Hydrogeologic Data from a Shallow Flooding

Demonstration Project, Twitchell Island, California,

1997—2001

Prepared in cooperation with the

CALIFORNIA DEPARTMENT OF WATER RESOURCES

U.S. GEOLOGICAL SURVEY

Open-File Report 03-378

Hydrogeologic Data from a Shallow Flooding 

Demonstration Project, Twitchell Island, 

California, 1997–2001

By James M. Gamble, Karen R. Burow, Gail A. Wheeler, Robert Hilditch, and 

Judy Z. Drexler

Sacramento, California

2003

Open-File Report 03-378

U.S. GEOLOGICAL SURVEY

Prepared in cooperation with the

CALIFORNIA DEPARTMENT OF WATER RESOURCES 6217-83
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:

District Chief

U.S. Geological Survey

Placer Hall—Suite2012

6000 J Street

sacramento, CA 95819-6129

http://ca.water.usgs.gov

Copies of this report can be purchased from:

U.S. Geological Survey

Information Services

Building 810

Box 25286, Federal Center

Denver, CO 80225-0286
Contents iii

Contents

Abstract ................................................................................................................................................................ 1

Introduction .......................................................................................................................................................... 1

Purpose........................................................................................................................................................ 3

Study Site .................................................................................................................................................... 3

Data Collection Methods...................................................................................................................................... 5

Soil Coring .................................................................................................................................................. 5

Borehole-Geophysical Data ........................................................................................................................ 6

Monitoring Wells ........................................................................................................................................ 6

Temperature Monitoring ............................................................................................................................. 7

Slug Tests.................................................................................................................................................... 8

Flow Monitoring ......................................................................................................................................... 8

Results .................................................................................................................................................................. 9

Lithologic Characterization......................................................................................................................... 9

Water Levels ............................................................................................................................................... 11

Water Temperatures.................................................................................................................................... 11

Estimates of Hydraulic Conductivity.......................................................................................................... 11

Seepage Estimates....................................................................................................................................... 16

Summary .............................................................................................................................................................. 16

References Cited .................................................................................................................................................. 17
iv Figures

FIGURES

Figure 1. Map showing location of Twitchell Island in the Sacramento–San Joaquin Delta, California ......... 2

Figure 2. Map showing demonstration ponds location and layout ................................................................... 4

Figure 3. Diagram showing conceptualized flow from the demonstration pond to drainage ditch on 

Twitchell Island ................................................................................................................................. 5

Figure 4. Diagram showing Twitchell Island demonstration pond boring locations ........................................ 6

Figure 5. Twitchell Island demonstration pond well locations ......................................................................... 7

Figure 6. Graph showing geologic section and geophysical logs for selected wells on Twitchell Island, 

California ........................................................................................................................................... 10

Figure 7. Graph showing water level response in shallow wells in relation to the San Joaquin 

River stage at Twitchell Island, California ........................................................................................ 12

Figure 8. Graph showing water level in wells at Twitchell Island, California.................................................. 13

Figure 9. Graph showing water temperature in wells on Twitchell Island, California ..................................... 14

Figure 10. Graph showing water budget for East Pond from October 2000 through September 2001 

on Twitchell Island, California .......................................................................................................... 15
Tables v

TABLES

Table 1. Well construction details for wells on Twitchell Island, California .................................................. 18

Table 2. Ground-water elevations on Twitchell Island, California, From Setpember 1997 to 

September 2001 ................................................................................................................................. 19

Table 3. Well construction and estimates of hydraulic conductivity and transmissivity from slug tests 

for selected wells on Twitchell Island, California ............................................................................. 25

Table 4. Daily mean inflow at eastern inlet of East Pond at USGS site number 380626121383806 

on Twitchell Island, California .......................................................................................................... 26

Table 5. Daily mean inflow at western inlet of East Pond at USGS site number 380626121383807 

on Twitchell Island, California .......................................................................................................... 29

Table 6. Daily mean outflow at eastern outlet of East Pond at USGS site number 380626121383802 

on Twitchell Island, California .......................................................................................................... 32

Table 7. Daily mean outflow at western outlet of East Pond at USGS site number 380626121383801 

on Twitchell Island, California .......................................................................................................... 36

Table 8. Water budget for East Pond, October 2000 to September 2001, on Twitchell Island....................... 40
vi Conversion Factors, Vertical Datum, Abbreviations, and Acronyms

CONVERSION FACTORS, VERTICAL DATUM, ABBREVIATIONS, AND 

ACRONYMS

CONVERSION FACTORS

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F = (1.8 × °C) + 32

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 (NAVD 

88).

