Local Groundwater Flow Model Addendum

Guadalupe Restoration ProjectSan Luis Obispo County

October 24 2002

Reasons for LGFM Revision

• Excess water entering DSA from agricultural fields to the east

• Drainage channel along eastern DSA identified

• Update layer structure to conform with new data

• Overall goals: more realistic water balance, enhance model reliability

Model Revisions

• Changed layer structure– Base of DSA revised throughout GOF

– Top of PA conforms with Worts (1951)

• Included agricultural drainage channel

• Revised recharge and soil properties for agricultural fields

• Revised calibration targets and improved model calibration

Revisions to Layers

Old Layer 5 Bottom

(gray)

New Layer 5 Bottom (colored)

Old DSA Bottom (gray)

New DSA Bottom (colored)

Old PA Top (gray)

New PA Top (colored)

Addition of Agricultural Drain

Drain Location in LGFM 3.0

Agricultural Fields

DSA

Changes to Recharge and Soil Properties

Recharge Rates in LGFM 2.0

3 in/yr

8 in/yr

10.7 in/yr

10.7 in/yr

Recharge Rates in LGFM 3.0

3 in/yr

8 in/yr

3 in/yr

3 in/yr

Hydraulic Conductivities in LGFM 2.0

Kh = 75 ft/day

Kv = 33 ft/day

Kh = 50 ft/day

Kv = 5 ft/day

Hydraulic Conductivities in LGFM 3.0

Kh = 75 ft/day

Kv = 33 ft/day

Kh = 25 ft/day

Kv = 2.5 ft/day

Calibration

5.4

16.5

27.5

38.5

49.5

60.5

5.4 16.5 27.5 38.5 49.5 60.5

Observed Value

Layer 1

Layer 2

Layer 3

Layer 4

Layer 5

Layer 6

Observed vs. Computed Target Values

Recalibration Statistics

Statistic LGFM 2.0 LGFM 3.0

Number of Target Water Levels 368 355

Range of Water Level Targets (ft) 54.75 54.75

Maximum Residual Water Level (ft) 9.28 3.85

Minimum Residual Water Level (ft) -5.02 -4.57

Mean Residual Water Level (ft) -0.61 -0.04

Mean of Residual Absolute Values (ft) 1.53 1.29

Standard Deviation of Residual Water Levels (ft) 1.76 1.54

Sum of Squared Residual Water Levels (ft2) 1,280 846

Standard Deviation of Residuals/Range 0.032 0.028

How Has Flow Balance Changed?

Bottom OutflowBottom Outflow

Bottom InflowBottom Inflow

Lateral OutflowLateral Outflow

Lateral InflowLateral Inflow

Outflow to RiverOutflow to River

Willows OutflowWillows Outflow

Recharge Inflow

Recharge Inflow

Evapotranspiration Outflow

Evapotranspiration Outflow

Drain Outflow Drain Outflow

Flow Balance: Old vs. NewGOF Portion of Dune Sand Aquifer

LGFM 2.0 LGFM 3.0FlowComponent gpm Percent gpm Percent

Lateralinflow

194 24.2 83 12.3

Lateraloutflow

709 88.1 593 87.3

Rechargeinflow

565 70.3 565 83.3

ET outflow 77 9.6 63 9.2

Inflowthroughbottom

44 5.5 30 4.4

Outflowthroughbottom

18 2.2 23 3.4

Total 804 100 678 100

Dune SandAquifer

Whole ModelSubregion

Within DuneSand Aquifer

All LayersWithin

Subregion

Type Percent Change Percent Change Percent Change Percent Change

Lateral inflow -84 6 -57 1

Lateral outflow -13 2 -16 2

Willows outflow No willowspresent

0 No willowspresent

No willowspresent

Inflow fromriver

No river present 33 No river present No river present

Outflow to river No river present -61 No river present No river present

Drain outflow No drain present Added inLGFM 3.0

No drain present No drain present

Recharge inflow -1 -40 0 0

ET outflow -45 -45 -18 -18

Inflow throughbottom

22 0 -32 0

Outflow throughbottom

-22 0 28 0

Net OverallChange

-23 -15 -16 1

Flow Balance: Old vs. New

Conclusions

• Model is more realistic in several ways:– layer structure– drain and river– agricultural fields– water balance

• Complies better with conceptual model

Conclusions

• Model represents shared vision

• Will provide better predictions of groundwater flow for future characterization and remediation issues