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53'%/,/')#!,3526%9 7ATER 2ESOURCES)NVESTIGATIONS2EPORT  6ERSION !UGUST Estimating Ground-Water Recharge from Precipitation on Whidbey and Camano Islands, Island County, Washington, Water Years 1998 and 1999

By S. S. Sumioka and H. H. Bauer

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 03-4101 Version Number 1.20, August 2004

Prepared in cooperation with the

ISLAND COUNTY HEALTH DEPARTMENT

Tacoma, Washington 2003 U.S. DEPARTMENT OF THE INTERIOR GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY Charles G. Groat, Director

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government.

For additional information write to: Copies of this report can be purchased from:

Director, Washington Water Science Center U.S. Geological Survey U.S. Geological Survey Information Services 1201 Pacific Avenue – Suite 600 Building 810 Tacoma, Washington 98402 Box 25286, Federal Center http://wa.water.usgs.gov Denver, CO 80225-0286 CONTENTS

Abstract ...... 1 Introduction ...... 1 Purpose and Scope ...... 3 Previous Studies...... 3 Well-Numbering System...... 3 Acknowledgments...... 3 Description of Study Area...... 5 Description of Study Basins...... 5 Climate and Precipitation...... 6 Hydrogeology...... 6 Recharge, Evapotranspiration, and Discharge ...... 9 Estimates of Ground-Water Recharge...... 9 Near-Surface Water-Balance Method...... 10 Data Collection and Processing ...... 11 Precipitation ...... 13 Precipitation Throughfall...... 13 Streamflow...... 13 Shortwave Solar Radiation and Temperature ...... 18 Soil and Subsoil Properties ...... 18 Land Cover and Vegetation ...... 20 Land Surface ...... 20 Other Data...... 22 Model Adjustment...... 22 Island-Wide Recharge Estimates for Whidbey and Camano Islands Using the Deep Percolation Model...... 23 Sources of Uncertainty in DPM Recharge Estimates ...... 26 Chloride Mass-Balance Method...... 27 Data Collection ...... 28 Recharge Estimates and Sources of Uncertainty Using Chloride Mass-Balance Method...... 29 Summary ...... 31 References Cited ...... 32 Appendix A.Monthly computer water-budget summaries for the six study basins...... 34 Appendix B. Monthly computer water-budget summaries for Whidbey and Camano Islands...... 46

Contents iii FIGURES

Figure 1. Map showing locations of six study basins on Whidbey and Camano Islands, Island County, Washington...... 2 Figure 2. Diagram showing well-numbering system used in Washington ...... 4 Figure 3. Map showing average annual precipitation on Whidbey and Camano Islands, Island County, Washington...... 7 Figure 4. Map showing generalized surficial geology of Whidbey and Camano Islands, Island County, Washington...... 8 Figure 5. Graphs showing precipitation for the six study basins on Whidbey and Camano Islands, Island County, Washington, water years 1998-99...... 14 Figure 6. Graphs showing daily mean stream discharges for the six study basins on Whidbey and Camano Islands, Island County, Washington, water years 1998-99...... 16 Figure 7. Map showing generalized soil groupings of Island County soil series for Whidbey and Camano Islands, Island County, Washington ...... 19 Figure 8. Map showing distribution of land cover reclassified for the Deep Percolation Model for Whidbey and Camano Islands, Island County, Washington...... 21 Figure 9. Map showing distribution of average annual recharge simulated by the Deep Percolation Model, Island County, Washington ...... 25

iv Figures TABLES

Table 1. Selected basin characteristics of the six study basins on Whidbey and Camano Islands, Island County, Washington, water years 1998-99...... 5 Table 2. Predominant soil types used in the Deep Percolation Model to determine recharge from precipitation for the six study basins on Whidbey and Camano Islands, Island County, Washington...... 12 Table 3. Land-cover categories used in the Deep Percolation Model for the six study basins on Whidbey and Camano Islands, Island County, Washington ...... 12 Table 4. Grid dimensions for modeled basins and Whidbey and Camano Islands, Island County, Washington...... 13 Table 5. Summary of streamflow data for the six study basins on Whidbey and Camano Islands, Island County, Washington, water years 1998-99...... 18 Table 6. Reclassification of land-cover data to categories used by the Deep Percolation Model for Whidbey and Camano Islands, Island County, Washington...... 20 Table 7. Land-cover categories used in the Deep Percolation Model (DPM) for Whidbey and Camano Islands, Island County, Washington...... 23 Table 8. Soil groups composited for the Deep Percolation Model using Island County soil series for Whidbey and Camano Islands, Island County, Washington...... 24 Table 9. Summary of chloride in precipitation and dry-atmospheric deposition measured at two locations on Whidbey Island, Island County, Washington, May 1998 through April 1999 ...... 29 Table 10. Summary of selected physical characteristics and chloride concentrations for wells used in the chloride-mass balance, Whidbey Island, Island County, Washington, water years 1998-99...... 30

Tables v CONVERSION FACTORS AND DATUM

CONVERSION FACTORS

Multiply By To obtain acre 4,047 square meter acre 0.4047 hectare cubic foot per second (ft3/s) 0.02832 cubic meter per second foot (ft) 0.3048 meter foot per day (ft/d) 0.3048 meter per day inch (in.) 25.4 millimeters inch per day (in/d) 25.4 millimeter per day inch per year 25.4 millimeter per year inch per inch 25.4 millimeter per inch mile (mi) 1.609 kilometer square mile (mi2) 2.590 square kilometer

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows: °F= (1.8 × °C)+32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows: °C= (°F-32)/1.8

Concentrations of chemical constituents in water are given in milligrams per liter. One milligram per liter is equivalent to one thousand micrograms per liter. One microgram per liter is equivalent to “parts per billion.”

The flux of chemical constituents in atmospheric deposition is expressed as milligrams per square meter (mg/m2). For example, the flux, in milligrams per square meter per year [(mg/m2)/yr], can be multiplied by the precipitation in millimeters per year (mm/yr) to obtain the concentrations in milligrams per liter of a constituent in wet or dry deposition.

DATUM

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 (NGVD of 1929).

vi Conversion Factors and Datum Estimating Ground-Water Recharge from Precipitation on Whidbey and Camano Islands, Island County, Washington, for Water Years 1998 and 1999

By S. S. Sumioka and H. H. Bauer

ABSTRACT selected wells indicates that the average recharge to unconsolidated deposits ranges from 0.78 to Ground-water recharge from precipitation to 7.81 inches per year. Sources of chloride in ground unconsolidated deposits on Whidbey and Camano water other than from the atmosphere would cause Islands, Washington, was estimated for water recharge estimated by the chloride mass-balance years 1998-99 using a near-surface water-balance method to be less than the actual recharge, method and a chloride mass-balance method. therefore, these estimates may represent lower A daily near-surface water-balance method, limits. the Deep Percolation Model (DPM), was used to simulate water budgets for October 1, 1997 through September 30, 1999 (water years 1998- INTRODUCTION 99) for six small drainage basins—four on Whidbey Island and two on Camano Island. The principal source of drinking water on Adjusted parameters from the DPM for each small Whidbey and Camano Islands, located off the basin were then used in island-wide DPM northwestern coast of Washington (fig. 1), is ground simulations. A spatial distribution of annual water derived from unconsolidated glacial- and interglacial-deposit aquifers. Some uncertainty exists recharge was simulated for each island, with island regarding the quantity of recharge from precipitation averages of 5.71 inches per year for Whidbey reaching the aquifers used for water supply. Island and 5.98 inches per year for Camano Island. In 1997, the U.S. Geological Survey (USGS), in The spatial distribution of simulated annual cooperation with the Island County Health Department, recharge for each island reflects variations in began a study to estimate recharge from precipitation to precipitation amounts and the distribution of unconsolidated glacial- and interglacial-deposit surficial materials. DPM results indicate that aquifers on Whidbey and Camano Islands. Indirect recharge generally is higher in areas underlain by recharge estimates can be subject to large errors, and coarse-grained deposits (outwash) than in areas therefore, when possible, more than one method should underlain by fine-grained deposits (till). be used to verify the estimates. A commonly used A chloride mass-balance method was used indirect method equates ground-water recharge to to estimate combined recharge to unconsolidated measured ground-water discharge. However, much of deposits on Whidbey and Camano Islands. The the ground water in Island County probably discharges through the seabed, and this method cannot be used average combined recharge for Whidbey and (Sapik and others, 1988). Therefore, two indirect Camano Islands estimated by this method was methods were used: a near-surface water-balance 2.00 inches per year. The range of chloride method and a chloride mass-balance method. concentrations in ground-water samples from

Introduction 1 — —v

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Figure 1. Locations of six study basins on Whidbey and Camano Islands, Island County, Washington.

2 Estimating Ground-Water Recharge from Precipitation on Whidbey and Camano Islands, Island County, Washington, for Water Years 1998 and 1999 Purpose and Scope Cline and others (1982) summarized existing data regarding ground-water resources of Island The purpose of this report is to present the results County and identified areas where overpumping was of a study to (1) estimate ground-water recharge from evident or appeared imminent. In addition, water levels precipitation to unconsolidated glacial- and and chloride concentrations in wells were collected to interglacial-deposit aquifers in six study basins on identify existing and potential areas of seawater Whidbey and Camano Islands for water years 1998-99 intrusion. Recharge for Island County was determined using a near-surface water-balance method and a using a finite-difference model to simulate the position chloride mass-balance method; (2) use the ground- of the freshwater-seawater interface and was estimated water recharge estimates from the chloride mass- to be 4.9 inches per year. balance method to assess the reasonableness of Sapik and others (1988) also summarized the estimates from the water-balance method; and (3) geohydrology of Island County, and constructed a simulate ground-water recharge for the entire areas of calibrated three-dimensional ground-water flow model Whidbey and Camano Islands for water years 1998-99 to simulate the flow of fresh ground water in a using recharge estimates from the near-surface water- multiple-layered aquifer system containing freshwater balance method for the six study basins. and seawater, separated by a sharp interface. Recharge The near-surface water-balance was simulated on for Island County was simulated using a daily soil- a daily basis using the Deep Percolation Model (DPM) moisture accounting method and was estimated to be (Bauer and Vaccaro, 1987; Bauer and Mastin, 1997) to 12 inches per year. estimate ground-water recharge. Annual ground-water recharge also was estimated using the chloride mass- balance method (Eriksson and Khunakasem, 1969). Well-Numbering System Data required to apply these methods were obtained from existing databases and collected as part of this The well-numbering system used by the USGS study. Geographic information system programs in the State of Washington is based on the rectangular (ARC/INFO and ARC/GRID) were used to enter study subdivision of public land, and indicates township, basin data into the DPM. range, section, and 40-acre tract within the section Data collected during water years 1998-99 (fig. 2). For example, in well number 28N/03E-10L02, included streamflow, precipitation, precipitation the part preceding the hyphen indicates the township throughfall, shortwave solar radiation, air temperature, and range (Township 28 North, Range 3 East). The first and atmospheric-chloride deposition (in precipitation number following the hyphen (10) indicates the section and as dry deposition). Chloride concentrations in number, and the letter (L) gives the 40-acre tract within ground water were determined from samples collected that section. The last number (02) is the sequence at selected wells located throughout the study area in number of the well in that 40-acre tract. the autumn of 2000. Additional data (geology, soil properties, topography, and land cover) were obtained from existing databases. Acknowledgments Appreciation is expressed to all landowners who Previous Studies gave their permission to establish streamflow-gaging stations and meteorological sites on their property. Anderson (1968) described the location and Acknowledgment also is given to well owners who availability of ground water in Island County as well as gave their permission to sample their wells to obtain the geographic and hydrologic setting of the county data for the chloride mass-balance calculations. and the areal and vertical extent of ground water. In the descriptions of the hydrologic cycle in Island County, only a few general statements were made pertaining to ground-water recharge.

Introduction 3 Study area

W A S H I N G T O N

Willamette Meridian

Willamette Base Line

6 5 4 3 2 1 D C B A T. 712EFG H 18 13 M L K J 28N/03E-10L02 28 19 24 NPQR

N. 30 25 SECTION 10

31 32 33 34 35 36 R. 03 E.

Explanation Well-Numbering System

The USGS assigns numbers to wells and springs in Washington that identify their location in a township, range, and section. Well number 28N/03E-10L02 indicates successively, the township (T. 28 N) and range (R. 03 E) north and east of the Willamette Base Line and Meridian. The first number following the hyphen indicates the section (10) within the township, and the letter following the section number gives the 40-acre subdivision of the section, as shown above. The number (02) following the letter is the sequence number of the well within the 40-acre subdivision. This number indicates that the well was the second one inventoried by USGS personnel in that 40-acre tract. An "S" following the sequence number indicates that the site is a spring; a "D1" after the sequence number indicates that the original reported depth of the well has been changed once, and successive numbers indicate the number of changes in well depth.

Figure 2. Well-numbering system used in Washington.

4 Estimating Ground-Water Recharge from Precipitation on Whidbey and Camano Islands, Island County, Washington, for Water Years 1998 and 1999 DESCRIPTION OF STUDY AREA covers in Island County (fig. 1). The principal characteristics of each drainage basin and the USGS The two major islands of Island County occupy stream-gaging station numbers in the USGS database an area of about 210 square miles off the coast of are shown in table 1. northwestern Washington State (fig. 1). The larger of Two of the basins are drained by perennial the islands, Whidbey, has an area of about streams, the others are drained by intermittent streams. 168 square miles and Camano Island has an area of Streamflow-gaging stations were established in each of about 39 square miles. Land surface on both islands the six basins and equipped with data loggers. For this consists of rolling uplands, ranging in altitude from sea report, basins will be referred to by the USGS gaging level to about 600 feet above sea level. station number. Gaging station 12170305 is located on an intermittent stream draining into Saratoga Passage, on Description of Study Basins the west side of southern Camano Island. The contributing drainage area for this gaging station is Six small basins, four on Whidbey Island and 0.27 square mile. Land cover in the basin consists of two on Camano Island, were selected following field coniferous forest with small areas of grassland. The reconnaissance to represent common flow regimes, basin is underlain by coarse to fine-grained precipitation, surficial material characteristics, and land unconsolidated deposits.

Table 1. Selected basin characteristics of the six study basins on Whidbey and Camano Islands, Island County, Washington, water years 1998-99

[DPM, Deep Percolation Model]

Precipitation Contributing Geologic Predominant (inches per year) Gaging Predominant Basin drainage area material DPM land Long-term station No. soil type Water year Water year (square miles) underlying soil cover average 1998 1999 annual

Southern Camano 0.27 12170305 Alderwood Coarse to fine- Coniferous 27.7 28.9 33.9 Island grained forest unconsolidated deposits

Northern Camano 0.42 12170310 Bow Coarse to fine- Coniferous 22.8 24.8 28.2 Island grained forest unconsolidated deposits

Northern Whidbey 1.6 12170315 Whidbey Fine-grained Coniferous 24.5 25.3 31.1 Island unconsolidated forest deposits

Penn Cove, northern 0.97 12170320 Swantown Fine-grained Grassland 16.6 17.8 22.7 Whidbey Island unconsolidated deposits

Cultus Creek, 1.5 12170400 Whidbey Fine-grained Coniferous 29.4 29.3 37.0 southern Whidbey unconsolidated forest Island deposits

South Whidbey State 0.13 12170440 Whidbey Fine-grained Coniferous 25.0 26.0 31.5 Park, Whidbey unconsolidated forest Island deposits

Description of Study Area 5 Station 12170310 is located on an intermittent Climate and Precipitation stream on northern Camano Island. The natural drainage pattern for this basin is disrupted by a Island County has a temperate, marine climate roadside ditch that channels runoff to Puget Sound. The with dry summers and wet winters. Average annual contributing drainage area for the gaging station is 0.42 maximum temperature for 1984-2000 was 57.9 oF at square mile. Land cover in the basin consists of Coupeville on Whidbey Island; average annual coniferous forest. The basin is underlain by coarse to minimum temperature for the same period was 41.7 °F. fine-grained unconsolidated deposits. July typically is the warmest month, with an average Station 12170315 is located on a perennial maximum temperature of 71.3 °F and January is the stream on the northern end of Whidbey Island near coldest month, with a long-term average minimum Skagit Bay. The contributing drainage area for the temperature of 50.3 oF (Western Region Climate gaging station is 1.63 square miles. Land cover in the Center, 2001). basin consists of coniferous forest and grass and Data from PRISM (Precipitation-Elevation cropland. This basin is underlain by fine-grained Regression on Independent Slopes Model; Daly and unconsolidated deposits. others, 1994) indicate that average annual precipitation Station 12170320 is located on an intermittent from 1961 to 1990 ranged from 35 inches on southern stream in north-central Whidbey Island on the northern Whidbey Island to 29 inches on northern Whidbey side of Penn Cove. The contributing drainage area for Island, and from 25 inches on western Camano Island the gage is 0.97 square mile. Land cover in this basin to about 31 inches on the northern part of Camano consists of grassland, coniferous forest, and some Island nearest the mainland (fig. 3). Some areas of cropland. This basin is underlain by fine-grained Island County are influenced by the rainshadow effect unconsolidated deposits. of the Olympic Mountains, about 50 miles southwest of Station 12170400 is located on Cultus Creek, a Island County. The central part of Whidbey Island perennial stream on southern Whidbey Island. The receives fewer than 23 inches of average annual contributing drainage area for the gaging station is 1.5 precipitation. square miles. Land cover in this basin consists primarily of coniferous forest. The basin is underlain by fine-grained unconsolidated material. Hydrogeology Station 12170440 is located on an unnamed Unconsolidated Quaternary-age glacial and stream on the west side of Whidbey Island, and drains interglacial deposits overlie Tertiary- to Jurassic-age into Admiralty Inlet. The contributing drainage area for bedrock (fig. 4) throughout most of Whidbey and the gaging station is 0.13 square mile. Land cover Camano Islands (Easterbrook, 1968; Cline and others, consists entirely of coniferous forest. The basin is 1982). Bedrock exposures are limited to the Deception underlain by fine-grained unconsolidated deposits. Pass area at the northern end of Whidbey Island Data also were collected at other sites on the two (fig. 1), and the low tidal zone at Rocky Point, 5 miles islands outside the study basins. Two temporary to the south. Unconsolidated deposits consist of clay, micrometeorological sites that measured solar radiation silt, sand, and gravel, and range in thickness from a few and air temperature were installed, one on northern hundred feet to about 3,000 feet in the central part of Whidbey Island overlooking Penn Cove and one on Whidbey Island (Cline and others, 1982; Pessel and southern Whidbey Island near the gaging station on others, 1989; Yount and others, 1993). Bedrock in the Cultus Creek (station 12170400). Atmospheric study area consists of sedimentary and deposition data were collected at one site on each metasedimentary units of marine origin, and volcanic island: on northern Whidbey Island near gaging station rock (Cline and others, 1982; Whetten and others, 12170315 and on the east side of southern Camano 1988; Yount and Gower, 1991). Island near gaging station 12170305 (the micrometeorological site was assigned the same number as the gaging station).