ABBREVIATIONS AND ACRONYMS

CIMIS California Irrigation Management Information System

DOC dissolved organic carbon

DWR (California) Department of Water Resources

EM electromagnetic

ET evapotranspiration

HPIA hydrophilic acid

NWIS National Water Information System

PVC polyvinyl chloride

TDS total dissolved solids

THM trihalomethane

THMFP trihalomethane formation potential

USGS U.S. Geological Survey

c/s counts per second

mS/m millisiemens per meter

Multiply By To obtain

acre 0.4047 hectare

acre-foot (acre-ft) 0.001233 cubic hectometer 

cubic foot (ft3) 0.02832 cubic meter 

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

gallon (gal) 3.785 liter

gallon per minute (gal/min) 0.06309 liter per second

inch (in.) 2.54 centimeter

inch per hour (in/hr) 2.54 centimeter per hour

inch per year (in/yr) 2.54 centimeter per year

square foot (ft2) 0.09290 square meter

square inch (in2) 6.452 square centimeter
Introduction 1

Hydrogeologic Data from a Shallow Flooding 

Demonstration Project, Twitchell Island, California, 

1997–2001

By James M. Gamble, Karen R. Burow, Gail A. Wheeler, Robert Hilditch, and Judy Z. Drexler

ABSTRACT

Data were collected during a study to 

determine the effects of continuous shallow 

flooding on ground-water discharge to an 

agricultural drainage ditch on Twitchell Island, 

California. The conceptual model of the 

hydrogeologic setting was detailed with soil 

coring and borehole-geophysical logs. Twenty-two 

monitoring wells were installed to observe 

hydraulic head. Ten aquifer slug tests were done in 

peat and mineral sediments. Ground-water and 

surface-water temperature was monitored at 14 

locations. Flow to and from the pond was 

monitored through direct measurement of flows 

and through the calculation of a water budget. 

These data were gathered to support the 

development of a two-dimensional ground-water 

flow model. The model will be used to estimate 

subsurface discharge to the drainage ditch as a 

result of the pond. The estimated discharge will be 

used to estimate the concentrations of DOC that 

can be expected in the ditch. 

INTRODUCTION

Dissolved organic carbon (DOC) originating in 

the Sacramento-San Joaquin Delta (Delta) is 

increasingly present in water transferred to southern 

California. The DOC may form trihalomethanes 

(THMs) at concentrations that exceed the U.S. 

Environmental Protection Agency’s limit of 0.100 

milligrams per liter in drinking water (U.S. 

Environmental Protection Agency, 2002) when the 

water is chlorinated (Fujii and others, 1998). Drinking 

water for two-thirds of California’s population of more 

than 20 million people passes through the Delta 

(California Department of Water Resources, 1993). 

The Delta is a 738,000-acre tidal marsh of islands and 

interlaced channels that has been developed for 

agricultural use (fig. 1). Agricultural practices 

throughout the Delta promote the dissolution and 

flushing of carbon from peat beds through the 

decomposition (microbial oxidation) of organic matter. 

In addition to eluting DOC from the peat, the 

decomposition of organic matter causes land 

subsidence. As a result of subsidence, many of the 

Delta islands that once were at sea level now lie as deep 

as 20 feet (ft) below sea level. As the surface subsides, 

pumping from the agricultural drainage ditches is 

increased to maintain arable land. More aggressive 

pumping increases the proportion of drainage ditch 

water (and DOC) in Delta surface waters and increases 

the hydraulic pressure on the levee system. The 

increased pressure could increase the chances of levee 

failure.

From 1980 to 1981, approximately 7.8 million 

acre-feet of the surface water flowing through the Delta 

was diverted to water purveyors for drinking, 

municipal, and agricultural purposes (California 

Department of Water Resources, 1993). Organic 

carbon in the peat is dissolved and then transferred to 

the surface water through the island drainage systems. 

