Title
Receive Report on Salinas Valley Water Conditions for the Fourth Quarter of Water Year 2015-2016
Report
RECOMMENDATION:
It is recommended that the Monterey County Water Resources Agency Board of Directors:
Receive report on Salinas Valley water conditions for the fourth quarter of Water Year 2015-2016.
SUMMARY/DISCUSSION:
This report covers the fourth quarter of Water Year 2015-2016 (WY16), July through September, 2016. It provides a brief overview of water conditions in the Salinas Valley with discussion of precipitation, reservoir storage, and ground water level trends. Data for each of these components are included as graphs and tables in Attachments B through J.
Precipitation - Normally a time of minimal precipitation, the fourth quarter of WY16 brought lower than normal rainfall to Salinas and King City. Cumulative totals for the quarter were 0.00 inches (0% of normal rainfall of 0.20 inches for the quarter) at the Salinas Airport, and 0.00 inches (0% of normal rainfall of 0.17 inches for the quarter) in King City.
Attachment B contains graphs for both stations showing monthly and cumulative precipitation data for the current and a normal water year. Attachment B also includes tables showing values for precipitation totals as well as percent of normal precipitation.
Rainfall data for Salinas and King City should be considered preliminary until verified by National Weather Service data at a later date.
Reservoirs - The following table compares fourth quarter storage at Nacimiento and San Antonio reservoirs for the past two years. Storage in Nacimiento Reservoir is 20,930 acre-feet higher than in September 2015, and storage in San Antonio Reservoir is 11,334 acre-feet higher.
|
Reservoir |
September 30, 2016 (WY16) Storage in acre-feet |
September 30, 2015 (WY15) Storage in acre-feet |
Difference in acre-feet |
|
Nacimiento |
97,780 |
76,850 |
20,930 |
|
San Antonio |
21,863 |
10,529 |
11,334 |
Graphs for both reservoirs showing daily storage for the last five water years along with average daily storage for comparison are included as Attachments C and D.
Groundwater Levels - More than 80 wells are measured monthly throughout the Salinas Valley to monitor seasonal groundwater level fluctuations. Data from approximately 50 of these wells is used in the preparation of this report. The measurements are categorized by hydrologic subarea, averaged, and graphed to compare current water levels with selected past conditions. Graphs for individual subareas, showing the current year’s water level conditions, last year’s conditions (WY15), dry conditions (WY91), and near-normal conditions (WY85), are found in Attachments E through I. Attachment J is a summary of water level changes for all subareas.
Groundwater level measurements indicate that, by the end of the fourth quarter of WY16, water levels were recovering in the Pressure and East Side Subareas, though not in the Forebay or Upper Valley Subareas. Over the past month, average groundwater levels rose by two feet in the Pressure 400-Foot Aquifer, five feet in the East Side Subarea and less than a half foot in the Pressure 180-Foot Aquifer. Groundwater levels declined in the Forebay and Upper Valley Subareas, by one foot and two feet, respectively, over the past month.
Compared to September 2015, average groundwater levels in September 2016 were down by six feet and five feet in the Upper Valley and Forebay Subareas, respectively, while rising by six feet in the East Side Subarea, and by one foot in the Pressure 400-Foot Aquifer. September 2016 groundwater levels in the Pressure 180-Foot Aquifer were virtually unchanged from September 2015 levels.
When compared to WY85, which is considered to be a year of near normal groundwater conditions, current water levels are 22 feet lower in the East Side Subarea, 20 feet lower in the Forebay Subarea, 19 feet lower in the Upper Valley Subarea, 17 feet lower in the Pressure 180-Foot Aquifer and one foot lower in the Pressure 400-Foot Aquifer.
Average groundwater levels for the fourth quarter of WY16 remained below WY91 (dry condition) levels in the Pressure 180-Foot Aquifer as well as the Forebay and Upper Valley Subareas. By contrast, throughout the fourth quarter, water levels in the Pressure 400-Foot Aquifer remained five to seven feet higher than in WY91, while groundwater levels in the East Side Subarea rebounded to WY91 levels by the end of the fourth quarter of WY16.
OTHER AGENCY INVOLVEMENT:
None
FINANCING:
Funds 113, 114, 115, 116
Prepared by: Howard Franklin, Senior Hydrologist, (831) 755-4860
Peter Kwiek, Hydrologist, (831)755-4860
Approved by:
David E. Chardavoyne, General Manager, (831) 755-4860
Attachments:
1. Attachment A, Salinas Valley Hydrologic Subareas Map
2. Attachment B, Salinas and King City Precipitation Graphs
3. Attachment C, Nacimiento Reservoir Graph
4. Attachment D, San Antonio Graph
5. Attachment E, Groundwater Trends Pressure 180-Foot Aquifer
6. Attachment F, Groundwater Trends Pressure 400-Foot Aquifer
7. Attachment G, Groundwater Trends East Side Subarea
8. Attachment H, Groundwater Trends Forebay Subarea
9. Attachment I, Groundwater Trends Upper Valley Subarea
10. Attachment J, Groundwater Trends Summary