6 Estimating Ground-Water Recharge from Precipitation on Whidbey and Camano Islands, Island County, Washington, for Water Years 1998 and 1999 122°45' 122°22'30"

0 24 6 MILES

0 24 6 KILOMETERS 48° 22' 30" T 33 N

S kagit Bay

STRAIT OF JUAN DE FUCA

CAMANO Penn Cove ISLAND

WHIDBEY S a r ISLAND atoga Passage Port T Susan 31 Admi N ralty Inlet

EXPLANATION AVERAGE ANNUAL PRECIPITATION, IN INCHES

21 - 22.9 23 - 24.9

25 - 26.9 T 48° 27-28.9 29 29 - 30.9 N 31 - 32.9 33 - 34.9

35 - 36.9 BOUNDARY OF DRAINAGEBASIN BOUNDARY OF STUDY AREA

Base modified from U.S. Geological Survey R.1 E. R.3 E. digital data, 1:2,000,000, 1972 Universal Transverse Mercator projection, Zone 10

Figure 3. Average annual precipitation on Whidbey and Camano Islands, Island County, Washington. Precipitation values are from gridded values from PRISM (Oregon Climate Services, 1999) for 1961-90.

Description of Study Area 7 122°45' 122°22'30"

0 24 6 MILES

0 24 6 KILOMETERS 48° 22' 30" T 33 N

S kagit Bay

STRAIT OF JUAN DE FUCA

Penn Cove CAMANO ISLAND WHIDBEY S a r ISLAND atoga Passage Port T Susan 31 Admi N ralty Inlet

EXPLANATION SURFICIAL GEOLOGY Alluvial deposits

Fine-grained unconsolidated deposits Coarse-grained T unconsolidated 29 48° deposits N Bedrock

No data

BOUNDARY OF DRAINAGEBASIN BOUNDARY OF STUDY AREA

Base modified from U.S. Geological Survey R.1 E. R.3 E. digital data, 1:2,000,000, 1972 Universal Transverse Mercator projection, Zone 10

Figure 4. Generalized surficial geology of Whidbey and Camano Islands, Island County, Washington.

8 Estimating Ground-Water Recharge from Precipitation on Whidbey and Camano Islands, Island County, Washington, for Water Years 1998 and 1999 Most wells in the county (about 70 percent) are Washington because portions of the county are in the 200 feet or less in depth and obtain water from rainshadow of the Olympic Mountains and receive less unconsolidated sand and gravel deposits at depths of a precipitation. few tens of feet above sea level to about 200 feet below If soil-moisture holding capacities and root-zone sea level (locally known as the sea-level aquifer). More depths are sufficiently large, recharge (rainwater not than 90 percent are less than 300 feet deep. Most of the evapotranspired) could, in places, be nearly zero. deeper wells (greater than 300 feet) are public-supply Additionally, results from recent USGS studies in wells serving the cities and housing developments in coniferous forested areas in the Puget Sound Lowland the county. The sea-level aquifer is both confined and of western Washington have shown that measured daily unconfined over its extent (Sapik and others, 1988). evaporation frequently exceeds daily PET (potential Deposits in the sea-level aquifer appear to be more evapotranspiration) computed by traditional methods. continuous than similar deposits at shallower depths Large amounts of advective evaporation by vegetation relative to land surface (Cline and others, 1982). Sand of intercepted precipitation (as much as 10 to 18 inches and gravel water-bearing deposits above the sea-level annually) are not accounted for in the traditional aquifer occur primarily in northeastern and methods (Bauer and Mastin, 1997; Bidlake and Payne, southeastern Whidbey Island and likely are of limited 2001). The quantity of recharge in these areas could be vertical and areal extent. Sand and gravel water-bearing less than would be expected. deposits below the sea-level aquifer are not widely Under natural conditions, ground-water recharge used as a source of water and little is known about the in Island County is in approximate balance with extent or hydraulic properties of these deeper deposits. ground-water discharge to the ocean, to gaining Bedrock in Island County generally yields little or no reaches of streams, and to plant transpiration in areas of water to wells (Cline and others, 1982). shallow water table. Withdrawals from wells and resultant ground-water level declines may decrease outflow to natural discharge areas and increase Recharge, Evapotranspiration, and Discharge seawater intrusion of freshwater aquifers. Withdrawals also may decrease baseflow to streams leading to Direct recharge to ground water from degradation of wildlife habitat. Most of the water precipitation (deep percolation) results from the pumped from wells in Island County is used for infiltration of precipitation through the soil horizon and household purposes, with irrigation, commercial, and below the root zone to the water table. Factors industrial uses accounting for the remainder. controlling recharge from precipitation include storm duration and intensity, land cover, soil characteristics, and thickness of the unsaturated zone. Factors that ESTIMATES OF GROUND-WATER control evapotranspiration (air temperature, shortwave solar radiation, wind speed, soil type, vegetation type, RECHARGE and land-surface slope) also affect rates of deep percolation. Deep percolation in many areas may be Ground-water recharge cannot be measured further limited by low-permeability materials directly and is difficult to accurately estimate. Indirect underlying soils. For a period of time during and recharge estimates can be subject to large errors and following a storm, rainwater infiltrating the soil that therefore, when possible, more than one method should encounters low-permeability glacial till may move be used to verify the estimates. A common indirect short distances horizontally, to local drainages that method for hydrologic systems under equilibrium discharge directly to the ocean and thus, is not available conditions is to equate ground-water recharge to for recharging the ground-water system (Anderson, ground-water discharge. However, much of the ground 1968). The collection of detailed streamflow data was water in Island County probably discharges through the therefore an essential component of data-collection seabed, and this method cannot be used because the activities for this study to estimate these direct equilibrium equation, in this case, has two unknown discharges to the ocean. Deep percolation in Island quantities, ground-water discharge directly to the sea County probably is less than in most of western and recharge. Therefore, two other indirect methods were used: a near-surface water-balance method and a chloride mass-balance method.

Estimates of Ground-Water Recharge 9 Near-Surface Water-Balance Method defined as surface-water runoff plus water that drains from partially saturated soil to local drainage features. The primary method for estimating recharge Areal variation in soils, vegetation, and land cover are from precipitation for this study was the near-surface accounted for in the DPM by dividing a drainage area water-balance model. The DPM, developed for eastern into a number of cells of any size or shape such that Washington (Bauer and Vaccaro, 1987) and modified each cell represents a single altitude, land cover, soil for western Washington (Bauer and Mastin, 1997), was type, and climate regime. Areal variation in selected to estimate recharge from precipitation for this precipitation, temperature, and solar radiation were study. The DPM uses a daily water-budget approach to accounted for by using precipitation recorder stations estimate recharge. For each cell, the following equation spread within and (or) near the study basin and the two is solved, daily, for a column extending from the micrometeorological sites. vegetation covering the land surface down to the Soil moisture is accounted for, daily, by adding bottom of the root zone. surplus water (precipitation plus snowmelt minus sublimation minus interception minus surface runoff) RECHRG = PRECIP - EVINT - EVSOL to the soil. Water is then removed by transpiration and - EVSNW - TR - RO - CHGINT soil evaporation. Surplus water is added to the soil- - CHGSNW - CHGSM, (1) moisture reservoir layer by layer, using 6-inch layers for each soil. If the surplus is less than the difference where between the available water capacity (field capacity RECHRG is water percolating to below the root minus the wilting point) and the current soil-moisture zone (recharge); content, the current moisture content is increased by PRECIP is precipitation; the surplus. If the surplus is greater than the difference, the water content of the soil is brought to available EVINT is evaporation of moisture intercepted water capacity and the remaining surplus is passed by foliage (interception loss); down to the next layer. This process continues until EVSOL is evaporation from bare soil; there is no more surplus water or until all layers are EVSNW is sublimation; filled. Any surplus after all layers are at field capacity TR is transpiration; is deep percolation. RO is direct runoff; The initial soil-moisture content was estimated CHGINT is change in moisture stored on foliage; to be a fraction of field capacity. This fraction was CHGSNW is change in snowpack; and arrived at by evaluating precipitation prior to the simulation period and selecting an appropriate estimate CHGSM is change in soil water in the root zone. based on the thickness of the soil and the available In this method, the model simulates daily fluxes water capacity. of water into and out of a column extending from the Evapotranspiration depends on soil-moisture top of foliage to the bottom of the root zone and availability as well as on meteorological conditions and accounts for changes in water content. Ground-water their effects on vegetation. Evapotranspiration depletes recharge is assumed to equal the water moving soil moisture and shallow ground water; therefore, vertically downward from the bottom of the root zone evapotranspiration and soil moisture must be calculated (deep percolation). at sufficiently frequent intervals. The DPM uses a daily Data required for the DPM include daily values time step, primarily because daily meteorological data of precipitation, precipitation throughfall (rain that generally are available. A daily time step is sufficiently reaches land surface beneath vegetation), air short to assure that soil-moisture variations are small temperature, shortwave solar radiation, land-surface enough to avoid significant error in the altitude, and properties of soils and land cover evapotranspiration calculations. (vegetation type, surface water, or impervious surfaces), and "direct runoff." Direct runoff is herein

10 Estimating Ground-Water Recharge from Precipitation on Whidbey and Camano Islands, Island County, Washington, for Water Years 1998 and 1999 For each day of a DPM simulation, deep Data Collection and Processing percolation for each cell is computed as precipitation In step 1 of the process, each of the six study minus evapotranspiration minus direct runoff minus the basins was divided into a uniform grid of cells, each 30 change in soil moisture in the root zone. Precipitation meters (98.45 feet) on a side and with an area of 900 and the other weather variables from which square meters (0.222 acre). The 30-meter cell size was evapotranspiration is computed are determined for selected to match the 30-meter resolution of the land- each cell by simple distance extrapolation from the cover data, which was the highest resolution of all the data-collection sites. Direct runoff for each cell is much coverages used. Each cell was assigned the more difficult to estimate. Although the total direct predominant soil type and land use that occurred in the runoff for a drainage basin (total of all cells) can be cell (tables 2 and 3). When the island-wide models readily estimated from the stream-discharge were run, cell size was increased in order to measurements, the contributions from individual cells accommodate file-size limitations in pre- and post- can vary greatly depending on the soil and subsoil processing software. Increasing the cell size of a model properties. For example, during a storm, a cell with a may likely lead to a loss of resolution in model results, thick soil underlain by a permeable glacial-outwash but a similar cell size was used for a recharge study of deposit (sand and gravel) may not contribute to direct the Sequim-Dungeness area of Clallam County, runoff, whereas a cell with thin soil overlying poorly Washington with good results (Thomas and others, permeable glacial till will produce a large quantity of 1999). The cell sizes for island-wide modeling was direct runoff. The DPM disaggregates the total direct increased to a uniform grid of cells 210 meters (689 runoff to the cells in proportion to a calculated or feet) on a side and an area of about 44,000 square theoretical direct runoff for each cell (for details, see meters (about 11 acres). General characteristics of the Bauer and Mastin, 1997). A specified infiltration modeled basins and islands are shown in table 4. capacity for each cell, based on soils and subsoil Daily values of precipitation, precipitation properties, is incorporated into these calculations. By throughfall, shortwave solar radiation, air temperature, adjusting this parameter, a water balance is achieved and stream-discharge data collected by the USGS for the modeled area. If the infiltration capacity is set during water years 1998-99 were used in the model too large, too little water will be available to support simulations. Most properties of soils, vegetation, and the measured total direct runoff. This is indicated as a land cover were obtained from previous studies of "negative” soil-saturation deficit in the DPM output Island County. DPM model parameters defining (DEFICIT); conversely, a positive soil-saturation maximum clear-sky solar shortwave radiation, non- deficit results when the infiltration capacities are set plant factors affecting transpiration, and snowmelt and too small. sublimation were compiled from values used in two Three steps were used to estimate recharge using previous applications of the DPM to areas of western the near-surface water-balance method in this study: Washington. Bauer and Mastin (1997) estimated (1) all data needed for applying the DPM to the study recharge in till-covered areas and Bidlake and Payne area were assembled, checked for accuracy, and (2001) estimated recharge in areas covered by till and divided into uniform cells (a process known as glacial outwash. These two studies used locally "gridding"); (2) the DPM was adjusted for each of the measured meteorological and hydrologic data, six study basins; and (3) the DPM was applied to the including direct stream runoff, soil-water content, and entire island using results of the study basin ground-water levels. Parameter values from these simulations. Island-wide direct runoff data were not previous two studies were used in this study because all available, therefore, DPM simulations in step 3 used three study areas have similar climate, vegetation, simulated direct runoff in place of disaggregated geology, and topography. measured runoff.

Estimates of Ground-Water Recharge 11 Table 2. Predominant soil types used in the Deep Percolation Model to determine recharge from precipitation for the six study basins on Whidbey and Camano Islands, Island County, Washington

[Area: Percent, percentage of total basin area. Percentages do not always equal 100 percent because of rounding. –, no data]

Whidbey Island Camano Island 12170315 12170320 12170400 12170440 12170305 12170310 Soil series Area Square Square Square Square Square Square Percent Percent Percent Percent Percent Percent miles miles miles miles miles miles

Alderwood – – – – – – – – 0.22 80.65 0.02 4.42 Bellingham 0.02 1.17 0.01 1.12 – – – – – – .02 3.94 Bow – – – – – – – – – – .38 91.17 Casey – – .20 21.08 – – – – – – – – Coveland – – .10 10.25 – – – – – – – – Everett – – – – – – – – – – .002 .47 Hoypus .09 5.77 .03 2.71 0.01 0.69 – – – – – – Indianola – – – – – – – – .04 13.00 – – Keystone .03 1.72 – – .29 19.25 – – – – – – Norma .07 4.50 .03 3.16 .06 4.11 – – .02 5.47 – – Rifle – – – – .02 1.55 – – – – – – Rough, broken land – – – – – – – – .000 .004 – – Semiahmoo .01 .89 .003 .27 – – – – – – – – Swantown .005 .29 .30 30.65 – – – – – – – – Tanwax .003 .21 – – .01 .76 – – .002 .88 – – Townsend – – .17 17.11 – – – – – – – – Whidbey 1.39 85.46 .13 13.66 1.11 73.64 0.13 100.00 – – – –

Table 3. Land-cover categories used in the Deep Percolation Model for the six study basins on Whidbey and Camano Islands, Island County, Washington

[Area: Percent, percentage of total basin area. Percentages do not always equal 100 percent because of rounding. –, no data]

Whidbey Island Camano Island 12170315 12170320 12170400 12170440 12170305 12170310 Land cover Area Square Square Square Square Square Square Percent Percent Percent Percent Percent Percent miles miles miles miles miles miles

Coniferous forest 1.44 88.16 0.29 29.90 1.5 94.12 0.13 100.00 0.25 91.67 0.34 81.60

Grass .08 4.93 .58 59.62 .09 5.88 – – .02 8.33 – –

Alfalfa .11 6.92 .10 10.21 – – – – – – .08 18.40

Open water – – .003 0.27 – – – – – – – – Total 1.63 – 0.97 – 1.5 – 0.13 – 0.27 – 0.42 –

12 Estimating Ground-Water Recharge from Precipitation on Whidbey and Camano Islands, Island County, Washington, for Water Years 1998 and 1999 Table 4. Grid dimensions for modeled basins and Whidbey and Camano Seven storage type precipitation gages were installed at Islands, Island County, Washington each site, placed randomly under the leaf cover. One precipitation gage was placed in an adjacent open area [DPM, Deep Percolation Model. Percentages do not always equal 100 percent because of rounding and may not agree exactly with similar as a control. Rainfall was measured monthly. percentages in other tables in this report] Throughfall, as a percentage of precipitation, was calculated for the periods between measurements as the Cell size used Modeled area Number of average of the leaf-cover gage precipitation divided by Basin/Island for DPM (square cells the precipitation measured in the gage in the open area. (meters) miles) Because measurement times were variable, a 12170305 30 × 30 792 0.27 consistent basis was required to produce 24-hour 12170310 30 × 30 1,206 .42 values of throughfall for each site. This was done by 12170315 30 × 30 4,704 1.6 calculating the average throughfall as a fraction of 12170320 30 × 30 2,794 .95 precipitation for each rainy period, separated by non- 12170400 30 × 30 4,351 1.45 precipitation periods of 1 or more days. For each site, 12170440 30 × 30 366 .13 the throughfall fraction for each rainy period was then Whidbey Island 210 × 210 9,840 167.5 assumed to be the same for each of the days during the Camano Island 210 × 210 2,294 39.1 wet period.