Island drainage water is a combination of irrigation 

water that seeps through the peat or flows overland 

across the peat, direct precipitation, and ground-water 

discharge through the peat. The drainage water is 

pumped from the islands into adjacent rivers and 

sloughs.
2 Hydrogeologic Data from a Shallow Flooding Demonstration Project, Twitchell Island, California, 1997–2001

Coast Range

Study Area

5

5

10 Miles

10 Kilometers

0

0

121°45' 121°30'

38°

30'

38°

15'

38°

00'

37°

45'

Twitchell Island

CALIFORNIA

Figure 1. Location of Twitchell Island in the Sacramento–San Joaquin Delta, California.
Introduction 3

Because of the increased probability of levee 

failure caused by subsidence, the cause and prevention 

of land subsidence has been a concern in the Delta 

since the 1920’s and has been the subject of several 

studies. Collectively, the studies show that subsidence 

occurs almost exclusively in the peat layer (Rojstaczer 

and others, 1991) at an average rate of 3 inches per year 

(Weir, 1950; Rojstaczer and others, 1991). These 

studies also show that draining and cultivating the 

islands creates a surface environment that promotes the 

microbial oxidation of the peat (Deverel and 

Rojstaczer, 1996; Deverel and others, 1998).

Microbial digestion of organic matter in the 

aerobic environment of the unsaturated zone and the 

anaerobic environment of the saturated zone liberates 

carbon to the aqueous phase, generating DOC and 

causing loss in land elevation. Differences in metabolic 

processes between the oxygen-rich and oxygen-poor 

environments produce varying proportions of different 

forms of DOC in the saturated and unsaturated zones. 

For example, Deverel and others (1998) and Fujii and 

others (1998) found that greater concentrations of the 

hydrophilic acid (HPIA) variety of DOC were present 

in the aerobic environment of the peat and that the 

anaerobic zone had relatively less of the HPIA form. 

Fujii and others (1998) demonstrated that the different 

varieties of DOC have different THM formation 

potential (THMFP).

Current Delta management practices change the 

environment in the peat through the course of a year, 

promoting or inhibiting microbial oxidation through 

the cyclical wetting and draining of the upper few feet 

of the peat. In general, moisture contents near and 

equal to saturation, combined with low temperatures, 

inhibit microbial oxidation of the peat (Deverel and 

Rojstaczer, 1996). The oxidation-limiting role of 

saturation and its accompanying anaerobic conditions 

were observed by Miller and others (2000), who found 

that perennial flooding as shallow as 35 centimeters 

(13.8 inches) produced anaerobic conditions and a net 

gain of organic material in a small test plot. Perennial 

shallow flooding currently is seen as a promising 

technique to alleviate subsidence and possibly to 

recover some land-surface elevation. However, the 

effect of shallow flooding on DOC loading to the 

drainage ditches is unclear.

Purpose

This study is designed to characterize the 

shallow aquifer structure and to estimate hydraulic 

conductivity and hydraulic gradients to quantify the 

contribution of water and DOC from a continuously 

flooded demonstration pond to an adjacent drainage 

ditch on Twitchell Island in the Sacramento-San 

Joaquin Delta. To date, research has concentrated on 

the processes and conditions that generate DOC and 

the form of DOC that has the greatest THMFP. 

Researchers have speculated on the relative 

contribution from the aerobic and anaerobic zones by 

comparing DOC concentration data from each zone 

within the peat to DOC concentrations measured in the 

drainage ditch water. However, these studies were not 

designed to estimate loading and, therefore, no attempt 

was made to quantify subsurface flow. 

This report presents hydrogeologic data 

(lithologic and geophysical logs), data to support 

calculation of a water budget and the water-budget 

calculations, and the data-collection methods for a 

cooperative study between the U.S. Geological Survey 

(USGS) and the California Department of Water 

Resources (DWR). These data were gathered to support 

the development of a two-dimensional ground-water 

flow model. The model will be used to predict the 

travel times and concentrations of DOC expected in the 

drainage ditch. 

