NHI Layers for Groundwater Vulnerability Assessment. Interim Update - DRAFT. September 16, 2014

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1 NHI Layers for Groundwater Vulnerability Assessment Interim Update - DRAFT September 16, 2014

2 Outline NHI refresher Development of NHI layers and assumptions Soil Crop Irrigation Draft NHI scores Next steps Interpretations

3 NHI Refresher Index and overlay method Uses relative rankings (index), not absolute, measurable values Considers three N leaching factors simultaneously (overlay) Considers the three most important factors related to N leaching Soil (ranked 1 to 5) Crop (ranked 1 to 4) Irrigation (ranked 1 to 5)

4 Soil Layer Data Source SSURGO (NRCS) electronic database of soil maps and soil type characteristics Development NHI value of a soil series that is a complex (includes more than one soil type) is an area-weighted average Assumptions All permanent crop soils are deep-ripped to 2-5 feet. This increases the NHI value by 2 (compared to no deep ripping)

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6 Crop Layer Data Source Kern County spatial crop database Development field boundary corrections on permanent crops to Rectify boundaries with imagery Ensure correct acreage Assumptions NHI values of fields that are double or triple cropped are averages of those crop values

7 Example NHI Crop Values 1 - Grapes, olive, dried bean, fig 2 - Alfalfa, almond, apple, barley, blueberry, carrot, citrus, corn for fodder, cotton, oat, pasture, stone fruit, sweet potato, walnut, wheat 3 - Asparagus, corn for grain/sweet, melons, kiwi, potato, tomato, turf 4 - Lettuce, cabbage, cilantro, onion, strawberry

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9 Irrigation Layer Data Source KRWCA districts and DWR (2006) Development Merged district datasets with Kern Co. crop dataset Assumptions location of irrigation type needed only for some districts Assumed all drip and sprinkler irrigated crops are fertigated (not an option for surface irrigation)

10 NHI Irrigation Values 1 - Micro/drip with fertigation 2 - Sprinkler with fertigation 3 - Sprinkler - surface average 4 - Surface

11 Irrigation Layer (continued) Current spatial irrigation survey information Arvin Edison Henry Miller Kern-Tulare North Kern Olcese Rosedale-Rio Bravo Semitropic Wheeler-Ridge Maricopa

12 Irrigation Layer (continued) Current non-spatial irrigation survey information SSJMUD Many crops only one irrigation type (manually assigned) Grapes, almonds and alfalfa two main irrigation types General survey information Kern-Delta Used general assumptions developed from district staff s anecdotal information Perm (drip); potatoes/tomatoes (sprinkler); cotton/alfalfa/corn (surface); veggies (average sprinkler + surface)

13 Irrigation Layer (continued) No general survey information Shafter-Wasco Used 2006 DWR data No information Un-districted area (DWR) Tehachapi-Cummings (DWR)

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15 NHI Results Multiplicative index soil, crop and irrigation index values are multiplied together for each field Original documentation 20 or below indicates low nitrate leaching risk 21 or over indicates higher nitrate leaching risk Refined groupings may help coalition prioritize, but will not be presented in GAR

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18 Refinements Next Steps Refine Layers Review assumptions irrigation Rectify field boundaries where district datasets and Kern Co. dataset don t match up Review information and assumptions double and triple cropping, two types of irrigation, deep ripping, fertigation Fill in data gaps district staff, ground-truthing, etc.

19 NHI Analysis and Interpretation NHI results reviewed and interpreted Lake bottom farming Unique cropping/irrigation management Age of permanent crops? Limitations Anticipated refinements for 5-year update

20 Interpretations Currently an interim, draft product Initial results are consistent with what we have been saying for 2+ years now Kern Sub Basin is different (e.g. Buena Vista Lake Bed) Kern Sub Basin is highly efficient in irrigation practices The NHI is a good predictor of nitrate leaching risk in the Kern Sub Basin

21 Interpretations Interesting trends and comparisons East side soils and irrigation methods vs Buena Vista soils and irrigation methods See examples

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24 Interpretations Expert Panel Conclusions Currently still state that a vulnerability classification should be abandoned, however this clearly contradicts with individual orders In lieu of that, indicated that an NHI is suitable for preliminary conclusions Until the Application/Removal ratio has been developed Envisioning a combination of NHI and A/R

25 Interpretations Development of the master spatial database by field: Facilitates analyses like the NHI and also the Application/Removal ratio Provides proof/justification of where to most effectively spend resources Provides for clear and concise display of spatial information A comprehensive tool that the coalition can use moving forward for a variety of purposes