Precipitation Streamflow Six continuous recording tipping-bucket Gage height was measured during water years precipitation gages were installed at locations near 1998-99 at gaging stations established at the upstream gaging stations established for this study—four on opening of pre-existing stream culverts in each of the Whidbey Island and two on Camano Island—and data six study basins. Instantaneous discharge was were collected during water years 1998-99 (fig. 5). measured monthly on each stream to construct a gage- Precipitation gages were connected to data loggers. height/discharge relation for a range of flows. Gage Each bucket tip, representing 0.01 inch of precipitation, height was recorded every 15 minutes and averaged was counted and the total amounts recorded in the data and stored as daily mean gage height. The gage logger at 60-minute intervals. Data were retrieved from height/discharge relation was used to convert daily the data loggers at about 1-month intervals. mean gage height to daily mean discharge (fig. 6). Two of the tipping bucket gages on the northern During data collection, stage recorders or data and southern ends of Whidbey Island were set up as loggers sometimes malfunctioned, leading to the loss part of two temporary micrometeorological sites that of stage records. Daily mean discharge for periods of also collected temperature and shortwave solar missing record were estimated using a regression radiation (see section "Shortwave Solar Radiation and equation developed using data from gaging stations in Temperature"). the other study basins and data from Huge and Big Beef Creeks in Kitsap and Pierce Counties about 50 Precipitation Throughfall miles southwest of Island County. The streamflow data are summarized in table 5. Streamflow derived from Evaporation of precipitation temporarily stored ground-water discharge into a stream (baseflow) was on the foliage in forested areas proceeds at estimated from the total-flow hydrograph based on the considerably faster rates than transpiration, especially assumption that total streamflow is equal to baseflow during the winter months, and annually can be as much during summer months when precipitation is minimal as 50 percent of the total precipitation for the Puget and soils are below field capacity. A smooth baseflow Sound area (Bauer and Mastin, 1997). During this curve was drawn for dry periods and then extended investigation, throughfall (that part of precipitation not backward in time using wet-season flows from the evaporated from foliage) was measured at two sites: a total-flow hydrograph as a maximum allowable coniferous forest near gaging station 12170315 on the baseflow value. northern end of Whidbey Island and beneath a large maple tree on the southern end of Camano Island.

Estimates of Ground-Water Recharge 13 4Estimating Ground-Water Recharge from Prec 14 1.5 Station 12170305

1.0

0.5

0 1.5 ipitation onWhidbey and Cama Station 12170310 S HE C 1.0

0.5 IPITATION, IN IN IPITATION, C no Islands, Island no Islands, PRE 0 1.5 Station 12170315 County, Washington, for County, Washington, for Years Water

1.0

0.5

0 ONDJFMAMJJAS ONDJFMAMJJA S 1998and 1999 1997 1998 1999

Figure 5. Precipitation for the six study basins on Whidbey and Camano Islands, Island County, Washington, water years 1998-99. 1.5

Station 12170320 1.0

0.5

0 1.5 S HE

C Station 12170400 1.0

0.5 IPITATION, IN IN C PRE

0

1.4

1.2

Station 12170440 1.0

0.8 siae fGon-ae ehre 15 Estimates of Ground-Water Recharge 0.6

0.4

0.2

0 O N D J F M A M J J A S O N D J F M A M J J A S 1997 1998 1999

Figure 5.—Continued 6Estimating Ground-Water Recharge from Prec 16 4 Station 12170305

3

2

1 OND C

E 0 S 4 ipitation onWhidbey and Cama Station 12170310

FEET PER 3 C UBI C 2 E, IN G

HAR 1 SC no Islands, Island no Islands,

0 2.0 Station 12170315 DAILY MEAN DI County, Washington, for County, Washington, for Years Water 1.5

1.0

0.5

0 OND J FMAMJ J A S ONDJ FMAMJ JA S

1998and 1999 1997 1998 1999

Figure 6. Daily mean stream discharges for the six study basins on Whidbey and Camano Islands, Island County, Washington, water years 1998-99. 2.0 Station 12170320

1.5

1.0

0.5

0 OND C

E 15 S Station 12170400

FEET PER 10 C UBI C

E, IN 5 G HAR SC 0 1.0 Station 12170440 0.8 DAILY MEAN DI DAILY

0.6 siae fGon-ae ehre 17 Estimates of Ground-Water Recharge 0.4

0.2

0 ONDJ FMAMJ JAS ONDJ FMAMJ JA S 1997 1998 1999

Figure 6.—Continued Table 5. Summary of streamflow data for the six study basins on Whidbey and Camano Islands, Island County, Washington, water years 1998-99

Maximum Daily mean Gaging Area Total annual daily Water discharge Basin station (square discharge discharge year No. miles) (inches) Cubic feet per second

Southern Camano Island 12170305 0.27 1998 4.8 0.14 2.6 1999 5.0 .19 1.5 Northern Camano Island 12170310 .42 1998 3.5 .16 3.2 1999 3.6 .19 3.4 Northern Whidbey Island 12170315 1.6 1998 .47 .22 1.4 1999 .47 .22 1.6 Penn Cove, northern Whidbey Island 12170320 .97 1998 .47 .10 1.7 1999 .48 .13 1.8 Cultus Creek, southern Whidbey Island 12170400 1.5 1998 3.8 .85 8.8 1999 4.1 1.1 14 South Whidbey State Park, Whidbey Island 12170440 .13 1998 2.2 .08 1.1 1999 2.9 .11 .65

Shortwave Solar Radiation and Temperature soil properties for Island County and six study basins Daily incoming shortwave radiation and were obtained from the State of Washington temperature were measured during water years 1998- Department of Natural Resources Geographic 99 at the two temporary micrometeorological sites. Information System (GIS) and the Natural Resources Pyranometer and temperature probes were installed at a Conservation Service (Alan Walters, written commun., site (on southern Whidbey Island near gaging station 1997). This GIS coverage was completed in 1990, and 12170400) in a pasture 200 feet from the nearest trees. data from the coverage were checked against the soil Probes were installed at a second site on Whidbey survey of the area. Island on a bluff overlooking Penn Cove near gaging Island County soils are classified into 35 series station 12170320. The pyranometer, positioned about 5 (Alan Walters, Natural Resources Conservation feet above ground, measured incoming radiation. The Service, written commun., 1997). The 35 soil series pyranometer and temperature probes were connected were combined into 12 composite soil groups (fig. 7) along with the precipitation gage to a data logger, for the model. The soil groupings were based on which sampled output from the sensors every 15 similarities in depth, texture, vertical permeability, and minutes and recorded the average every 60 minutes. available water-holding capacity. Consideration also was given, to the extent possible, to underlying geologic material and soil texture when grouping the Soil and Subsoil Properties soils (U.S. Department of Agriculture, 1958). The soil properties used in the DPM are depth, Properties of a soil group were computed as available water-holding capacity, horizontal hydraulic area-weighted averages of the properties of the soil conductivity, specific yield, and texture. With the series in the group. Ranges of the properties for each of exception of values for hydraulic conductivities and the 12 composite soil groups were 0.04 to 0.45 inch per specific yields, soil properties were obtained from soil inch for available water-holding capacity, 0.34 to 20.0 surveys conducted by the Natural Resources feet per day for vertical hydraulic conductivity, 60 to 70 Conservation Service (U.S. Department of Agriculture, inches for soil depth. Soil texture ranged from peat to 1958). Soil information and the areal distribution of gravelly sandy loam.

18 Estimating Ground-Water Recharge from Precipitation on Whidbey and Camano Islands, Island County, Washington, for Water Years 1998 and 1999 122°45' 122°22'30"

0 24 6 MILES

0 24 6 KILOMETERS 48° 22' 30" T 33 N

S kagit Bay

STRAIT OF JUAN DE FUCA

Penn Cove

CAMANO S a ISLAND r WHIDBEY atoga Passage T ISLAND Port Susan 31 Admi N ralty Inlet

EXPLANATION SOIL GROUPS — See table 8 1

2

3

4

5

6

7

8 T 48° 29 9 N 10

11

12

BOUNDARY OF DRAINAGEBASIN BOUNDARY OF STUDY AREA

Base modified from U.S. Geological Survey R.1 E. R.3 E. digital data, 1:2,000,000, 1972 Universal Transverse Mercator projection, Zone 10

Figure 7. Generalized soil groupings of Island County soil series for Whidbey and Camano Islands, Island County, Washington.

Estimates of Ground-Water Recharge 19 Saturated vertical hydraulic conductivity of the subsoil is usually an unknown property used in the Table 6. Reclassification of land-cover data to categories used by the DPM but it is important because this parameter affects Deep Percolation Model for Whidbey and Camano Islands, Island County, Washington the downward movement of water. The values used in DPM simulations in Bauer and Mastin (1997) for till- Original classification categories Grouped land-cover covered drainage basins ranged from 4.0 to 40.0 inches for land cover categories used in DPM per year, and the values used in DPM simulations by Bidlake and Payne (2001) were 26.28 inches per year Commercial Open water for till and 876 inches per year for glacial outwash and Cropland and pasture Alfalfa other coarse-grained deposits. Vertical hydraulic Deciduous forest Orchard conductivity values used for the DPM in this study Evergreen forest Coniferous forest ranged from 2 to 200 inches per year (see section Forested wetland Grass "Model Adjustment"). Non-forested wetland Open water Herbaceous rangeland Grass Land Cover and Vegetation Mixed forest Coniferous forest Mixed rangeland Grass Land-cover information for the study area was Mixed urban Grass obtained from GIS coverages prepared by the USGS Other agricultural land Grass National Mapping Division for the Puget Sound Other urban Grass National Water-Quality Assessment program. Residential Grass Coverages were developed from Landsat Thematic Shrub/brush rangeland Shrub/brush Mapper satellite data collected at a 30-meter resolution Strip mine, quarry, or gravel pit Bare ground during the early 1990s (Vogelmann and others, 1998). Transitional area Bare ground The DPM does not accommodate all 19 categories of Transportation, communications, Bare ground land cover from the GIS data. Therefore, the GIS land- and services cover categories were grouped into DPM land-cover Water—lake Open water categories according to similarities in foliar coverage, Water—reservoir Open water root depth, and seasonal crop growth characteristics (fig. 8 and table 6; Bauer and Vaccaro, 1987). Land Surface A foliar cover value was used for all DPM land- cover categories (except surface water). Maximum root Land-surface altitude data for the study area depths were set at 5 feet for all non-agricultural were in the form of 10-meter-resolution digital (pasture/hay) and native vegetation (forest, shrubland) elevation models (DEMs) obtained from the University land covers, and 3 feet for grassland and annual crops of Washington (2000, accessed September 2000, (row crops and wheat). The 5-foot depth for non- http://wagda.lib.washington.edu/data). The DEMs were agricultural and native vegetation generally then converted at 30-meter resolution into topographic corresponds with the deepest reported soil depths of the maps using GIS. The topographic maps were checked predominant soils, the 3-foot depth for grasses is from for data reliability against USGS 7.5-minute Bauer and Mastin (1997), and the 3-foot depth for quadrangle maps of the area. annual crops is from James and others (1988).

20 Estimating Ground-Water Recharge from Precipitation on Whidbey and Camano Islands, Island County, Washington, for Water Years 1998 and 1999 122°45' 122°22'30"

0 24 6 MILES

0 24 6 KILOMETERS 48° 22' 30" T 33 N

S kagit Bay

STRAIT OF JUAN DE FUCA

Penn Cove CAMANO ISLAND S a r WHIDBEY atoga Passage Port T ISLAND Susan 31 Admi N ralty Inlet

EXPLANATION LAND COVER Shrub/Brush

Alfalfa

Bareground

Forest T Grass 48° 29 Orchard N

Wetland

Open water

No data BOUNDARY OF DRAINAGEBASIN BOUNDARY OF STUDY AREA

Base modified from U.S. Geological Survey R.1 E. R.3 E. digital data, 1:2,000,000, 1972 Universal Transverse Mercator projection, Zone 10

Figure 8. Distribution of land cover reclassified for the Deep Percolation Model for Whidbey and Camano Islands, Island County, Washington.

Estimates of Ground-Water Recharge 21 Two other land-surface parameters used in the 1958) or the National Resources Conservation Service model for calculating direct runoff are (1) a measure of (Alan Walters, Natural Resources Conservation the distance between the smallest drainage channels in Service, written commun., 1997) indicated that till and the basin, and (2) the slope between such channels and outwash soils had different characteristics; (2) the drainage divides separating them (Bauer and Horizontal hydraulic conductivities of soils generally Mastin, 1997). Values for these parameters were were set to as much as two orders of magnitude greater obtained from a previous study in western Washington than the vertical hydraulic conductivities; (3) Specify (Bauer and Mastin, 1997) with similar glacial initial water content of the soil. The amount of soil topography. water is expressed as a fraction of the available water- holding capacity (unsaturated soil) and as a fraction of Other Data specific yield (saturated soil). The start of the simulation for the six basins was October 1997. Based Additional variables used by the DPM to on examination of prior precipitation quantities, the simulate atmospheric and land-cover processes include initial soil moisture as a fraction of available water- sublimation rates for snowpack, snowmelt coefficient, holding capacity for all the basins was estimated to be monthly maximum possible solar radiation, and 30 percent. maximum interception storage capacity for land covers Measured runoff (RUNOFF, Appendix A, tables where throughfall data were not available. These A1 through A6, at back of report) for the study basins variables were assigned values from Bauer and Mastin was compared to simulated runoff for the island-wide (1997), or default values from the DPM. models (SYM-RO, Appendix B, tables B1 and B2, at back of report). By continued adjustment of horizontal Model Adjustment and vertical hydraulic conductivity values of soils and The DPM recharge analysis was done for each of subsoils in the DPM, monthly and annual SYM-RO the six study basins. For each study basin, various values were simulated to match as closely as possible DPM parameters were adjusted in order to minimize to measured runoff. In addition, soil-saturation deficit the value of DEFCIT and also to achieve the smallest values (DEFCIT, Appendix A, tables A1 through A6) difference between measured and simulated runoff were minimized by adjusting vertical hydraulic values (RUNOFF) and fluxes of water (see section conductivities and initial soil permeabilities (DEFCIT "Near-Surface Water-Balance Method"). Such a is the amount of streamflow not accounted for). balance was achieved primarily by adjusting values Differences between values of measured and simulated assigned to the vertical hydraulic conductivity of the runoff generated by DPM when measured runoff was subsoil and to the soil depths and water-holding not used for the study basins range from about 1 to 7 capacities. Three distinct subsoils composed of glacial inches. deposits were identified in the study area: clay, till, and outwash. Soils underlain by clay generally have lower Average Measured monthly vertical hydraulic conductivity and allow less recharge Gaging Basin runoff simulated than soils underlain by till and outwash deposits. station (inches) runoff Subsoil materials in the study basins and islands were (inches) determined using data from a soil survey of Island County (U.S. Department of Agriculture, 1958; and Southern Camano Island 12170305 7.15 6.90 Jones, 1999). None of the study basins contain bedrock Northern Camano Island 12170310 5.77 1.38 in the subsoil. Northern Whidbey Island 12170315 0.90 3.53 The model adjustments were: (1) Vertical Penn Cove 12170320 1.70 1.73 hydraulic conductivities of subsoils were adjusted to 2 Cultus Creek 12170400 4.32 5.32 inches per year for clay; 5 to 20 inches per year for till; South Whidbey State Park 12170440 8.94 3.15 and 20 to 200 inches per year for outwash. Different Reducing these differences further for all basins was values of hydraulic conductivities were assigned to till not possible to achieve because changing a parameter and outwash soils when information from the Soil to improve the DEFCIT for one basin increased Conservation Service (U.S. Department of Agriculture, DEFCIT in other basins.