Study Site

The study site is on Twitchell Island in the 

northwestern part of the Sacramento-San Joaquin Delta 

(fig. 1). Two 7-acre ponds, identified as East and West 

Pond, have been maintained since September 1997 

(fig. 2). East Pond is a flow-through wetland 

constructed by enclosing the area with a berm of native 

soils. Water from the nearby San Joaquin River flows 

continuously into the pond and usually tops the 

spillways. Water enters East Pond from the south using 

a gravity siphon, filling the pond to a depth of about 2 

ft. Spillways along the northern edge of the pond 

control the water depth. The spillways lead to pipes 

that convey the water away from East Pond toward the 

drainage ditch. The pond water level typically is above 

that in the ditch, creating a hydraulic gradient toward 

the ditch. A schematic cross section of pond 

construction and conceptualized flow is presented in 

figure 3.
4 Hydrogeologic Data from a Shallow Flooding Demonstration Project, Twitchell Island, California, 1997–2001

J

I H

K

L

G

irrigation pipe from

gravity siphon

west inlet east inlet

west outlet east outlet

west bridge east bridge

boardwalk

access road

N

B

pier

drainage ditch

San

Joaquin

River

SACRAMENT O

CO

CONTRA COSTA

CO

Jackson Slough

Sevenmile Slough

Threemile Slough

Twitchell Island

0

0 1 2 Kilometers

1 2 Miles

0

0 25 50 Meters

100 200 Feet

Demonstration Ponds

A

direction of surface water flow

Figure 2. Demonstration ponds location and layout. 

A, Map of Twitchell Island showing the location of the demonstration ponds relative to the network of drainage ditches. B, Diagram of east pond showing 

general layout. 
Data Collection Methods 5

The hydrogeologic characterization of the 

subsurface for this study was done at East Pond and is 

the focus of this report. West Pond is operated the same 

as East Pond, but is flooded to a depth of about 1 ft. 

East Pond is roughly rectangular in shape and is about 

200-feet wide and 1,300-feet long. It is oriented in an 

east-west direction along a drainage ditch in the central 

part of the island. To access wells installed within the 

perimeter of the pond, six piers, labeled G-L, are 

spaced apart relatively evenly around the edge and 

extend perpendicular from the berm about 20 ft into the 

pond. A boardwalk crisscrosses the pond extending 

from three locations on the north berm to two locations 

on the south berm (fig. 2B).

The general geologic framework of Twitchell 

Island and the Delta is fluvial sands, silts, and clays 

overlain by peat. Historically, the seasonal growth of 

tules, bulrush, reeds, sedge, and grasses accreted the 

Delta surface at the rate of sea level rise, 0.1 to 0.2 

centimeters per year (0.04 to 0.08 inches per year) for 

the past 8,000 years (Atwater and others, 1977). The 

slow accretion process resulted in peat beds as much as 

60-ft thick (California Department of Water Resources, 

1993). The peat beds generally are thickest near the 

Coast Range Mountains, and they thin to the east 

towards the cities of Sacramento and Stockton. 

Draining of the peat islands for agriculture began in 

1850 and essentially was complete by 1921 (Weir, 

1950).

DATA COLLECTION METHODS

Soil Coring

Prior to flooding, the peat layer was 

characterized, in part, through the collection of eight 

continuous soil cores on May 12 and 13, 1997. Cores 

were collected from the six pier locations, G–L, as well 

as from the middle of the pond at the locations labeled 

GM and JM (fig. 4). Continuous core samples were 

collected from the land surface to a depth of 9 to12 ft. 

Samples were obtained by pushing a 48-inch-long core 

barrel into the soft peat layer with a hydraulic rig. Core 

barrels were advanced to their maximum depth and 

then retrieved. Samples were extruded from the core 

barrels for measurements of recovery and for 

description. Soil-core recovery varied depending upon 

the degree of saturation and cohesion of the material. 

Saturated, noncohesive material yielded recovery rates 

of less than 10 percent, while more cohesive material 

yielded up to 100-percent recovery. Soil descriptions 

included lithology, color, layering, degree of saturation, 

and degree of visible fibrous material that persisted 

through handling.

Seepag

Fibrous Peat

Oxidized Peat

Mineral Sediment

?

?

?

?

?

?

?

?

