Sub-Inventory Unit The Western Canal Sub-Inventory Unit (SIU) covers an area of about 44,750 acres. About one-third of the sub-inventory unit is in the West Butte Inventory Unit and the remainder is in the East Butte Inventory Unit. The Western Canal SIU corresponds roughly to the Butte County portion of the Western Canal Water District. A portion of the southwestern corner of the water district is in Glenn County. Agricultural production in the Western Canal SIU consists primarily of rice supported by surface water. In normal years, about 7% of the SIU is in summer agricultural production supported by groundwater. During drought years, the area of summer agricultural production supported by groundwater increases to about 13%. The data presented in this section includes the entire Butte County portion of the Western Canal SIU. Management Objective To maintain sufficient volumes of groundwater in storage within the Upper and Lower Tuscan Formation aquifer systems to provide an adequate and affordable irrigation water supply, of adequate quality for agriculture purposes, including during periods of extended drought and to assure that groundwater in storage is not depleted over time. It is the intent of this management objective to assure a sustainable agricultural water supply now and into the future and to assure the water supply can be utilized without injuring groundwater quality or inducing land subsidence. The management objective is also to assure an adequate supply for groundwater from the alluvial aquifer system for all domestic users in the sub-inventory unit. Geologic Formations Identified In Sub-Inventory Unit - Geologic formations in the Western Canal SIU from youngest (shallowest) to oldest (deepest) include: Basin Deposits Laguna Formation Tuscan Unit C (Upper Tuscan) Tuscan Unit B (Lower Tuscan) Fresh Water-bearing Units - In the Sacramento Valley Region of Butte County, fresh groundwaterbearing units include, from youngest (shallowest) to oldest (deepest), the Modesto, Riverbank, Laguna, Tehama and Tuscan Formations. Those included in the Western Canal SIU are: Laguna Formation Tuscan Unit C (Upper Tuscan) Tuscan Unit B (Lower Tuscan) Western Canal 2015 BMO 1

2 BMO Key Wells Selected for Groundwater Level Monitoring (Specific Depth Method) SPRING The Western Canal SIU uses the specific depth method to establish alert stages. As described in Butte County Code, Chapter 33A, this method sets alert stages for spring levels only. Well ID First Aquifer Stage 1/2 Alerts Stage 3 Alerts Well Type Record System Elev. (ft) Depth (ft) Elev. (ft) Depth (ft) 19N01E09Q01M 1991 Lower Tuscan Irrigation N01E18L01M 2000 Lower Tuscan Monitoring N01E18L02M 2001 Upper Tuscan Monitoring N01E18L03M 2001 Alluvial Monitoring N01E35C01M 1947 Alluvial Domestic N02E16P01M 1990 Unknown Irrigation N02E28N01M 1947 Alluvial Domestic **2013 Note: Some alert stage elevations have changed slightly due to a change in the vertical datum in the state s database, CASGEM. Numbers are now consistent with CASGEM. Other wells monitored in the SIU have short periods of record and therefore do not have assigned alert levels. However they are tracked to monitor changing groundwater conditions from year to year. These include: 19N02E07K a multi-completion well added in N02E13Q a multi-completion well added in N02E13Q001 a monitoring well added in N02E15H001 and 20N02E15H002 monitoring wells added in 1995 BMO Key Wells Selected for Groundwater Quality Monitoring Groundwater Temperature ( o C) State Well Number N02E15R01M NM N01E15D01M Groundwater ph State Well Number N02E15R01M NM N01E15D01M Groundwater Electrical Conductivity (µs/cm) State Well Number N02E15R01M NM N01E15D01M Western Canal 2015 BMO 2

3 BMO Key Well(s) Selected for Land Subsidence Monitoring State Well Number 20N01E18L03M, located within the SIU is monitored continually. Maximum annual inelastic land subsidence shall not exceed 0.01 feet per year. Western Canal Water District SIU Stakeholder Issues and Recommendations Current Conditions Approximately 1000 acres transitioned in 2013 from rice to walnuts in the northeast corner of the District boundary at Nelson/Shippee Road at Gage Road using a mix of ground and surface water where it was traditionally served by surface water only. Future Monitoring Recommendations - Efforts to identify additional domestic wells to enhance the existing sub-inventory monitoring well network for the development of management objectives in the alluvial aquifer system. Efforts will also be made to identify more wells in all aquifers which meet the criteria developed. Western Canal 2015 BMO 3

4 Supporting Data Groundwater Level Hydrographs Hydrographs on the following pages depict yearly spring groundwater level measurements with established alert levels. WSE Water Surface Elevation (feet, above mean sea level) QM Questionable Measurement KEY Well: 20N01E35C001M This well has long been a Key Well highlighted in the Butte Basin Water Users Annual Report. The figure below is a hydrograph for an active domestic well 20N01E35C001M, in the central portion of the Western Canal sub-area. The area surrounding this well is characterized as rural agricultural. Agricultural cultivation in this area consists of rice production supported by surface water in normal years and a combination of surface and groundwater in drought years. The well is constructed in the uppermost aquifer system. The groundwater level measurement for this well dates back to Groundwater levels in this well were monitored on a semi-annual basis until 1991, and on a monthly basis from 1991 to about Since 1995 this well is being monitored four times a year during March, July, August and October. The spring to fall fluctuation in groundwater levels averages less than 3 feet during years of normal precipitation and the same during years of drought. Summer groundwater level monitoring indicates the water table in the upper aquifer rises during summer months due to flood irrigation for rice production producing groundwater level measurements that are higher in the summer than in either the spring or fall. Long-term comparisons of spring-to-spring groundwater levels show almost no change associated with the , and 1994 drought periods. Further long-term analysis of spring-to-spring groundwater levels indicates very little change since monitoring began in Water elevations have been monitored since 1947 at this location and the historical average depth to water, including 2014, is about 3 feet in the spring and about 4 feet in the fall below ground surface. No spring measurement was taken in 2012 or 2014 due to the well being pumped at the time of monitoring. Western Canal 2015 BMO 4

5 WSE Water Surface Elevation (feet, above mean sea level) Western Canal 2015 BMO 5

6 WSE Water Surface Elevation (feet, above mean sea level) Western Canal 2015 BMO 6

7 WSE Water Surface Elevation (feet, above mean sea level) Western Canal 2015 BMO 7

8 The last data point in the spring hydrograph was taken in April and should not be evaluated as a BMO value. The Spring 2014 BMO measurement for 20N02E16P001M is the second to last measurement in the hydrograph. It was taken on March 21, The last data point in the spring hydrograph was taken in April and should not be evaluated as a BMO value. The Spring 2014 BMO measurement for 20N02E28N001M is the second to last measurement in the hydrograph. It was taken on March 21, WSE Water Surface Elevation (feet, above mean sea level) Western Canal 2015 BMO 8

9 Monitored Wells without Alert Stages WSE Water Surface Elevation (feet, above mean sea level) Western Canal 2015 BMO 9

10 WSE Water Surface Elevation (feet, above mean sea level) Western Canal 2015 BMO 10

11 WSE Water Surface Elevation (feet, above mean sea level) Western Canal 2015 BMO 11

12 WSE Water Surface Elevation (feet, above mean sea level) Western Canal 2015 BMO 12