22 Estimating Ground-Water Recharge from Precipitation on Whidbey and Camano Islands, Island County, Washington, for Water Years 1998 and 1999 After model adjustment, the average simulated Islands. Input data for the island-wide DPM annual deep percolation (recharge) values, in inches per simulations were compiled in a similar manner as for year, for the six study basins from October 1997 to the study-basin simulations. Land-use and soil data September 1999 were: coverages used in the DPM for each island are shown in tables 7 and 8, and in figures 7 and 8. Average Simulated recharge annual precipitation assigned to island-wide model Gaging Basin (inches per year) cells were interpolated from spatially gridded data station WY1998 WY1999 Average produced by the PRISM model using annual precipitation data averaged for 1961-90 (Oregon Southern Camano 12170305 5.45 7.27 6.36 Climate Service, 1999, fig. 3). Adjusted vertical Island hydraulic conductivities of the subsoil, soil depth, and Northern Camano 12170310 3.17 3.85 3.51 lateral permeability of the soil were from the study Island basins for the corresponding subsoil materials and soil Northern Whidbey 12170315 5.50 6.38 5.94 Island types. Penn Cove 12170320 2.21 3.68 2.94 Simulated average annual recharge, in inches per Cultus Creek 12170400 5.96 6.62 6.29 year, during water years 1998-99 was 5.71 for Whidbey South Whidbey State 12170440 2.14 2.54 2.34 Island and 5.98 for Camano Island (Appendix B, tables Park B1 and B2). The areal distribution of simulated average annual recharge for each island (fig. 9) reflects Average annual precipitation in the study basins variations in precipitation amounts (fig. 3) and the (PRECP, Appendix A, tables A1 through A6) for water distribution of surficial materials (fig. 4). Recharge years 1998-99 ranged from 15 to 26 percent above the generally is higher in areas underlain by coarse-grained long-term (1961-90) average annual precipitation deposits (outwash) than in areas underlain by fine- computed from gridded precipitation data using the grained deposits (till). DPM-simulated recharge in PRISM model (Oregon Climate Service, 1999). areas underlain by fine-grained deposits generally were Because precipitation is the primary source of recharge less than 10 inches per year. DPM-simulated recharge in the study basins, a 15- to 26-percent increase in in areas underlain by coarse-grained deposits precipitation would lead to a corresponding but not commonly ranged from 10 to 20 inches per year, and as necessarily equal increase in DPM simulated recharge. high as 25 inches per year in some areas (fig. 9). Other conditions, such as antecedent soil moisture in the study basins, may affect the amount of Table 7. Land-cover categories used in the Deep Percolation Model recharge that occurs in response to a precipitation (DPM) for Whidbey and Camano Islands, Island County, Washington event. Precipitation during 1997, the year prior to data [–, no data] collection, as recorded at Coupeville, Washington (fig. 1) by the National Oceanic and Atmospheric Whidbey Island Camano Island Administration (1997) indicates that this period was Area Area about 25 percent wetter than the long-term average (30- DPM land cover Area Area (square (square (percent) (percent) year) at the Coupeville station. Because less miles) miles) precipitation is needed to replenish soil moisture following a wet year, more water is available for Coniferous forest 103 61 29.2 75 recharge and thus actual recharge may be higher than Grass 24.5 15 5.4 14 recharge simulated by the DPM for the study period. Alfalfa 24.9 15 4.04 10 Open water 8.55 5 0.34 1 Island-Wide Recharge Estimates for Whidbey and Camano Orchard 4.53 3 – – Islands Using the Deep Percolation Model Bare ground 1.65 1 .12 <1 Shrub/brush .37 <1 – – Adjusted model input values and parameters from the six study basins were used in the DPM Total 167.5 39.1 simulations of the entire areas of Whidbey and Camano

Estimates of Ground-Water Recharge 23 Table 8. Soil groups composited for the Deep Percolation Model using Island County soil series for Whidbey and Camano Islands, Island County, Washington

[Area: Sum of cell areas used in DPM. Percentages do not always equal 100 percent because of rounding and may not agree exactly with similar percentages in other tables in this report. –, no data]

DPM soil Whidbey Island Camano Island group Soil series Area Area Area Area (see fig. 7) (square miles) (percent) (square miles) (percent)

1 Coastal beach – – 0.65 1.6 Ebeys 1.2 0.72 .02 .06 Hovde .51 .30 .09 .23 Hoypus 29.0 17.0 Indianola – – 6.3 16.0 Keystone 25.1 15.0 – – Pondilla .19 .11 – – San Juan 1.5 .92 – –

2 Rough broken land 2.6 1.6 1.2 3.1

3 Snakelum .79 .47 – –

4 Alderwood – – 20.0 50.0 Townsend 3.04 1.8 .16 .40 Whidbey 70.0 42.0 – –

5 Swantown 6.8 4.0 – –

6 Bow – – 4.6 11.0 Bozarth .28 .17 – –

7 Bellingham .99 .59 .97 2.46 Casey 8.5 5.0 – – Tidal marsh 1.0 0.62 .26 .66

8 Coupeville 2.2 1.3 .01 .03 Coveland 3.2 1.9 .04 .10 Lummi 1.8 1.1 .47 1.2 Norma 3.1 1.8 .40 1.0

9 Puget – – .33 .84

10 Carbondale .28 .16 – – Semiahmoo .93 .56 .06 .14 Tacoma .51 .31 .01 .02 Tanwax .70 .42 .12 .29 Fresh water marsh .11 .06 .01 .03 Greenwood .11 .06 – – Mulkilteo 1.3 .75 .06 .15 Rifle 1.0 .61 .10 .24

11 Everett – – 3.8 9.64

12 Rough stony land .36 .22 – – Made land .95 .57 .02 .05

Total 168.05 39.68

24 Estimating Ground-Water Recharge from Precipitation on Whidbey and Camano Islands, Island County, Washington, for Water Years 1998 and 1999 122°45' 122°22'30"

0 24 6 MILES

0 24 6 KILOMETERS 48° 22' 30" T 33 N

S kagit Bay

STRAIT OF JUAN DE FUCA

Penn Cove

CAMANO

S ISLAND WHIDBEY a r atoga Passage ISLAND Port T Susan 31 Admi N ralty Inlet

EXPLANATION SIMULATED AVERAGE ANNUAL RECHARGE, IN INCHES PER YEAR 0 - 4.00 4.01 - 8.00 T 48° 8.01 - 12.00 29 N 12.01 - 16.00 16.01 - 20.00

Inactive model cell; deep percolation not determined BOUNDARY OF DRAINAGEBASIN BOUNDARY OF STUDY AREA

Base modified from U.S. Geological Survey R.1 E. R.3 E. digital data, 1:2,000,000, 1972 Universal Transverse Mercator projection, Zone 10

Figure 9. Distribution of average annual recharge simulated by the Deep Percolation Model, Island County, Washington.

Estimates of Ground-Water Recharge 25 In order to assess the validity of the island-wide downward drainage below the root zone, as simulated simulations, average annual recharge estimates from with the DPM; (2) assumptions concerning equivalency study-basin simulations were compared to average of downward drainage from the root zone and recharge annual recharge from the island-wide simulations for to ground water; and (3) assumptions involved with the same study basin areas for the same period of time scaling up results from study basins to estimate annual (water years 1998-99). recharge for entire island areas. There are several sources of error associated with Average annual recharge water-balance components that were derived for the (inches) study basins, including the sources listed below. Gaging Basin Island-wide • Errors are associated with the collection of field station Study-basin simulations data. Precipitation can greatly vary from one simulations for the study basin location to another for any particular storm. Therefore, errors in the water balance can develop Southern Camano 12170305 6.4 5.1 when precipitation and precipitation throughfall at Island one or two measuring points are used to represent Northern Camano 12170310 3.5 4.4 the precipitation and precipitation throughfall for a Island drainage basin. Moreover, the forest throughfall Northern Whidbey 12170315 5.9 4.3 data are subject to additional error because of the Island wide variety of age, density, and species within the Penn Cove 12170320 2.9 3.1 forested areas. Data-collection sites selected may Cultus Creek 12170400 6.3 5.9 or may not be fully representative of the larger South Whidbey State 12170440 2.3 3.2 Park forested areas. • Malfunctions in data-collection instruments Differences between average annual recharge for require that streamflow and precipitation be study-basin and island-wide simulations ranged from estimated from regression analyses. 0.2 to 1.6 inches, and averaged 0.88 inch. The magnitude of these differences is small, but because of • The best streamflow data are considered accurate the small amount of recharge, the percentage of to only about 5 percent, and due to the small size differences range from about 7 to 39 percent. The of the streams in this study, probably only a 10- output summary tables of the island-wide DPM percent accuracy was achieved. simulations, which present monthly water-budget • A reliable means for computing direct runoff from components, are shown in Appendix B. total streamflow is not available, and subjective estimates of baseflow were used. This source of Sources of Uncertainty in DPM Recharge Estimates error would only be significant for the northern In the construction of numerical models, Whidbey Island (12170315) and Cultus Creek sensitivity or uncertainty analyses are often done to (12170400) study basins. The other study basins assess which input parameters have the most "control" did not have baseflow during the period of study. of model output. In the case of the DPM, because • Errors in assignments to DPM parameters used to recharge generally is unknown and there is no characterize soil and plant properties could have "calibration" of the model (with the exception of caused errors in the modeled simulations of the streamflow), such analyses were not done. Values for water balances and ultimately recharge. the soil parameters were the least known and most • Little published information exists concerning often were adjusted during the DPM simulations. transpiration in western Washington with which to Although the uncertainties in recharge estimates verify that transpiration estimates were accurate. using the DPM could not be quantified, their major Simulated transpiration in this study accounted for sources, nonetheless, warrant discussion. Sources of a substantial percentage (from 24 to 38 percent) of uncertainty fall into three main groups: (1) factors and precipitation on an average annual basis. However, conditions that affect the reliability of estimates of

26 Estimating Ground-Water Recharge from Precipitation on Whidbey and Camano Islands, Island County, Washington, for Water Years 1998 and 1999 during the dormant winter periods, transpiration Additional errors may result from extending the error relative to precipitation is small because recharge results of the 2-year water balance from the transpiration is small. Transpiration error also study basins to estimates of island-wide recharge. The probably is small during summer and autumn assumption was made that the parameters that control when all available soil moisture is transpired recharge and direct runoff are identical for similar during this time. Errors in transpiration values geologic, soil, land-cover, and precipitation conditions. during times when soil moisture is at field Without actual measurement of streamflow for all capacity during the growing season would result drainage basins, this assumption could lead to errors at in greater errors in calculated recharge. The locations where extrapolated parameter conditions do greatest potential for error in calculated recharge not reflect actual parameter heterogeneity. For during this study is during the months of March example, an area mapped as coarse-grained outwash through May. may, in part, be underlain by fine-grained till. This • Errors associated with PRISM precipitation data. would result in local recharge estimate error comparable to the range in recharge depicted in Equating recharge to the downward flow below figure 9. the root zone also could lead to errors. In most environments, water that percolates below a few feet from the soil surface is destined to recharge a saturated Chloride Mass-Balance Method system (extremely arid environments can be an exception, where bare soil evaporation may be a large The chloride mass-balance method was used as a component of ground-water discharge). A second, independent means of estimating recharge in hydrogeologic system can contain multiple unsaturated the study area. This method was used to estimate zones that are separated by saturated zones. The combined recharge to both Whidbey and Camano arrangement and vertical and horizontal extents of Islands. The chloride mass-balance method for saturated and unsaturated zones in areas underlain by estimating recharge is based on the principle that a glacial deposits may be complex. As a result, not all known fraction of chloride in precipitation and dry- water that percolates downward below a root zone atmospheric deposition is transported to the water table necessarily becomes recharge to the saturated zone that by the downward flow of water. As water percolates has been identified as an aquifer in the hydrogeologic downward, some evaporates directly or is taken up and framework. For example, water percolating through transpired by plants. Where this occurs, the predominantly unsaturated materials below a root zone, concentration of chloride in soil water increases with upon meeting a layer of fine-grained sediments with depth because little or no chloride is lost by these low hydraulic conductivity, could recharge a thin, processes. At greater depths, where no saturated zone not tapped by wells, flow laterally, and evapotranspiration occurs, the chloride concentration discharge to a stream or spring. The water in this should be uniform if climate, soil, and other conditions example might not reach the saturated ground-water- near the surface have been steady for a sufficiently long flow system that is used as a source of water to wells. time.

Estimates of Ground-Water Recharge 27 The chloride mass-balance method is based on assumptions are that (5) minerals in the soil are not a the assumption that precipitation and dry-atmospheric source of chloride, and the only sources are deposition are the only sources of chloride in ground precipitation and dry-atmospheric deposition, (6) water and in surface-water runoff. Human sources such measured chloride concentrations are at depths great as septic systems and animal sources such as cow enough that seasonal variations in concentration are manure contribute minimal amounts of chloride to the small, and (7) the concentration of chloride in surface- water in the study area, and natural sources such as water runoff is the same as that in precipitation. The evaporite rocks or connate seawater are not present in method is still valid if chloride is taken up by growing the hydrogeologic units above sea level. Another vegetation as long as it is also released by decaying possible source of chloride is residual chloride from vegetation at the same rate. early post-ice-age seawater that may have intruded the glacial materials while the island was below sea level Data Collection from the time after the glaciers retreated and before the The chloride mass-balance method involves island isostatically rebounded to above sea level sampling chloride from the atmosphere (precipitation (Culhane, 1993). A mass balance of chloride in and dry deposition), the water-table aquifer, and/or the precipitation, surface runoff, and ground water is unsaturated-zone soil moisture. Chloride expressed in the following equation (Prych, 1995; concentrations were determined from samples of Maurer and others, 1996): precipitation and dry-atmospheric deposition from May 20, 1998 through April 9, 1999 and from ground- PC× p = ()GWR× Cg + ()SWR× Cp ,(2)water samples collected in the autumn of 2000. Two atmospheric-chloride deposition-collection sites were where established — one on northern Whidbey Island and the P is annual precipitation, in inches; other on southern Camano Island (fig. 1). A wet and Cp is concentration of chloride in precipitation, in dry atmospheric-deposition sampler was installed at the milligrams per liter; sites. The sampler consists of two buckets mounted on GWR is annual ground-water recharge, in inches; an electromechanical device that senses precipitation Cg is concentration of chloride in ground water, in and automatically places a cover on one or the other of milligrams per liter; and the buckets. During periods of precipitation, the "dry" SWR is annual surface-water runoff, in inches. bucket is covered while the "wet" bucket collects precipitation. When it is not raining, the "wet" bucket is Rearranging the terms in equation 2 and solving covered to prevent any influx from the dry atmosphere for GWR gives: (including insects, bird droppings, and wind-blown ground debris) and to minimize evaporation. At the ()PC× – ()SWR× C GWR = ------p p- (3) same time, the dry bucket is open to collect Cg microscopic crystals of chloride salts that fall from the Implicit in the derivation and uses of equation 3 atmosphere. is the assumption of "plug flow," or piston flow, which The sampling buckets were collected and assumes that (1) the direction of water flow and replaced with clean buckets on a monthly basis. All chloride transport is vertical and downward, (2) areal bucket samples were weighed, and filtered aliquots distributions of the rate of percolation of water and of were sent to the USGS National Water-Quality chloride on the local scale (a few tenths of a meter) are Laboratory (NWQL) for low-level chloride uniform (no preferred pathways), (3) all chloride is determinations. Aliquots from the dry buckets were dissolved in soil water, and the distribution of the taken by first adding a known quantity of distilled dissolved chloride in the soil water is relatively water to the bucket, which was thoroughly swirled and uniform within a pore (no solid chloride phase, then sampled. Chloride concentrations in ground-water sorption by soil, or anion exclusion), and (4) advection samples from wells in the study area (fig. 1) also were is the dominant mode of chloride transport, and determined at the NWQL. diffusion is relatively unimportant. Additional

28 Estimating Ground-Water Recharge from Precipitation on Whidbey and Camano Islands, Island County, Washington, for Water Years 1998 and 1999 Recharge Estimates and Sources of Uncertainty Using In order to obtain a long-term average recharge Chloride Mass-Balance Method value from equation 4, the terms in this equation should Implicit in the derivation of equation 2 is the ideally also be long-term averages. Because of mixing assumption that all atmospheric chloride in soil water and generally multi-year residence times of water in is deposited by precipitation (wet deposition). most aquifers, Cg probably represents a long-term However, about 18 percent of the total chloride average. However, SWR and P are two-year averages deposition in the study area occurs as dry deposition and FWD is a one-year estimate. (table 9). Orr and others (2002) determined that about Owing to mechanical difficulties with the wet- 37 percent of the total chloride deposition in the San and-dry atmospheric-deposition samplers, a full year's Juan Islands of Washington occurred as dry deposition chloride deposition data were not obtained at either of during water years 1997-98. In that study, equation 3 the two sites. Continuous data were collected from July was modified to: 21, 1998 through April 9, 1999 at site 12170305 and from May 20, 1998 through December 8, 1998 at site 12170315. Consequently, the two data sites were GWR = 0.0394FWD()1 – SWR/P /Cg (4) combined to produce a single, longer period data set (May 20, 1998 through April 9, 1999). For those where periods when data were available from both collectors, FWD is the total of the wet and dry the total chloride flux values were computed for each chloride deposition expressed in site and averaged to provide single values (see table 9). mg/m2; Cg is in mg/L; and GWR, SWR, P are in inches.