Inlet

Outlet

Drainage Ditch

Figure 3. Conceptualized flow from the demonstration pond to drainage ditch on Twitchell Island.
6 Hydrogeologic Data from a Shallow Flooding Demonstration Project, Twitchell Island, California, 1997–2001

Borehole-Geophysical Data

Wells were logged at locations H, I, J, and K 

with an electromagnetic (EM) induction tool and a 

natural-gamma tool. The EM-induction tool measures 

the electrical conductivity of the materials surrounding 

the borehole. Total dissolved solids (TDS) 

concentration in ground water and the presence of silt 

and clay affect the electrical conductivity of sediments 

measured by an induction logger. A high response is 

interpreted in this report as an indication of relatively 

more silt and clay in the formation.

Natural gamma logs record the amount of 

gamma radiation emitted by geologic materials. The 

gamma-emitting radioisotopes that occur naturally in 

geologic materials are potassium-40 and products of 

the uranium and thorium decay series. Generally, clayrich sediments emit relatively higher gamma radiation 

than do other sediments because of the relative 

abundance of potassium (decomposition of potassium 

feldspars) or uranium and thorium (adsorption and ion 

exchange) in fine-grained materials (Keys, 1990).

Monitoring Wells

East Pond was outfitted with a network of 22 

monitoring wells (fig. 5) to monitor water quality, 

water levels, and water temperature. Monitoring 

stations were installed at four pier locations, H–K. 

Wells at each location were identified with a three- or 

four-letter well identification beginning with the station 

designation. The second letter designates the relative 

depth being monitored by the well. Shallow wells (S) 

were screened at 0.5–2 ft below land surface. Deep 

wells (D) were screened at 8–10 ft below land surface. 

Several wells (O) were screened at 23–27 ft below land 

surface. The deepest wells (HMOW and HDOW) were 

screened at 52–55 ft below land surface and 80–83 ft 

below land surface, respectively. In addition, a group of 

four drive-point wells were located between the pond 

and the drainage ditch, adjacent to station H (fig. 5). 

These drive-point wells were designated as DPH1–4. 

Table 1 (at back of report) details well-construction 

information for each of the wells in this study. The 

rotary method indicates that the wells were drilled 

using hydraulic rotary methods with bentonite mud as 

the drilling fluid. The 10-foot-deep wells were drilled 

using water as the drilling fluid. Wells HMOW and 

HDOW were sealed from the land surface down to the 

top of the sand pack with cement grout. The remaining 

wells were sealed with bentonite chips.

Figure 4. Twitchell Island demonstration pond boring locations.

J

I

H

K

L

G

GM JM

GM

irrigation pipe from gravity siphon

west inlet east inlet

west outlet east outlet

west bridge east bridge

boardwalk

access road

N

Boring location

EXPLANATION

drainage ditch

0

0 25 50 Meters

100 200 Feet

pier
Data Collection Methods 7

Water levels were measured monthly at 23 

locations. The monitoring included water levels in the 

drainage ditch and in the monitoring wells (HSP, ISP, 

JSP, KSP, DPH1, DPH2, DPH3, DPH4, DPH5, DPH6, 

DPI1, DPI2, HDP, IDP, JDP, KDP, HOW, IOW, JOW, 

KOW, HMOW, and HDOW). Depth-to-water in 

monitoring wells was measured manually with a steel 

tape that was graduated in 0.01-foot increments. 

Measurements were made by coating several feet of the 

lower end of the tape with blue chalk. The tape then 

was lowered into the well until the chalked tape 

intersected the water, creating a wetted chalk line. The 

upper part of the tape was held at an exact 1-foot mark 

against the measuring point at the top of the well 

casing. The tape then was withdrawn until the wetted 

chalk line is visible. The difference between the wetted 

chalk line and the point held at the top of the casing 

represented the depth to water below the measuring 

point. Depth-to-water measurements were converted to 

elevations by subtracting them from the surveyed 

casing elevation at each well. A 5-foot interval of 

casing was added periodically because of seasonal 

changes in water levels. The water level in the ditch 

was read directly from a staff gage on west bridge. 

Water levels in the pond were measured continuously 

with a pressure transducer and recorded on a data 

logger as hourly mean values.

