Analysis of the Goleta Groundwater Basin Ground surface

1941 Using ArcHydro Groundwater 1955

Dylan Berry UC Santa Barbara Mike Herrman Geography 176C Bruce Stevenson Krzysztof Janowicz Historic Water Levels Georeferencing and Digitizing the Well Data Erik Young May 2013 The purpose of this project was to analyze the Goleta groundwater basin as a fresh water resource. The analysis utilized ArcHydro Groundwater, an ArcGIS extension, to visualize the groundwater basin from stratigraphy and water level data. The results show that the Goleta Basin contains two main aquifers which together can hold roughly 202,000 acrefeet of groundwater. This poster highlights the major steps of the analysis.

Definitions of ArcHydro Feature Classes Definitions of ArcHydro Attributes WellID: Unique identifier for each well feature Well: point feature indicating well location on Earth’s surface HydroID: Equal to WellID, used to relate borelog table and 1941 Boreline: line visualization showing well depth and geologic strata well feature class 1955 Borepoint: point features existing on top of each geologic layer RefElevation: Elevation of well at Earth’s surface within the boreline TopElevation: Elevation at top of boreline segment Georaster: surface visualization created from interpolation of BotElevation: Elevation at bottom of boreline segment HGUID: Hydrogeologic Unit ID, identifies layers of same composition borepoints HorizonID: indentifier of borepoint that defines a given georaster

Data: Borehole stratigraphy data was provided by two main sources: one study completed in 1951 by JE Upson titled “Geology and Ground-Water Resources of the South-Coast Basins of Santa Barbara, ”, and a second study published in 1962 by Evenson et. al. titled “Yield of the Carpinteria and Goleta Ground-Water Basins, Santa Barbara County, California”. These two studies combined provided detailed soil stratigraphy of 50 wells in the Visualization of Stratigraphy Using Borelines Goleta basin. The wells were then digitized on a georeferenced borehole map, which was included with the Evenson study. Methods: Soil stratigraphy was input manually into a borelog table using Microsoft Excel and imported to the ArcHydro geodatabase using Microsoft Access. The wells were digitized onto a high resolution map using the NAD 1927 datum and State Plane California V FIPS 0405 projection. They were then added to the Well feature class in the geodatabase. Borelines were created from the borelog table using layer elevations, and linked to the existing wells in the geodatabase. From these borelines, borepoints were created and Horizon ID’s were assigned to them. A kriging interpolation was then executed on borepoints of the same horizon. This interpolation was opened in ArcScene and projected on a custom surface to produce a near-3D visualization of the horizon. 1941 This process was completed for geologic formations, simplified soil strata, and water levels. Volumes of each aquifer were calculated from elevation values extracted from the georaster projections, which were averaged and multiplied by the area of the basin. Groundwater Level Contours Artesian Situation Results: Special thanks to: Assumptions: Krzysztof Janowicz. UCSB Geography Volume of Upper Aquifer: 812,605 acrefeet Erin Wetherley. UCSB Geography Area of the Basin: 9,542 acres Volume of Lower aquifer = 1,276,279 acrefeet Grant McKenzie. UCSB Geography Average specific yield: 0.1 Total Volume: 2,088,885 acrefeet Jon Jablonski. UCSB Map & Imagery Library Uniformity of geologic formations Jon Harvey. UCSB Earth Science Keith Clark. UCSB Geography Spatial correlation of geologic formations Groundwater Storage: 208,889 acrefeet Hugo Loaiciga. UCSB Geography Spatial correlation of water levels Dylan Parenti. UCSB Geography Conclusions: Through spatial analysis it was determined that the storage of water-bearing formations in the Goleta basin is 209,000 acrefeet. Discussion: Our estimated volume of 209,000 acrefeet is comparable to that reported by the Goleta Water District of 200,000 acrefeet. Analysis of historical groundwater levels revealed an artesian situation where the groundwater surface elevation might exceed the land surface elevation. This coincides with the location of Goleta , a local . Through the comparison of water table contour maps for the years of 1941 and 1955, it can be determined which wells were responsible for the most drawdown during the 14 year span. These are most likely 10P3, 15G4, and/or 15G3 in the eastern basin, and 8K7, 8J1, and/or 8H1 in the central basin. In examining the georaster model of the upper and lower basin, the upper aquifer coincides with the Younger Alluvium formation (Qac), while the lower aquifer coincides with the Santa Barbara Formation (Qsb). This is confirmed by the model, as the bottom of the upper 1955 Assignment of Horizon IDs aquifer nearly matches the boundary between the formations. Some potential sources of error in our analysis include the subjectivity of the strata simplification process, variation of physical properties within geologic formations, and ambiguity in data interpretation.

Visualization of Geologic Formations Using Georasters Simpli cation of the Strata Kriging the Horizons

Top of Younger Alluvium Formation (Qac) Top of Santa Barbara Formation (Qsb) Boundaries of Upper and Lower Aquifers

These georasters show the geologic formations classi ed as Younger Alluvium (Qa) [top] and the Santa Barbara Formation (Qsb) [bottom]. The Santa Barbara Formation is most likely the location of the major water-bearing aquifer in the basin due to its coarse components and high porosity sand/gravel layers. All study wells in the Goleta area penetrate just to the bottom of the Santa Barbara Formation, and are perforated through this entire section as well. This con rms that local wells draw entirely from the Santa Barbara Formation.