Table 9. Summary of chloride in precipitation and dry-atmospheric deposition measured at two locations on Whidbey Island, Island County, Washington, May 1998 through April 1999

[Location: See figure 1 for locations 315 and 305; “avg” means that values are averages from locations 315 and 305; “est” means no data for this period and values are estimated from data for other periods. Chloride concentrations: Wet+dry buckets: Concentration resulting if chloride from dry bucket were added to wet bucket]

Measurement period Chloride concentrations Atmospheric chloride fluxes Year-month-day (in milligrams per liter) (milligrams per square meter) Location Wet Wet+dry In precipitation As dry Total of From To bucket buckets (wet) deposition (dry) wet+dry

05-20-98 06-19-98 315 0.28 1.5 3.6 15.0 19.0 06-19-98 07-21-98 315 .52 (1) 26.0 211.0 37.0 07-21-98 08-28-98 avg .44 12.0 3.4 35.6 39.00 08-28-98 10-06-98 avg .38 .60 9.9 5.7 16.0 10-06-98 11-03-98 avg .86 1.1 44.0 10.0 54.0 11-03-98 12-08-98 avg 1.30 1.4 170.0 17.0 180.0 12-08-98 01-20-99 est (4) (4) (4) (4) 2280.0 01-20-99 02-26-99 305 1.40 1.6 250.0 39.0 280.0 02-26-99 04-09-99 305 3.20 4.0 200.0 51.0 250.0 04-09-99 05-20-99 est (4) (4) (4) (4) 2130.0

1Sample lost or destroyed. 2Value estimated from preceding and following data periods. 3Average values adjusted to account for different time periods for the two stations. 4Data not collected during this period.

Estimates of Ground-Water Recharge 29 For the period when both collectors were operating, the well could develop. The only potential migration of total chloride fluxes were similar, 85.73 mg/m2 at site chloride from seawater would be by diffusion, which 12170315 and 70.06 mg/m2 at site 12170305. In order would only occur over distances that are small to extend the data set to represent a full year of compared with distances from seawater to such wells. deposition, it was first assumed that the seasonal Chloride concentrations for the 12 wells sampled pattern of chloride deposition is similar from year to ranged from 6.4 to 44.4 mg/L and averaged 21.8 mg/L year and therefore, chloride flux values could be (table 10). interpolated between months regardless of the year Surface-water runoff, SWR (also referred to as associated with the month. Accordingly, average daily "direct runoff") and precipitation, P, in equation 4 were deposition rates were calculated for the first and last estimated from the same six gaging stations in the periods in the measured data set and an average of their study basins that were used to estimate recharge using rates was applied to the part of the year (April 10 to the DPM (tables 1 and 5). When averaged over the six May 20) when data were missing. The annual chloride study basins for the 2-year period, SWR and P are 5.07 deposition estimated in this manner was 1,268 mg/m2. and 28.04 inches per year. Using the annual average Ground-water samples used for determining Cg values for the variables discussed above in equation 4, (eq. 4) were collected from wells where the only source the combined average annual recharge for Whidbey of chloride in the aquifer was from the atmosphere and Camano Islands is 2.00 inches for water years (fig. 1 and table 10). Samples from any wells that may 1998-99, about 17 percent of the average annual be intruded by seawater could not be used. One recharge estimated for Whidbey and Camano Islands requirement that assures that there would be no using the DPM. Orr and others (2002) reported an seawater intrusion is that the bottoms of the wells be annual recharge estimate for Lopez Island using the above sea level. For such wells, the water levels cannot chloride mass-balance method that was about 23 be drawn down by pumping to below sea level, and percent of the annual recharge estimated for Lopez therefore, no potential gradient from seawater to the Island using the DPM.

Table 10. Summary of selected physical characteristics and chloride concentrations for wells used in the chloride-mass balance, Whidbey Island, Island County, Washington, water years 1998-99

Chloride, Altitude of Altitude of Well depth dissolved Well No. Island land surface bottom of (feet below (milligrams (feet) well (feet) land surface) per liter)

28N/03E-10L02 Whidbey 255 206 49 16.4 29N/02E-09A02 Whidbey 165 76 89 14.9 29N/03E-35E01 Whidbey 310 274 36 9.8 29N/04E-31D02 Whidbey 180 156 24 6.4 29N/03E-02G02 Whidbey 150 73 77 8.93

30N/02E-08P01 Whidbey 265 68 197 16.6 30N/03E-23C04 Camano 150 82 68 8.41 31N/01E-11G01 Whidbey 188 63 125 44.4 31N/02E-32E01 Whidbey 265 209 56 33.6

31N/03E-30Q02 Camano 84 10 74 15.9 32N/03E-21D01 Camano 135 8 127 35.9 32N/01E-03B03 Camano 130 36 94 36.0

30 Estimating Ground-Water Recharge from Precipitation on Whidbey and Camano Islands, Island County, Washington, for Water Years 1998 and 1999 Attempts were not made to estimate the SUMMARY distribution of recharge from the data used for this method. For any particular sampling point within the The principal source of drinking water on aquifer, ground water generally has a predominantly Whidbey and Camano Islands, located off the horizontal flow component. Therefore, any ground- northwestern coast of Washington, is ground water water sample consists of an unknown mixture of water, derived from unconsolidated glacial and interglacial consisting of water percolating vertically downward deposit aquifers. Some uncertainty exists regarding the from recharge at the surface and from other upgradient quantity of recharge from deep percolation of areas. Recharge computed from chloride precipitation reaching the aquifers used for water concentrations in single samples of ground water supply. In 1998, the U.S. Geological Survey, in would therefore represent upgradient composite cooperation with the Island County Health Department recharge. began a study to estimate the quantity of recharge from Equation 4 and the data collected can be used to precipitation to unconsolidated-deposit aquifers on estimate certain limiting values of recharge. For Whidbey and Camano Islands. Two methods were used example, areas with highly permeable subsoils would to estimate recharge from precipitation to produce no direct runoff and therefore would have the unconsolidated deposits on the islands — a daily near- largest amount of recharge and the lowest chloride surface water-balance method (DPM), and a chloride concentrations. Selecting the lowest chloride mass-balance method. concentration of 6.4 mg/L in ground water from The DPM uses a daily water and energy budget table 10, and setting SWR = 0 in equation 4, and approach to simulate recharge. In this method, the maintaining the annual value of atmospheric chloride model simulated daily moisture fluxes of precipitation, deposition, yields an annual recharge estimate of 7.81 evapotranspiration, direct runoff, and deep percolation inches. Selecting the highest chloride concentration of for October 1, 1997 through September 30, 1999 44.4 mg/L (table 10) and using direct runoff and (water years 1998-99) for six small drainage basins — precipitation values from the study basin with the four on Whidbey Island and two on Camano Island. highest direct runoff to precipitation ratio results in an The DPM requires precipitation, precipitation estimated minimum annual recharge of 0.78 inch. throughfall, streamflow, shortwave solar radiation, air Sources of chloride in ground water other than temperature, surficial material properties, land-cover, from the atmosphere would cause recharge estimated and land-surface altitude data. Surficial material (soil by the chloride mass-balance method to be less than the and subsoil) parameters were estimated for the actual recharge. This is evident from equation 3, in different geologic and soil conditions in each of the six which the computed recharge is inversely proportional small basins during DPM adjustment. Model to the chloride concentration in ground water, if the parameters were adjusted until the difference between other variables remain unchanged. Therefore, the measured and simulated daily flows and fluxes of water recharge values of from 0.78 to 7.81 inches per year were minimized. Adjusted parameters from the DPM computed by the chloride-mass balance method may for each small basin were then used in island-wide represent lower limits, which is consistent with the DPM simulations. A spatial distribution of annual generally higher simulated recharge using the DPM for recharge was simulated for each island, with island the study basins (4.36 to 8.44 inches per year). averages of 5.71 inches per year for Whidbey Island and 5.98 inches per year for Camano Island. The

Summary 31 spatial distribution of simulated annual recharge for Bidlake, W.R., and Payne, K.L., 2001, Estimating recharge each island reflects variations in precipitation amounts to ground water from precipitation at Naval Submarine and the distribution of surficial materials. DPM results Base Bangor and vicinity, Kitsap County, Washington: indicate recharge generally is higher in areas underlain U.S. Geological Survey Water-Resources Investigations by coarse-grained deposits (outwash) than in areas Report 01-4110, 33 p. underlain by fine-grained deposits (till). DPM- Cline, D.R., Jones, M.A., Dion, N.P., Whiteman, K.J., and Sapik, D.B., 1982, Preliminary survey of ground-water simulated recharge in areas underlain by fine-grained resources for Island County, Washington: U.S. deposits generally were less than 10 inches per year. Geological Survey Open-File Report 82-561, 46 p. DPM-simulated recharge in areas underlain by coarse- Culhane, Tom, 1993, High chloride concentrations in ground grained deposits commonly ranged from 10 to 20 water withdrawn from above sea level aquifers, inches per year, and as high as 25 inches per year in Whidbey Island, Washington: Washington State some areas. Department of Ecology Open-File Technical Report 93- A chloride mass-balance method was used to 07, 35 p. compute combined recharge to unconsolidated deposits Daly, Christopher, Neilson, R.P., and Phillips, D.L., 1994, A on Whidbey and Camano Islands. This method is based statistical-topographic model for mapping on the principle that a known fraction of chloride in climatological investigation over mountainous terrain: precipitation and dry-atmospheric deposition is Journal of Applied Meteorology, v. 33, p. 140-158. transported to the water table by the downward flow of Easterbrook, D.J., 1968, Pleistocene stratigraphy of Island County: State of Washington Department of Natural water. The chloride mass-balance method requires Resources, Water Supply Bulletin No. 25, Part I, 35 p. measurements of atmospheric chloride deposition, Eriksson, Erik, and Khunakasem, Vachi, 1969, Chloride precipitation, streamflow, and chloride concentrations concentration in groundwater, recharge rate and rate of in ground water. The average combined recharge for deposition in the Israel coastal plain: Journal of Whidbey and Camano Islands estimated by this Hydrology, v. 7, p. 178-197. method was 2.00 inches per year. The range of chloride James, L.G., Erpenbeck, J.M., Bassett, D.L., and Middleton, concentrations in ground-water samples from selected J.E., 1988, Irrigation requirements for Washington— wells indicates that the average recharge to Estimates and methodology: Washington State unconsolidated deposits is between 0.78 and 7.81 University, Cooperative Extension, EB 1513, 37 p. inches per year. Sources of chloride in ground water Jones, M.A., 1999, Geologic framework for the Puget Sound other than from the atmosphere would cause recharge aquifer system, Washington and British Columbia: U.S. estimated by the chloride mass-balance method to be Geological Survey Professional Paper 1424-C, 31 p., 18 pl. less than the actual recharge, therefore, these estimates Maurer, D.K., Berger, D.L., and Prudic, D.E., 1996, may represent lower limits. Subsurface flow to Eagle Valley from Vicee, Ash, and Kings Canyons, Carson City, Nevada, estimated from Darcy's Law and the chloride-balance method: U.S. REFERENCES CITED Geological Survey Water-Resources Investigations Report 96-4088, 74 p. Anderson, H.W., 1968, Ground-water resources of Island National Oceanic and Atmospheric Administration, 1997, County: State of Washington Department of Natural Climatological Data Annual Summary, Washington, Resources Water Supply Bulletin No. 25, Part II, 318 p. 1997, v. 101, No. 13, unnumbered. Bauer, H.H., and Mastin, M.C., 1997, Recharge from Oregon Climate Service, 1999, 1961-90 annual average precipitation in three rural glacial-till mantled precipitation contours: Washington, accessed July catchments in the Puget Sound Lowland, Washington: 1999, URL http://www.ocs.orst.edu/pub/maps/ U.S. Geological Survey Water-Resources Investigations Precipitation/Total/States/WA/wa.gif. Report 96-4219, 119 p. Orr, Laura A., Bauer, Henry H., and Wayenberg, J.A., 2002, Bauer, H.H., and Vaccaro, J.J., 1987, Documentation of a Estimates of ground-water recharge from precipitation deep percolation model for estimating ground-water to glacial-deposit and bedrock aquifers on Lopez, San recharge: U.S. Geological Survey Open-File Report 86- Juan, Orcas, and Shaw Islands, San Juan County, 536, 180 p. Washington: U.S. Geological Survey Water-Resources Investigations Report 02-4114, 114 p.

32 Estimating Ground-Water Recharge from Precipitation on Whidbey and Camano Islands, Island County, Washington, for Water Years 1998 and 1999 Pessel, F. Jr., Dethier, D.P., Booth, D.B., and Minard, J.P., Vogelmann, J.E., Sohl, T.L., Champbell, P.V., and Shaw, 1989, Surficial geologic map of Port Townsend 30- by D.M., 1998, Regional land cover characterization using 60-minute quadrangle, Puget Sound region, Landsat thematic mapper data and ancillary data Washington: U.S. Geological Survey Miscellaneous sources: Environmental Monitoring and Assessment, Investigations Series Map I-1198-F, 1 sheet, scale v. 51, p. 415-428. 1:100,000, with 13 p. text. Western Region Climate Center, 2001, Coupeville IS, Prych, E.A., 1995, Using chloride and chlorine-36 as soil- Washington (451783), Period of Record Monthly water tracers to estimate deep percolation at selected Climate Summary, Accessed September 6, 2001, URL locations on the U.S. Department of Energy Hanford http://www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?wacoup. site, Washington: U.S. Geological Survey Open-File Whetten, J.T., Carroll, P.I., Gower, H.D., Brown, E.H., and Report 94-514,125 p. Pessel, F., Jr., 1988, Bedrock geologic map of Port Sapik, D.B., Bortleson, G.C., Drost, B.W., Jones, M.A., and Townsend 30- by 60-minute quadrangle, Puget Sound Prych, E.A., 1988, Ground-water resources and region, Washington: U.S. Geological Survey simulation of flow in aquifers containing freshwater Miscellaneous Investigations Series Map I-1198-G, and seawater, Island County, Washington: U.S. 1 sheet, scale 1:100,000. Geological Survey Water-Resources Investigations Yount, J.C., and Gower, H.D., 1991, Bedrock geologic map Report 87-4182, 67 p. of the Seattle 30- by 60-minute quadrangle, Thomas, B.E., Goodman, L.A., and Olsen, T.D., 1999, Washington: U.S. Geological Survey Open-File Report Hydrogeologic assessment of the Sequim-Dungeness 91-147, 37 p., 4 pl. area, Clallam County, Washington: U.S. Geological Yount, J.C., Minard, J.P., and Dembroff, G.R., 1993, Survey Water-Resources Investigations Report 99- Geologic map of surficial deposits in the Seattle 30- by 4048, 165 p. 60-minute quadrangle, Washington: U.S. Geological University of Washington, 2000, Washington State Survey Open-File Report 93-233, 2 sheets, scale Geospatial Data Archive, accessed September 2000, 1:100,000. URL http://wagda.lib.washington.edu/data. U.S. Department of Agriculture, 1958, Soil Survey, Island County, Washington: Soil Conservation Service Series 1949, No. 6, 58 p.