Temperature Monitoring

Ground-water and surface-water temperature 

was monitored at 14 combined locations as an indicator 

of ground-water movement. Ground-water temperature 

was monitored at 12 locations and surface-water 

temperature was monitored at two locations. Suzuki 

(1960), Stallman (1963), Sorey (1971), Lapham 

(1989), Taniguchi (1993), and Constantz and others 

(1994) used temperature as an indicator of aquifer 

characteristics or dynamics. Ground-water temperature 

was monitored at 12 locations along the cross section 

(J-H) to be modeled with numerical simulations. Wells 

JSP, JDP, JOW, HSP, HDP, HOW, HMOW, HDOW 

were equipped with temperature-logging devices called 

Tidbits. Tidbits also were placed in the pond and ditch 

to monitor surface-water temperature.

Tidbits are integrated thermistor, data logger, and 

power-supply units. The manufacturer reports a 

minimum accuracy of ±0.3°C. The units are 

programmed by the user to record temperature at 

regular intervals. Date, time, and temperature were 

recorded every 30 minutes in peat-layer wells HSP, 

HDP, JSP, and JDP and every 60 minutes in the 

remaining locations. Wells DPH1–4 were fitted with 

thermistors connected to an external data logger that 

recorded every 60 minutes. These data were stored in 

the USGS National Water Information System (NWIS) 

database. 

Figure 5. Twitchell Island demonstration pond well locations. 

DPH1

irrigation pipe from gravity siphon

west inlet east inlet

west outlet east outlet

west bridge east bridge

boardwalk

access road

N

DPH2

DPH3

DPH4

ditch temperature monitoring station

HSP HDP

HOW HDOW

HMOW

JSP

JDP

JOW

DPH5

DPH6

ditch stage monitoring station

pond stage monitoring station

KSP

KSP

ISP

KOW KDP

IDP

IOW

0

0 25 50 Meters

100 200 Feet Boring location

EXPLANATION
8 Hydrogeologic Data from a Shallow Flooding Demonstration Project, Twitchell Island, California, 1997–2001

Slug Tests

Ten aquifer-slug tests were used to estimate the 

hydraulic conductivity and transmissivity of the peat 

layer and the mineral sediments beneath the peat. Four 

tests were done in the peat layer in wells HDP, IDP, 

JDP, and KDP, which were screened from 8 to 10 ft 

below land surface. Four tests were done in the finesand layer in wells HOW, IOW, JOW, and KOW, which 

were screened between 23 and 27 ft below land 

surface. One test was done in the silt layer in well 

HMOW, which was screened from 52 to 55 ft below 

land surface. One test was done in the fine silty sand 

layer in well HDOW, which was screened from 80 to 

83 ft below land surface.

Before the slug tests began, the transducer and 

data logger were calibrated over the full range of water 

levels expected during the test. The instruments were 

calibrated by comparing the depth to water, as recorded 

with the transducer and data logger, to the depth-towater measured using1-foot increments along the 

transducer cable. The calibration procedure was done 

at two wells; one with up to 7 ft of water above the 

transducer and one with up to 25 ft of water. 

Correlation coefficients between the measured depth 

below the above the transducer and the known depths 

indicate that the transducer accurately measured water 

depth (r2= 0.996 and 0.999). 

Flow Monitoring

Water was supplied to the pond at two metered 

locations referred to as the eastern and western inlets 

(fig. 5). The inlets had 4-inch-diameter polyvinyl 

chloride (PVC) pipes, fitted with ball valves to control 

flow and McCrometer propeller-type flow meters. The 

McCrometer flow meters were rated by the 

manufacturer to have ±2 percent accuracy over their 

entire rated flow range. The meters installed on the 

pond inlets at Twitchell Island were rated for flows 

between 50 and 600 gallons per minute (gal/min). Flow 

rates measured during this study ranged from 48 to 230 

gal/min. The flow rates measured were within the flow 

range of the meters for 97 percent of days measured. 

The flow meters produced eight electrical pulses per 

gallon of water that passed through the meter. The total 

count of pulses was recorded by the data logger, which 

wrote mean hourly flow rates to the memory. The 

hourly flow rates were downloaded periodically and 

averaged into daily mean values.