References Cited 33 ; .00 .00 .00 .00 .00 .00 .00 .04 .02 .00 .02 .00 .00 .00 .00 .00 .00 -.01 -.16 -.05 -.04 -.01 0.00 0.07 , actual -0.01 -0.26 DEFCIT RUNOFF APLTR Continued 49.7 44.6 39.9 40.1 43.9 44.5 46.5 52.4 56.0 61.5 59.2 55.4 49.5 48.3 45.3 38.4 40.7 41.2 42.2 44.0 49.1 55.5 57.8 59.7 53.9 48.0 AV T M P All values rounded to two to two rounded All values 2170305 2170305— ted throughfall tedwhere throughfall land use is not .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 0.00 0.00 0.00 0.00 CHGSNW ging Station 1 lt + starting soil moisture ofin excess .45 .33 .39 .66 .74 .63 .58 .38 .22 .05 .40 .31 .34 .53 .61 .81 .21 1.05 1.07 6.56 0.71 1.10 0.93 1.33 1.42 8.69 EVINT ch is in degrees Fahrenheit. ch is in degrees ive: rain + snowmelt – (available water-holding capacity water-holding – (available rain + snowmelt ive: Camano Island, Ga , foliage-type-dependent potential transpiration; -.02 -.16 -.23 -.39 -.11 -.03 -.72 3.19 1.34 0.23 1.51 2.69 3.25 2.24 1.17 0.54 -1.91 -1.81 -2.17 -1.02 -1.42 -1.63 -1.08 -2.12 -1.83 -1.31 CHGSM PPLTR precipitation throughfall, and DPM-simula precipitation throughfall, .07 .00 .00 .02 .40 .39 .00 .00 .00 .00 .26 0.08 1.66 1.92 2.42 2.26 1.16 0.29 1.26 1.25 1.45 2.68 1.88 1.31 APLTR 10.38 10.39 , if the following is negative: rain + snowme is negative: , if the following rect runoff; if the following is posit is if the following runoff; rect GET SUMMARIES FOR THE SIX STUDY BASINS GET SUMMARIES FOR THE SIX rn Camano Island study basin, Water Year 1998 Year Water 1999 Year Water .07 .00 .00 .02 .40 .00 .00 .00 .00 .26 es in inches of water except AVTMP, whi es in inches AVTMP, of except water than sum of evaporation and transpiration components, as discussed in report); report); in as discussed components, transpiration and of evaporation than sum 0.08 1.66 1.97 2.55 3.07 3.26 2.25 0.31 1.27 1.27 1.49 2.84 2.14 2.01 PPLTR 15.35 11.59 DEFCIT low the rootzone (recharge); low .38 .89 .91 .73 .07 .00 .00 .00 .00 .58 .71 .72 .59 .17 .01 .00 0.06 1.36 1.05 5.45 0.01 1.09 1.19 1.17 1.03 7.27 RECHRG , interception loss computed from input , average temperature; , average .15 .77 .82 .16 .04 .00 .00 .00 .15 .32 .16 .13 .11 .00 .00 .00 EVINT 0.11 3.07 1.15 1.84 8.12 0.00 1.36 3.29 1.37 6.89 RUNOFF AV T M P ; soil water that percolates; soil water be and transpiration components – measured di easured direct runoff – recharge. All valu – recharge. easured direct runoff , potential evapotranspiration be less (may potential evapotranspiration , .56 .33 .39 .69 .40 .31 .34 .53 1.2 1.6 3.0 3.3 4.1 4.6 4.7 3.1 1.13 1.47 2.66 3.06 3.46 4.49 3.74 2.97 28 24.56 POTET RECHRG POTET , change in soil moisture; , change in snowpack; change in snowpack; , .48 .36 .05 .87 .21 4.6 2.4 2.0 6.3 2.8 4.2 2.0 2.5 1.2 3.74 4.46 4.03 4.07 4.87 3.68 1.43 2.76 2.45 1.34 e of rounding totals may not exactly equal the sum of the shown monthly values] monthly equal the sum shown of totals may not exactly e of rounding PRECP 29 33.88 CHGSM CHGSNW Year Year 1997 1997 1997 1998 1998 1998 1998 1998 1998 1998 1998 1998 1998 1998 1998 1999 1999 1999 1999 1999 1999 1999 1999 1999 . southe the for summaries water-budget computed annual and Monthly . Monthlyand annual computedwater-budget summaries for the southernCamanoIsland studybasin, CamanoIsland, GagingStation 1 DATE , measured precipitation; Totals Month Month Totals PRECP October November December January February March April May June July August September October November December January February March April May June July August September available water-holding capacity - evaporation capacity - evaporation water-holding available Becaus figures. significant evergreen forest; evergreen yield – starting soil moisture)+ specific – m plant transpiration; APPENDIX A. MONTHLY COMPUTER WATER-BUD A1 Table [ measured or estimated direct runoff; Table A1

34 Estimating Ground-Water Recharge from Precipitation on Whidbey and Camano Islands, Island County, Washington, Water Years 1998 and 1999 .01 .00 .01 .00 .00 .00 .00 -.01 -.06 -.02 -.02 0.00 -0.09 Continued 49.0 44.9 39.1 40.4 42.5 43.3 45.2 50.8 55.8 59.6 59.4 54.7 48.8 2170305— .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 0.00 .43 .32 .37 .60 .83 .98 .50 .52 .13 0.88 1.09 1.00 7.62 Camano Island, Gaging Station 1 -.06 -.10 -.47 -.85 2.94 2.30 1.24 1.34 -1.77 -1.44 -2.14 -1.43 -0.44 .04 .00 .00 .01 .33 .85 0.18 1.46 1.59 1.94 2.47 1.52 10.38 .04 .00 .00 .01 .33 rn Camano Island study basin, rn Camano Island 0.19 1.46 1.62 2.02 2.95 2.70 2.13 13.47 Average monthly values monthly Average .48 .99 .72 .39 .29 .08 .01 0.04 1.28 1.04 1.04 6.36 000 .15 .55 .49 .15 .07 .00 .00 .00 0.06 2.21 2.22 1.61 7.51 .48 .32 .37 .61 1.14 1.54 2.84 3.20 3.77 4.54 4.21 3.05 26.07 .91 .61 .13 4.16 3.43 3.04 5.20 3.82 3.93 1.69 2.63 1.82 31.35 . southe the for summaries water-budget computed annual and Monthly DATE PRECP POTET RUNOFF RECHRG PPLTR APLTR CHGSM EVINT CHGSNW AVTMP DEFCIT Month October November December January February March April May June July August September Totals Table A1

Appendix B 35 , , , .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 -.01 -.15 -.52 -.09 -.18 -.20 -.01 -.38 -.35 -.21 -.27 -.26 0.00 -0.02 -1.18 -1.48 DEFCIT AV T M P EVINT CHGINT ; soil water that ; soil water Continued AV T M P 48.0 42.5 38.2 38.8 42.3 42.5 43.9 50.5 53.4 57.8 55.5 51.6 47.1 45.7 44.0 37.2 39.3 39.6 40.1 41.1 46.7 54.0 55.6 57.2 50.7 46.0 ation and transpirationation and RECHRG rounding totals may not 12170310 170310— , change in snowpack; change in snowpack; , , change in soil moisture; .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 0.00 0.00 0.00 0.00 CHGSNW CHGSNW CHGSM forest; .52 .64 .63 .89 .39 .45 .32 .01 .20 .64 .92 .88 .39 .43 .47 .33 .29 .13 icant figures. Because of icant figures. components, as discussed in report); in report); as discussed components, 0.91 1.07 1.01 7.04 0.70 1.19 1.09 7.46 ic yield - starting soil moisture) – measured direct EVINT e water-holding capacity– evapor e water-holding ; measured or estimated direct runoff; ; measured or estimated direct runoff; .23 .07 .04 .05 .67 .22 -.21 -.03 -.07 -.61 -.48 2.58 1.21 1.08 0.80 2.51 1.72 0.39 -1.14 -1.59 -1.33 -1.54 -0.55 -1.77 -1.38 -1.19 CHGSM , actual plant transpiration; tion and transpirationtion and RUNOFF .20 .08 .04 .22 .58 .13 .05 .04 .15 .46 0.36 1.49 1.76 2.11 2.28 1.51 0.44 0.50 1.35 1.53 1.76 2.38 1.90 1.33 APLTR APLTR 11.09 11.58 All values rounded to two signif rounded to two values All moisture in excess of availabl of moisture in excess .20 .08 .04 .22 .58 .13 .05 .04 .15 .46 roughfall where land use is not evergreen is not evergreen land use where roughfall 0.36 1.49 1.77 2.14 2.40 2.70 1.73 0.54 1.35 1.53 1.77 2.41 1.98 1.64 Water Year 1998 Year Water 1999 Year Water than sum of evapora PPLTR 13.73 12.03 (available water-holding capacityspecif + water-holding (available .02 .10 .67 .75 .78 .09 .11 .30 .31 .03 .00 .32 .36 .64 .71 .65 .09 .19 .23 .25 .10 .02 0.00 3.17 0.30 3.85 RECHRG which is in degrees Fahrenheit. Fahrenheit. degrees is in which .04 .45 .71 .42 .02 .00 .01 .00 .00 .04 .51 .40 .55 .04 .02 .00 .00 0.03 2.19 1.28 5.16 0.00 1.89 1.92 1.00 6.39 RUNOFF with land cover for which data arethroughfall with land used); cover , foliage-type-dependent potential transpiration; transpiration; potential , foliage-type-dependent pitation throughfall, pitationand DPM-simulated throughfall, th PPLTR .47 .32 .37 .56 .38 .33 .33 .50 , potential evapotranspiration (may be less , potential evapotranspiration 0.93 1.29 2.40 2.66 3.24 3.50 3.70 2.48 0.97 1.19 2.12 2.45 2.80 3.58 2.92 2.35 POTET the following is positive: rain + snowmelt – rain + snowmelt is positive: the following 21.91 19.91 POTET , if the following is negative: rain + snowmelt + starting soil rain + snowmelt is negative: , if the following 3.87 1.98 2.19 3.71 2.30 3.50 1.54 2.34 1.28 1.59 0.01 0.44 2.31 3.65 3.83 3.82 3.28 2.91 1.35 2.67 2.02 1.20 0.91 0.29 PRECP 24.75 28.24 the shown monthly values] monthly the shown DEFCIT Year Year 1997 1997 1997 1998 1998 1998 1998 1998 1998 1998 1998 1998 1998 1998 1998 1999 1999 1999 1999 1999 1999 1999 1999 1999 . Station Gaging Island, Camano basin, study Island Camano northern the for summaries water-budget computed annual and Monthly . 12 Station Gaging Island, Whidbey subbasin, Island Camano northern the for summaries water-budget computed annual and Monthly , measured precipitation; DATE Month Month Totals Totals PRECP October November December January February March April May June July August September October November December January February March April May June July August September interception loss computed frominterception loss input preci average temperature; average in inches AVTMP, of except water All values – recharge. runoff components – measured direct runoff; if if runoff; direct – measured components equal the sum ofexactly change in moisture stored on foliage (zero for cells percolates below the root zone (recharge); (recharge); zone the root below percolates Table A2 [ Table A2

36 Estimating Ground-Water Recharge from Precipitation on Whidbey and Camano Islands, Island County, Washington, Water Years 1998 and 1999 .00 .00 .00 .00 -.08 -.45 -.22 -.20 -.24 -.13 -0.01 -1.33 000 Continued 46.9 43.2 37.7 39.0 40.9 41.3 42.5 48.6 53.7 56.7 56.3 51.1 46.5 170310— .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 0.00 0.00 .58 .92 .76 .64 .41 .46 .33 .15 .17 0.80 1.00 1.05 7.25 .45 .02 .14 -.01 -.88 -.70 1.69 1.86 1.40 -1.04 -1.55 -1.46 -0.08 .16 .07 .04 .19 .52 .89 0.43 1.42 1.64 1.94 2.33 1.71 11.33 .16 .07 .04 .19 .52 0.45 1.42 1.65 1.96 2.41 2.34 1.68 12.88 Average monthly values monthly Average .17 .23 .66 .73 .71 .09 .15 .27 .28 .07 .01 0.15 3.51 .04 .48 .41 .28 .02 .02 .00 .00 0.02 2.04 1.32 1.14 5.77 .42 .32 .35 .53 0.95 1.24 2.26 2.56 3.02 3.54 3.31 2.42 20.91 .46 .36 3.09 2.81 3.01 3.76 2.79 3.20 1.44 2.50 1.65 1.39 26.49 . Monthly and annual computed water-budget summaries for the northern Camano Island subbasin, Whidbey Island, Gaging Station 12 DATE PRECP POTET RUNOFF RECHRG PPLTR APLTR CHGSM EVINT CHGSNW AVTMP DEFCIT Month October November December January February March April May June July August September To tals Table A2

Appendix A 37 , change .00 .00 .10 .00 .23 .00 .00 .00 .47 .93 .46 .00 .00 .00 .00 .00 .00 -.02 -.03 -.01 -.01 -.06 0.22 1.75 DEFCIT -0.03 -0.05 , interception loss CHGINT , average temperature; , average EVINT ; soil water that percolates ; soil water ual the sum of the shown of the shown ual thesum AV T M P 47.5 41.9 37.7 38.4 41.8 41.9 43.2 49.9 52.6 56.8 54.4 50.5 46.4 45.0 43.6 36.8 38.9 39.1 39.5 40.2 46.0 53.5 54.9 56.5 49.7 45.3 noff – recharge. All values in All values – recharge. noff AV T M P RECHRG Continued soil moisture; .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 0.00 0.00 0.00 0.00 CHGSNW ation and transpiration components – measuredtranspirationcomponents ation and , change in , change in snowpack; snowpack; , change in g totals may not exactly g totals may not eq exactly .58 .69 .52 .67 .44 .19 .44 .21 .21 .85 .99 .86 .53 .58 .57 .39 .32 .11 1.17 1.10 1.20 7.43 0.72 1.35 1.26 8.51 EVINT CHGSM il moisture) ° measured direct ru CHGSNW .59 .66 .64 .03 -.11 -.62 -.62 -.09 -.21 -.08 -.82 2.71 1.57 0.88 3.20 1.76 1.30 0.14 -2.22 -2.18 -1.28 -0.96 -1.32 -1.13 -2.02 -1.43 CHGSM ; measured or estimated direct runoff; ; measured or estimated direct runoff; e water-holding capacity – evapor – capacity e water-holding .26 .13 .09 .29 .75 .92 .30 .17 .06 .06 .15 .59 0.47 2.00 2.19 2.66 2.16 0.61 1.63 1.92 2.23 2.79 2.13 1.02 RUNOFF APLTR 12.20 13.37 , actual plant transpiration; APLTR Water Year 1998 Year Water 1999 Year Water .26 .13 .09 .29 .75 .17 .06 .06 .15 .59 than sum of evaporation and transpiration components, as discussed in report); in report); as discussed components, transpiration and of evaporation than sum 0.47 2.01 2.38 3.15 3.28 3.59 2.32 0.68 1.63 1.95 2.44 3.34 2.76 2.21 PPLTR 18.72 16.06 ughfall data are used); ughfall .66 .87 .97 .73 .91 .74 .50 .10 .00 .00 .00 .28 .96 .97 .83 .85 .75 .80 .69 .25 .00 .00 moisture in excess of availabl of moisture in excess 0.03 5.50 0.00 6.38 throughfall where land use is not evergreen forest; where throughfall land use is not evergreen RECHRG tential transpiration; All values rounded to two significant figures. Because of roundin of Because figures. significant rounded to two values All – (available water-holding capacity + specific yield - starting capacity +so specific water-holding – (available .06 .09 .21 .03 .19 .06 .08 .03 .04 .01 .01 .14 .21 .19 .09 .09 .05 .02 .04 .02 .02 .01 0.06 0.87 0.05 0.94 RUNOFF land cover for whichland cover thro , potential evapotranspiration less be (may evapotranspiration potential , .53 .32 .38 .64 .42 .32 .33 .56 1.13 1.53 2.93 3.38 4.19 4.54 4.82 3.17 1.19 1.40 2.53 3.05 3.63 4.67 3.80 2.99 , foliage-type-dependent po foliage-type-dependent , POTET ughfall, and DPM-simulatedughfall, 27.56 24.90 POTET PPLTR .78 .51 .41 .31 4.41 2.16 2.44 4.07 1.47 3.90 1.25 2.59 1.32 2.21 4.57 4.35 4.03 2.88 3.04 1.65 3.23 2.40 1.43 1.04 PRECP 25.31 31.14 Year Year 1997 1997 1997 1998 1998 1998 1998 1998 1998 1998 1998 1998 1998 1998 1998 1999 1999 1999 1999 1999 1999 1999 1999 1999 . 12170315 Station Gaging basin, study Island Whidbey northern the for summaries water-budget computed annual and Monthly . 12170315— Station Gaging basin, study Island Whidbey northern the for summaries water-budget computed annual and Monthly , if the following is negative: rain + snowmelt + starting rain soil + snowmelt , is negative: if the following , measured precipitation; DATE Month Month Totals Totals PRECP October November December January February March April May June July August September October November December January February March April May June July August September inches of water except AVTMP, which is in degrees Fahrenheit. Fahrenheit. which is in degrees AVTMP, inches of except water values] monthly computedprecipitation from input thro + snowmelt rain positive: is following if the direct runoff; Table A3 Table [ below the root zone (recharge); the root zone (recharge); below in moisture stored on foliage (zero for cells with DEFCIT Table A3 Table