The only other supply of water to the pond was 

direct precipitation and possibly subsurface inflow. The 

DWR maintained a weather station on Twitchell Island 

that records hourly precipitation totals with a tippingbucket rain gage. Records from the weather station 

were obtained for the study period through the 

California Irrigation Management Information System 

(CIMIS) automated data system. The rain gage used on 

Twitchell Island had a reported accuracy of ±1 percent 

at 5 centimeters per hour (2 inches per hour) or less 

(California Irrigation Management Information 

System, accessed March 1, 2002). Precipitation was 

converted to a volumetric inflow to the pond by 

multiplying by the pond area. Inflow from beneath the 

pond was calculated as discussed in the section on 

seepage estimates.

Surface discharge from the pond was gaged at 

two locations referred to as east and west outlets 

(fig. 5). Water exited the pond through two separate 

spillways on the north side, which led to separate 24-

inch-diameter corrugated PVC pipes. The pipes passed 

through the pond berm opening toward the ditch. The 

downstream end of each conduit was fitted with a 3-

inch Parshall flume. The flumes were rated for a 

discharge range of 0.027 cubic feet per second (ft3/s) to 

1.13 ft3/s. Measured discharge was below the flumes’ 

rated capacity about 14 percent of the time. The lowdischarge measurements indicated a period when no 

water exited the pond. Stage measurements in the 

flumes were made with a pressure transducer. Druck 

PDCR1830-8388 pressure transducers used in this 

study were rated for a pressure range of 0–5 pounds per 

square inch (lbs/in2). All measurements recorded 

during the study were within the rated pressure range 

for the transducers. Hourly stage measurements for the 

pond were recorded on a data logger for periodic 

retrieval. Ditch stage was read from a staff gage and 

then subtracted from the surveyed elevation. Ditchstage measurements after October 2000 were measured 

with a pressure transducer.
Results 9

Pond loss to evaporation and uptake by plants 

was computed as evapotranspiration (ET). ET for the 

plant under consideration was calculated by 

multiplying a reference value, ETo, by the crop 

coefficient, Kc. Reference evaporation recorded hourly 

at the DWR weather station on Twitchell Island was 

multiplied by a published crop coefficient (University 

of California Cooperative Extension, 1994) to obtain 

the ET demand. Hourly ETo values were summed to 

get daily totals then multiplied by the appropriate Kc 

value to get the daily total ET demand. The Kc values 

for rice grown in the San Joaquin Valley (University of 

California Cooperative Extension, 1994) were used to 

represent East Pond. The ETo varies daily with weather 

conditions, and the crop coefficient varies with growth 

stage of the crop. The coefficient of 0.95 was used from 

planting to 10 percent ground shading (about 25 days 

beginning on April 1). The coefficient of 1.25 was used 

for plant growth between 10 percent and 75 percent 

ground shading (about 32 days). Then from 75 percent 

ground shading to harvest (about 90 days) the 

coefficient of 0.95 was used. Under cultivation, 

transpiration demand would stop after harvest, 

however, the plants in East Pond were not harvested 

and remained standing through their natural maturity. 

Therefore, a coefficient of 1.00 was used for the days 

outside the growing season. Open-water Kc is 

estimated to be a constant value of 1.10 statewide 

(University of California Cooperative Extension, 

1994). A slightly lower value was used to account for 

the continued shading of the water by standing plant 

material after the growing season ended. 

Approximately 68 percent of the pond was covered 

with standing vegetation and much of the remainder 

contained water-surface vegetation. Similar to 

precipitation, the ET estimate was converted to a 

volumetric outflow from the pond by multiplying by 

the pond area. 

The pond storage was calculated by multiplying 

water depth by pond area to obtain the volume of water 

in the pond. The surface area of the pond was assumed 

to be constant at 260,487 square feet (ft2). Hourly stage 

measurements were recorded in a data logger as 

measured by a pressure transducer. Once again, the 

transducer was rated to measure within a pressure 

range of 0–5 lbs/in2, and all measurements fell within 

the range. All transducers used during this study were 

vented to eliminate the need for barometric corrections. 

The transducer measuring pond stage was installed in a 

standpipe on the northern side of the pond (fig. 5). 

Increasing biomass in the pond was not accounted for 

in the calculation of pond storage because data were 

not sufficient to estimate a value. Not considering 

biomass in water balance calculations may have 

resulted in an overestimation of pond storage.