38 Estimating Ground-Water Recharge from Precipitation on Whidbey and Camano Islands, Island County, Washington, Water Years 1998 and 1999 .00 .29 .46 .35 .00 .00 -.03 -.01 -.02 -.01 -.01 0.99 -0.04 46.2 42.8 37.3 38.6 40.5 40.7 41.7 47.9 53.1 55.9 55.4 50.1 45.9 Continued .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 0.00 0.00 .71 .69 .60 .51 .38 .42 .26 .16 0.95 1.02 1.05 1.23 7.97 .21 -.04 -.35 -.46 1.79 1.90 1.21 1.43 -1.77 -1.66 -1.65 -1.03 -0.41 .22 .09 .08 .22 .67 .66 0.54 1.82 2.05 2.45 2.48 1.53 12.79 .22 .09 .08 .22 .67 0.57 1.82 2.16 2.80 3.31 3.18 2.27 17.39 Average monthly values Average northern Whidbey Island study basin, Gaging Station 12170315— Station Gaging basin, study Island Whidbey northern .47 .92 .97 .78 .88 .74 .65 .39 .12 .00 .00 0.02 5.94 .10 .15 .20 .06 .14 .06 .05 .04 .03 .02 .01 0.05 0.90 .47 .32 .36 .60 1.16 1.46 2.73 3.22 3.91 4.60 4.31 3.08 26.23 .78 .36 3.31 3.37 3.40 4.05 2.18 3.47 1.45 2.91 1.59 1.38 28.23 . for the summaries water-budget computed annual and Monthly DATE PRECP POTET RUNOFF RECHRG PPLTR APLTR CHGSM EVINT CHGSNW AVTMP DEFCIT Month October November December January February March April May June July August September To tals Table A3

Appendix A 39 .00 .00 .00 .00 .00 .00 .15 .06 .01 .00 .00 .00 .00 -.04 -.02 -.07 -.03 -.04 -.01 -.06 -.02 -.01 , change 0.00 0.12 -0.10 -0.31 DEFCIT , interception , average , average CHGINT EVINT AV T M P 46.4 40.5 36.6 37.5 40.8 40.5 41.4 48.5 50.8 54.3 51.8 47.9 44.8 43.2 42.7 36.0 37.9 38.0 38.0 38.2 44.4 52.5 53.4 54.8 47.5 43.9 AV T M P direct runoff – recharge. – recharge. direct runoff ; soil water that percolates; soil water Continued ation and transpiration components RECHRG .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 0.00 0.00 0.00 0.00 CHGSNW as discussed in report); , change in snowpack; , change in soil moisture;, .34 .31 .46 .41 .69 .37 .35 .40 .30 .01 .22 .40 .49 .46 .77 .75 .47 .63 .67 .37 .37 .10 0.72 4.59 0.37 5.83 EVINT use of rounding totals may not exactly equal the sum of use of rounding totals may not exactly CHGSM CHGSNW starting soil moisture) – measured .93 .71 .99 .20 .54 -.67 -.89 -.88 -.11 -.10 -.70 -.61 1.94 0.42 2.20 1.91 1.23 2.17 0.19 e water-holding capacity – evapor – capacity e water-holding -1.74 -1.66 -0.63 -1.56 -1.24 -2.28 -1.24 d transpiration components, CHGSM ; measured or estimated direct runoff; .11 .03 .03 .16 .56 .88 .27 .08 .02 .03 .05 .38 .64 0.30 1.76 2.06 2.29 1.97 0.50 1.35 1.61 2.05 2.71 1.48 APLTR 10.43 10.90 , actual plant transpiration; RUNOFF APLTR Water Year 1998 Year Water 1999 Year Water rounded to two significant figures. Beca figures. significant two to rounded .11 .03 .03 .16 .56 .08 .02 .03 .05 .38 0.30 1.77 2.09 2.63 2.87 3.33 2.01 0.58 1.35 1.62 2.07 3.00 2.36 1.97 than sum of evaporation an than sum of evaporation PPLTR 15.90 13.51 moisture in excess of availabl of moisture in excess .04 .20 .46 .50 .64 .37 .00 .00 .00 .00 .00 .01 .16 .59 .64 .69 .60 .51 .27 .20 .01 .00 0.00 2.21 0.00 3.68 RECHRG simulated throughfall where land use is not evergreen forest; where land throughfall use is not evergreen simulated + snowmelt – (available water-holding capacity yield - + specific water-holding – (available + snowmelt .07 .09 .45 .12 .33 .16 .07 .03 .04 .01 .00 .09 .22 .46 .45 .35 .17 .06 .03 .06 .02 .01 0.10 1.48 0.00 1.93 RUNOFF which is in degrees Fahrenheit. All values which is in degrees , potential evapotranspiration (may be less (may potential evapotranspiration , .47 .31 .35 .57 .39 .31 .33 .54 1.00 1.35 2.63 3.09 3.82 4.01 4.37 2.85 1.10 1.26 2.27 2.77 3.36 4.28 3.43 2.69 , foliage-type-dependent potential transpiration; POTET 24.83 22.72 POTET PPLTR ipitation throughfall, ipitationand DPM- throughfall, zero for cells with land cover for data arewhich used); throughfall zero for cells with land cover .91 .01 .38 .64 .13 2.98 1.46 1.32 2.43 1.43 2.75 1.74 1.04 1.38 1.30 2.74 2.77 2.81 4.21 2.12 1.04 2.10 1.78 1.06 17.83 22.70 PRECP , if the following is negative: rain + snowmelt + starting soil rain + snowmelt , is negative: if the following Year Year 1997 1997 1997 1998 1998 1998 1998 1998 1998 1998 1998 1998 1998 1998 1998 1999 1999 1999 1999 1999 1999 1999 1999 1999 DEFCIT . 12170320— Station Gaging Island Whidbey basin, Cove study Penn the for summaries water-budget computed annual and Monthly . 12170320 Station Gaging Island Whidbey basin, study Cove Penn the for summaries water-budget computed annual and Monthly DATE , measured precipitation; Month Month Totals Totals October November December January February March April May June July August September October November December January February March April May June July August September PRECP Table A4 loss loss computed from input prec – measured direct runoff; if the following is positive: rain is positive: – measured if the following direct runoff; AVTMP, in inches except of water All values temperature; the shown monthly values] monthly the shown below the root zone (recharge); below in moisture stored on foliage ( Table A4 [

40 Estimating Ground-Water Recharge from Precipitation on Whidbey and Camano Islands, Island County, Washington, Water Years 1998 and 1999 .00 .08 .03 .00 -.05 -.02 -.03 -.01 -.02 -.01 0.00 -0.05 -0.09 44.8 41.6 36.3 37.7 39.4 39.3 39.8 46.4 51.7 53.9 53.3 47.7 44.3 Continued .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 0.00 0.00 .37 .40 .46 .59 .72 .42 .49 .54 .33 .19 .16 0.54 5.21 .22 -.69 -.36 1.18 1.56 1.31 1.11 1.19 -1.65 -1.45 -1.59 -1.06 -0.22 .10 .03 .03 .10 .47 .46 0.40 1.56 1.83 2.17 2.34 1.18 10.66 .10 .03 .03 .10 .47 0.44 1.56 1.85 2.35 2.94 2.84 1.99 14.70 Average monthly values Average .02 .18 .53 .57 .66 .49 .26 .14 .10 .01 .00 0.00 2.94 .08 .16 .46 .28 .34 .17 .06 .03 .05 .02 .00 0.05 1.70 .43 .31 .34 .55 1.05 1.31 2.45 2.93 3.59 4.15 3.90 2.77 23.77 .98 .33 .26 2.14 2.10 2.05 2.62 2.82 2.44 1.92 1.41 1.22 20.27 . Monthly and annual computed water-budget summaries for the Penn Cove study basin, Whidbey Island Gaging Station 12170320— DATE PRECP POTET RUNOFF RECHRG PPLTR APLTR CHGSM EVINT CHGSNW AVTMP DEFCIT Month October November December January February March April May June July August September Totals Table A4

Appendix A 41 .00 .00 .04 .02 .18 .00 .00 .19 .01 .23 .00 .00 .00 .00 ; -.11 -.08 -.02 -.01 -.04 -.01 -.01 -.01 0.25 -0.19 -0.17 -0.11 DEFCIT , actual plant RUNOFF APLTR AV T M P 51.2 46.4 41.4 41.2 45.3 46.3 48.8 54.2 58.4 64.7 62.5 58.8 51.6 50.6 46.5 39.5 41.9 42.7 44.0 46.7 51.2 56.9 59.8 61.9 56.9 49.9 Continued .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 0.00 0.00 0.00 0.00 CHGSNW + starting soil moisture in excess of available of available excess soil moisture in + starting simulated throughfall where land use is not simulated throughfall .73 .81 .77 .93 .79 .51 .11 .73 .30 .91 .48 .54 .78 .37 .39 .12 1.19 1.89 1.04 9.81 1.47 1.65 1.31 1.94 1.59 EVINT 11.56 grees Fahrenheit. All values rounded to two significant significant rounded to two values All grees Fahrenheit. + snowmelt – (available water-holding capacity + specific water-holding – (available + snowmelt .41 .26 .20 .02 .21 .10 .37 -.36 -.18 -.71 -.01 -.36 -.48 -.17 -.46 -.30 2.39 1.22 1.84 2.61 , foliage-type-dependent potential transpiration; -2.19 -1.69 -0.63 -1.64 -1.81 -0.09 CHGSM PPLTR ation and transpiration components, as discussed in report); in report); as discussed components, and transpiration ation .29 .10 .04 .29 .81 .43 .27 .15 .09 .11 .12 .70 .42 0.47 1.96 2.02 2.23 1.12 0.67 1.74 1.94 2.02 2.66 1.18 APLTR 10.01 11.80 the following is positive: rain is positive: the following , if the following is negative: rain + snowmelt snowmelt rain + is negative: , if the following Water Year 1998 Year Water 1999 Year Water om input precipitation throughfall, and DPM- and throughfall, precipitation om input .29 .10 .04 .29 .81 .15 .09 .11 .12 .70 0.47 2.06 2.26 2.85 3.53 3.39 2.29 0.67 1.77 1.99 2.12 3.17 2.64 2.19 PPLTR 18.37 15.74 es of water except AVTMP, which is in de AVTMP, es of except water us Creek study basin, Whidbey Island, Gaging Station 12170400— Station Gaging Island, Whidbey basin, us Creek study DEFCIT .90 .96 .90 .98 .60 .02 .00 .00 .00 .00 .83 .95 .65 .59 .02 .04 .00 .00 0.23 1.37 5.96 0.03 1.14 1.08 1.29 6.62 RECHRG – measured direct runoff; if – measured direct runoff; , average temperature; , average , interception loss computed frcomputed, interception loss .29 .45 .49 .82 .29 .26 .08 .02 .00 .01 .73 .90 .36 .19 .05 .03 .01 0.37 1.25 4.32 0.21 1.18 1.21 1.93 0.01 6.82 RUNOFF AV T M P EVINT ; soil water that percolates below the root zone (recharge); zone (recharge); the root that percolates below ; soil water actly equal the sum of the shown monthly values] actly equal the of the shown sum ect runoff – recharge. All values in inch values All – recharge. ect runoff , potential evapotranspiration (may be less than sum of evapor of be sum than less (may , potential evapotranspiration .61 .35 .42 .75 .41 .31 .34 1.23 1.72 3.14 3.44 4.22 4.93 4.88 3.28 1.14 0.53 1.53 2.78 3.17 3.53 4.64 3.93 3.10 POTET 28.97 25.42 RECHRG POTET , change in snowpack; , change in snowpack; .51 .59 .24 4.47 2.62 2.58 5.81 2.66 3.47 1.59 2.80 1.06 1.15 4.12 5.20 4.45 3.81 5.89 3.77 1.59 2.78 2.70 1.29 1.11 PRECP 29.31 36.95 , change in soil moisture; CHGSNW Year Year 1997 1997 1997 1998 1998 1998 1998 1998 1998 1998 1998 1998 1998 1998 1998 1999 1999 1999 1999 1999 1999 1999 1999 1999 CHGSM . Monthly and annual computed water-budget summaries for the Cultus Creek study basin, Whidbey Island, Gaging Station 12170400 . Cult the for summaries water-budget computed annual and Monthly DATE , measured precipitation; Month Month Totals Totals PRECP October November December January February March April May June July August September October November December January February March April May June July August September figures. Because of rounding totals may not ex not may totals rounding of Because figures. measured or estimated direct runoff; measured or estimatedrunoff; direct transpiration; evergreen forest; evergreen components transpiration and – evaporation capacity water-holding dir – measured soil moisture) yield - starting Table A5 [ Table A5

42 Estimating Ground-Water Recharge from Precipitation on Whidbey and Camano Islands, Island County, Washington, Water Years 1998 and 1999 .09 .02 .12 .09 .00 -.02 -.06 -.04 -.01 -.01 -.01 0.04 -0.15 50.9 46.5 40.4 41.6 44.0 45.2 47.7 52.7 57.6 62.3 62.2 57.8 50.8 Continued .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 0.00 0.00 .82 .70 .67 .65 .24 .56 .21 1.33 1.23 1.60 1.36 1.32 10.68 .66 .29 -.36 -.33 -.93 -.23 -.14 2.12 1.51 0.23 -1.91 -1.26 -0.36 .22 .10 .07 .21 .75 .81 .34 0.57 1.85 1.98 2.13 1.89 10.91 .22 .10 .07 .21 .75 0.57 1.92 2.13 2.48 3.35 3.01 2.24 17.05 Average monthly values Average us Creek study basin, Whidbey Island, Gaging Station 12170400— Station Gaging Island, Whidbey basin, us Creek study .87 .96 .62 .31 .01 .02 .00 .00 0.13 1.05 1.23 1.09 6.29 .51 .81 .86 .33 .22 .06 .03 .01 .01 0.29 1.23 1.21 5.57 .51 .33 .38 .64 1.19 1.62 2.96 3.30 3.88 4.78 4.41 3.19 27.19 .90 .42 4.30 3.91 3.52 4.81 4.28 3.62 1.59 2.79 1.88 1.13 33.13 . Cult the for summaries water-budget computed annual and Monthly DATE PRECP POTET RUNOFF RECHRG PPLTR APLTR CHGSM EVINT CHGSNW AVTMP DEFCIT Month October November December January February March April May June July August September Totals Table A5

Appendix A 43 ; .00 .00 .00 -.36 -.15 -.07 -.25 -.31 -.60 -.43 -.30 -.19 -.03 -.37 -.39 -.10 -.90 -.62 -.62 -.68 -.04 -.04 -0.52 -3.21 -0.33 -4.12 DEFCIT , actual plant RUNOFF Continued APLTR 47.2 41.5 37.4 38.1 41.5 41.5 42.7 49.5 52.1 56.1 53.7 49.8 46.0 44.5 43.4 36.6 38.6 38.8 39.1 39.6 45.5 53.2 54.5 56.0 49.1 44.9 AV T M P 12170440 n 12170440— n .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 0.00 0.00 0.00 0.00 CHGSNW tential transpiration; + starting soil moisture in excess of available of available starting moisture in excess soil + simulated throughfall where land use is not .65 .62 .69 .99 .57 .47 .23 .20 .08 .60 .38 .44 .63 .29 .27 .07 1.15 1.73 1.04 8.41 0.84 1.22 1.36 1.79 1.56 9.44 EVINT components, as discussed in report); in report); as discussed components, rees Fahrenheit. All values rounded to two significant significant rounded to two rees Fahrenheit. All values snowmelt – (available water-holding capacity + specific capacity + specific water-holding – (available snowmelt .63 .01 .20 .41 .06 , foliage-type-dependent po foliage-type-dependent , -.31 -.44 -.49 2.69 1.45 1.48 2.99 1.96 1.01 0.29 -0.17 -1.20 -1.83 -1.70 -1.08 -1.73 -1.16 -1.13 -2.12 -1.68 -1.04 CHGSM PPLTR tion and transpirationtion and .23 .08 .04 .29 .64 .50 .19 .08 .09 .15 .53 0.42 1.70 2.05 2.58 2.42 1.36 0.67 1.61 1.86 2.08 2.95 2.17 1.11 APLTR 12.29 13.46 except AVTMP, which is in deg AVTMP, except , if the following is negative: rain + snowmelt snowmelt rain + is negative: , if the following Water Year 1998 Year Water 1999 Year Water om input precipitation and throughfall, DPM- .23 .08 .04 .29 .64 .19 .08 .09 .15 .53 0.42 1.70 2.05 2.58 2.85 3.11 2.09 0.68 1.61 1.86 2.08 2.95 2.35 1.98 than sum of evapora PPLTR 16.07 14.53 DEFCIT .00 .40 .79 .47 .44 .03 .00 .00 .00 .00 .00 .00 .08 .66 .77 .85 .14 .05 .00 .00 .00 .00 e shown monthly values] e shown easured direct runoff; if the following is positive: rain + is positive: if the following easured direct runoff; 0.00 2.14 0.00 2.54 RECHRG All values in inches of water in inches of water All values , average temperature;, average , interception loss computed fr .36 .37 .68 .43 .30 .19 .03 .00 .37 .51 .69 .62 .68 .04 .04 0.52 2.83 1.18 1.14 8.03 0.33 1.22 2.32 1.81 1.20 9.85 RUNOFF AV T M P EVINT ; soil water that percolates below the root zone (recharge); the root zone (recharge); that percolateswater ; soil below actly equal the sum of th .49 .32 .37 .61 .40 .31 .33 .56 , potential evapotranspiration (may be less , potential evapotranspiration 1.04 1.47 2.82 3.15 3.86 4.08 4.39 2.92 1.13 1.37 2.49 2.90 3.35 4.26 3.43 2.77 25.51 23.28 POTET RECHRG POTET .95 .48 .14 .75 .14 , change in snowpack; 4.26 2.33 1.96 5.19 2.40 3.15 1.60 2.31 1.21 2.99 3.77 3.47 4.26 5.43 3.59 1.30 2.48 2.22 1.11 PRECP 25.98 31.51 , change in soil moisture; , CHGSNW Year Year 1997 1997 1997 1998 1998 1998 1998 1998 1998 1998 1998 1998 1998 1998 1998 1999 1999 1999 1999 1999 1999 1999 1999 1999 CHGSM . Monthly and annual computed water-budget summaries for the South Whidbey State Park study basin, Whidbey Island Gaging Station . Statio Gaging Island Whidbey basin, study Park State Whidbey South the for summaries water-budget computed annual and Monthly DATE , measured precipitation; Month Month Totals Totals PRECP October November December January February March April May June July August September October November December January February March April May June July August September evergreen forest; evergreen – m components and transpiration capacity –evaporation water-holding transpiration; yield – starting soil moisture) – measured –recharge. direct runoff Because of rounding totals may not figures. ex measured or estimated direct runoff; runoff; direct estimated or measured Table A6 [ Table A6

44 Estimating Ground-Water Recharge from Precipitation on Whidbey and Camano Islands, Island County, Washington, Water Years 1998 and 1999 -.37 -.27 -.09 -.12 -.15 -.75 -.53 -.46 -.44 -.04 -.02 -0.43 -3.66 Continued 45.8 42.4 37.0 38.4 40.2 40.3 41.1 47.5 52.7 55.3 54.8 49.4 45.4 n 12170440— n .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 0.00 0.00 .62 .92 .69 .50 .55 .26 .23 .07 0.99 1.54 1.24 1.30 8.93 .42 .21 -.48 -.12 -.74 2.09 2.22 1.29 -1.16 -1.16 -1.91 -1.38 -0.72 .21 .08 .06 .22 .58 .81 0.54 1.65 1.96 2.33 2.68 1.76 12.88 .21 .08 .06 .22 .58 0.55 1.65 1.96 2.33 2.90 2.73 2.03 15.30 Average monthly values Average .00 .24 .73 .62 .64 .08 .02 .00 .00 .00 .00 0.00 2.34 .37 .44 .94 .56 .46 .44 .04 .02 0.43 2.02 1.75 1.48 8.94 .45 .31 .35 .58 1.08 1.42 2.66 3.02 3.60 4.17 3.91 2.84 24.40 .62 .14 3.63 3.05 2.72 4.73 3.92 3.37 1.45 2.40 1.72 1.03 28.75 . Statio Gaging Island Whidbey study basin, Park State Whidbey South the for summaries water-budget computed annual and Monthly DATE PRECP POTET RUNOFF RECHRG PPLTR APLTR CHGSM EVINT CHGSNW AVTMP DEFCIT Month October November December January February March April May June July August September Totals Table A6

Appendix A 45 , , .08 .10 .56 .46 .51 .10 .19 .26 .44 .90 .78 .24 .04 -.08 -.21 -.24 -.31 -.21 -.11 -.25 -.21 -.20 0.13 0.88 0.04 2.13 EVINT SYM-RO ACTSEV 53.4 48.8 43.7 43.6 47.6 48.7 51.2 56.7 60.2 64.9 64.4 60.6 53.7 52.4 48.7 41.8 43.4 43.6 46.5 49.7 54.6 62.1 63.7 64.0 59.8 52.6 AVTMP , average temperature] , average , change in moisture stored on .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 AV T M P 0.00 0.00 0.00 0.00 , change in soil moisture; change , CHGSNW CHGINT CHGSM .50 .47 .60 .77 .45 .41 .27 .10 .14 .59 .88 .46 .61 .69 .36 .35 .11 0.98 1.07 1.00 6.77 0.72 1.14 1.20 1.15 8.27 EVINT AND CAMANO ISLANDS , change in snowpack; , change in snowpack; .77 .62 .04 .13 .96 -.36 -.71 -.21 -.45 -.49 -.72 -.92 -.55 2.24 1.31 1.19 2.21 1.19 1.07 0.20 -1.85 -1.44 -1.06 -0.54 -1.77 -1.52 CHGSM CHGSNW .26 .09 .06 .24 .73 .83 .30 .14 .03 .06 .10 .63 .61 , soil water that percolates below the root zone (recharge); the percolatesbelow that , soil water 0.41 1.92 1.90 2.11 1.78 0.60 1.76 1.84 1.99 2.27 1.31 , actual plant transpiration; 10.63 11.32 APLTR forest; forest; components, as discussed in report); in report); as discussed components, APLTR RECHRG .26 .09 .06 .24 .73 .14 .03 .06 .10 .63 0.41 2.02 2.36 3.00 3.44 3.76 2.46 0.70 1.83 2.03 2.39 3.45 2.71 2.36 Continued 18.84 16.42 PPLTR .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 0.00 0.00 0.00 0.00 SNWEVP tion and transpirationtion and Water Year 1998 Year Water 1999 Year Water SUMMARIES FOR WHIDBEY .04 .02 .03 .05 .12 .22 .23 .28 .30 .33 .22 .03 .02 .03 .04 .12 .21 .23 .25 .32 .25 .21 0.09 1.94 0.09 1.80 ACTSEV roughfall where land use is not evergreen evergreen is not use where land roughfall , measuredestimated or direct runoff; than sum of evapora .44 .57 .85 .38 .12 .04 .01 .00 .00 .60 .94 .92 .41 .33 .09 .03 .01 .00 0.16 1.59 1.03 5.18 0.02 1.31 1.56 6.24 RECHRG , foliage-type-dependent potential transpiration; RUNOFF PPLTR .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 0.00 0.00 0.00 0.00 RUNOFF .01 .02 .00 .00 .00 .00 .00 .02 .00 .00 .00 .00 .00 .00 .00 .00 -.01 -.01 -.01 -.01 -.01 -.01 0.01 0.00 0.00 0.00 CHGINT pitation and DPM-simulatedthroughfall, th , potential evapotranspiration (may be less , potential evapotranspiration .60 .35 .40 .71 .44 .32 .34 .58 , direct evaporation of snow; snow; of direct evaporation , 1.21 1.69 3.24 3.57 4.41 4.86 5.16 3.48 1.28 1.56 2.94 3.36 3.87 4.97 4.01 3.32 for which throughfall data are used);data are for which throughfall 29.68 26.98 POTET POTET SNWEVP .24 .24 .80 .18 4.03 2.10 1.87 4.63 2.26 3.52 1.53 2.27 1.20 1.06 2.68 3.77 3.59 3.80 4.76 3.16 1.31 2.56 2.20 1.22 24.93 30.03 PRECP Year Year 1997 1997 1997 1998 1998 1998 1998 1998 1998 1998 1998 1998 1998 1998 1998 1999 1999 1999 1999 1999 1999 1999 1999 1999 . Monthlyand annual computedwater-budget summaries forWhidbeyIsland, Island County, Washington . Monthlyand annual computedwater-budget summaries for WhidbeyIsland, Island County, Washington— DATE , measured precipitation; Month Month Totals Totals PRECP October November December January February March April May June July August September October November December January February March April May June July August September APPENDIX B.APPENDIX WATER-BUDGET MONTHLY COMPUTER Table B1 [ foliage (zero for cells with land cover actual bare-soil evaporation; evaporation; bare-soil actual interception loss computed from input preci Table B1

46 Estimating Ground-Water Recharge from Precipitation on Whidbey and Camano Islands, Island County, Washington, Water Years 1998 and 1999 .13 .18 .50 .68 .64 .17 -.02 -.16 -.24 -.26 -.20 0.09 1.50 52.9 48.8 42.8 43.5 45.6 47.6 50.5 55.6 61.2 64.3 64.2 60.2 53.1 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 0.00 0.00 .54 .81 .98 .90 .61 .53 .55 .31 .23 .12 0.85 1.08 7.52 .90 .50 -.16 -.42 -.82 1.72 1.49 1.19 -1.81 -1.08 -1.29 -0.17 -038 .20 .06 .06 .17 .68 .45 0.50 1.84 1.87 2.05 2.02 1.07 10.97 .20 .06 .06 .17 .68 0.55 1.93 2.19 2.70 3.45 3.23 2.41 Continued 17.63 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 0.00 0.00 Average monthly values Average .04 .02 .03 .05 .12 .22 .23 .27 .31 .29 .22 0.09 1.87 .52 .75 .97 .40 .22 .07 .02 .01 .00 0.09 1.45 1.21 5.71 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 0.00 0.00 000 .01 .00 .00 .01 .00 .00 .00 .00 .00 -.01 -.01 0.00 0.00 .52 .33 .37 .65 1.25 1.62 3.09 3.46 4.14 4.91 4.59 3.40 28.33 .52 .21 3.36 2.93 2.73 4.21 3.51 3.34 1.42 2.41 1.70 1.14 27.48 PRECP POTET CHGINT RUNOFF RECHRG ACTSEV SNWEVP PPLTR APLTR CHGSM EVINT CHGSNW AVTMP SYM-RO . Washington— County, Island Island, Whidbey for summaries water-budget computed annual and Monthly DATE Month October November December January February March April May June July August September Totals Table B1 Table

Appendix B 47 , , .02 .05 .46 .45 .53 .24 .03 .07 .15 .39 .72 .72 .30 .08 .00 -.02 -.03 -.05 -.03 -.03 -.03 -.03 0.04 1.67 0.01 2.34 EVINT SYM-RO ACTSEV 53.5 48.9 43.8 43.7 47.7 48.8 51.3 56.8 60.3 64.9 64.4 60.6 53.8 52.4 48.8 41.9 43.4 43.7 46.6 49.8 54.7 62.4 63.9 64.1 59.9 52.7 AVTMP , average , average , change in moisture stored on .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 0.00 0.00 0.00 0.00 AV T M P , change in soil moisture; CHGSNW CHGINT .55 .59 .68 .91 .45 .46 .32 .06 .17 .66 .97 .48 .61 .69 .40 .38 .14 CHGSM 1.06 1.15 1.12 7.52 0.80 1.30 1.13 1.25 8.82 EVINT .91 .90 .03 .14 .62 -.30 -.20 -.52 -.35 -.78 -.68 , change in snowpack; , change in snowpack; 2.47 1.20 1.23 2.50 1.58 1.24 0.19 -2.05 -1.69 -1.17 -1.04 -0.80 -1.80 -1.80 -1.06 CHGSM discussed in report); .26 .09 .05 .24 .75 .38 .14 .04 .06 .13 .67 .79 CHGSNW 0.42 2.02 2.13 2.47 2.18 1.10 0.64 1.86 2.00 2.22 2.65 1.58 12.09 12.78 , soil water that percolates below , soil thethatwater root zone (recharge); percolates below APLTR , actual plant transpiration; forest; .26 .09 .05 .24 .75 .14 .04 .06 .13 .67 0.43 2.08 2.44 3.04 3.44 3.83 2.51 0.71 1.90 2.10 2.43 3.45 2.73 2.38 APLTR RECHRG 19.16 16.75 PPLTR Continued iration components, as .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 0.00 0.00 0.00 0.00 SNWEVP tential transpiration; .01 .00 .01 .01 .02 .04 .04 .05 .05 .06 .04 .01 .00 .00 .01 .02 .04 .04 .04 .05 .04 .04 Water Year 1998 Year Water 1999 Year Water 0.02 0.34 0.02 0.31 ACTSEV ll where land use is not evergreen ll where land use is not evergreen .01 .00 .01 .01 .02 .05 .04 .05 .05 .06 .05 .01 .00 .00 .01 .02 .04 .04 .04 .05 .05 .05 0.02 0.37 0.02 0.34 , measured or estimated direct runoff; , measured or estimated direct runoff; SOLPEV , foliage-type-dependent po , foliage-type-dependent .40 .55 .51 .10 .03 .01 .00 .00 .58 .90 .53 .38 .04 .01 .01 .00 RUNOFF ay be less than sum of evaporation and transp of evaporation less than sum ay be 0.16 1.63 1.03 1.21 5.63 0.02 1.35 1.43 1.07 6.33 RECHRG PPLTR .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 0.00 0.00 0.00 0.00 hfall, and DPM-simulated throughfa and DPM-simulated hfall, RUNOFF .01 .00 .01 .00 .00 .00 .00 .00 .01 .00 .00 .00 .00 .00 .00 .00 .00 .00 -.01 -.01 -.01 -.01 0.01 0.00 0.00 0.00 CHGINT , potential evapotranspiration (m evapotranspiration , potential .58 .34 .40 .70 .43 .32 .34 .58 , direct evaporation of snow; of snow; evaporation , direct 1.19 1.69 3.25 3.57 4.39 4.81 5.13 3.46 1.27 1.56 2.95 3.36 3.86 4.94 3.97 3.30 29.51 26.88 POTET POTET input precipitation throug SNWEVP .12 .35 .92 .26 4.18 2.16 2.18 4.49 2.46 3.76 1.66 2.45 1.30 1.35 2.72 3.97 3.97 4.00 4.04 3.21 1.41 2.77 2.22 1.28 26.47 30.78 PRECP Year Year 1997 1997 1997 1998 1998 1998 1998 1998 1998 1998 1998 1998 1998 1998 1998 1999 1999 1999 1999 1999 1999 1999 1999 1999 . Washington— County, Island Island, Camano for summaries water-budget computed annual and Monthly . Monthly and annual computed water-budget summaries for Camano Island, Island County, Washington DATE , measured precipitation; Month Month Totals Totals PRECP October November December January February March April May June July August September October November December January February March April May June July August September Table B2 Table Table B2 [ foliage (zero for cells with land cover for whichdata are used); for throughfall cover land foliage (zero for cells with actual bare-soil evaporation; interception loss computed from loss interception temperatureSYM-RO = DPM-simulated direct runoff] temperatureSYM-RO

48 Estimating Ground-Water Recharge from Precipitation on Whidbey and Camano Islands, Island County, Washington, Water Years 1998 and 1999 .05 .10 .42 .58 .62 .27 .06 -.01 -.03 -.04 -.03 0.02 2.00 53.0 48.9 42.9 43.6 45.7 47.7 50.6 55.8 61.3 64.4 64.2 60.3 53.2 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 0.00 0.00 .60 .94 .91 .70 .53 .58 .36 .22 .16 0.93 1.06 1.18 8.17 .33 -.19 -.33 1.85 1.71 1.24 1.22 -1.92 -1.23 -1.49 -1.05 -0.31 -044 .20 .06 .06 .19 .71 .58 0.53 1.94 2.07 2.35 2.41 1.34 12.43 .20 .06 .06 .19 .71 0.57 1.99 2.27 2.74 3.45 3.28 2.44 17.96 Continued .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 0.00 0.00 .01 .00 .01 .01 .02 .04 .04 .05 .05 .05 .04 0.02 0.33 Average monthly values monthly Average .01 .00 .01 .01 .02 .04 .04 .05 .05 .06 .05 0.02 0.35 .49 .72 .52 .24 .04 .01 .00 .00 0.09 1.49 1.23 1.14 5.98 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 0.00 0.00 .01 .00 .00 .00 .00 .00 .00 .00 .00 .00 -.01 0.00 0.00 .51 .33 .37 .64 1.23 1.63 3.10 3.46 4.13 4.88 4.55 3.38 28.20 .52 .31 3.45 3.06 3.07 4.25 3.25 3.49 1.54 2.61 1.76 1.32 28.62 PRECP POTET CHGINT RUNOFF RECHRG SOLPEV ACTSEV SNWEVP PPLTR APLTR CHGSM EVINT CHGSNW AVTMP SYM-RO . Washington— County, Island Island, Camano for summaries water-budget computed annual and Monthly DATE Month October November December January February March April May June July August September Totals Table B2 Table

Appendix B 49 %STIMATING'ROUND 7ATER2ECHARGEFROM0RECIPITATIONON7HIDBEY AND#AMANO)SLANDS 3UMIOKAAND"AUER 72)2n )SLAND#OUNTY 7ASHINGTON 7ATER9EARSAND 6ERSION !UGUST CLEDPAPER Y 0RINTEDONREC