RESULTS

Lithologic Characterization

Soil corings and borehole geophysical data were 

used to prepare a generalized lithologic cross section of 

the pond (fig. 6). In general, the peat was a brownish, 

red-brown-to-black layer composed of mostly organic 

matter. The top 2 to 3 ft were unsaturated and 

occasionally showed soil structures (peds). Under 

cultivation, the water-table elevation on the island 

varied through the year; however, the appearance of a 

more fibrous peat at an average depth of 5 ft below land 

surface suggested that the water table did not retreat 

below that level. A more fibrous texture is interpreted 

here to mean relatively less weathering that may result 

from perennial saturation. The flooding of the test 

pond, of course, saturated the peat to the land surface.

One-eighth to one-half-inch-thick gray clay 

lenses were common throughout the peat but did not 

appear to collectively make up a significant part of the 

aquifer material. A gray muck layer was present from 2 

to 5 ft below land surface at location J and from 4.8 to 

5.2 ft below land surface at location JM. No soil cores 

could be recovered in the muck layer.

Observations made during the installation of 

monitoring wells and interpretation of borehole gamma 

and EM-induction logs were used to describe 

lithologies below the peat layer. At 15 ft below land 

surface, the organic peat is underlain by sand and clay 

in well H. A relatively continuous clay layer (about 

5-feet thick) began at 15 ft below land surface in all 

four boreholes. Alternating layers of fine sand and silt 

occurred at 20 to 64 ft below land surface. Layer 

thickness ranged from 4 to 8 ft for silts and from 8 to 

16 ft for the fine sands. A silty-clay layer existed from 

64 to 79 ft below land surface and was interrupted by a 

2-foot-thick sand layer from 74 to 76 ft below land 

surface. The hole bottomed in sand at 84 ft below land 

surface.
10 Hydrogeologic Data from a Shallow Flooding Demonstration Project, Twitchell Island, California, 1997–2001

mS/m c/s mS/m c/s c/s c/s

0 150 0

5

10

15

20

25

30

DEPTH, IN FEET BELOW LAND SURFACE

0 100

10

15

20

25

30

0 150 0

90

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

0 150 0

90

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

0 150 0

5

0

5

mS/m

0 100

10

15

20

25

30

0

5

10

15

20

25

30

0 150 0

5

10

15

20

25

30

Peat oxidized

Medium-to-fine grained sand

Clay

Peat, moderately fibrous

Peat, fibrous

No recovery

K H J I

EXPLANATION

(See fig. 4 for borehole locations)

100 200 0

5

10

15

20

25

30

mS/m

Figure 6. Geologic section and geophysical logs for selected wells on Twitchell Island, California. 

Trace to the left of the graphic logs is gamma (in counts per second) and trace to the right is electrical conductivity (in millisiemens per meter). Station 

numbers are shown at the top of the graphic log. See figure 4 for borehole locations
Results 11

Water Levels

Water-level elevations at the study site, relative 

to the NAVD 88, ranged from about –21 ft in the 

drainage ditch to about –17.5 ft in the peat layer and 

about –14 ft at about 80 ft below land surface. 

Horizontal hydraulic gradients in the peat consistently 

were toward the drainage ditch and averaged about 

0.03. Vertical hydraulic gradients from the mineral 

sediments to the peat were about 0.06 and consistently 

were oriented upward. The vertical gradients are 

evident when viewed on graphs of water elevations by 

screened interval (figs. 7A and 8). The degree of 

connection between the San Joaquin River and the 

shallow ground-water flow system can be assessed by 

qualitative comparison between ground-water levels 

(figs. 7A, 8A, and 8B) and San Joaquin River stage 

(figs. 7B). Statistical comparisons indicated that wells 

screened in the mineral sediments beneath the peat 

were best correlated with river stage measurements 

during this period. Water-level elevations measured at 

the site between September 1997 and May 2001 are 

presented in table 2 (at back of report). The USGS 

surveyed the vertical and horizontal locations of the 

measuring points with an accuracy of 0.01 foot.

Water Temperatures

Thermistors were installed during May 2000 in 

the pond, the drainage ditch, and wells DPH1–4. By the 

end of June 2000, Tidbits (temperature-logging 

devices) were installed in the remaining locations 

selected for monitoring. Average daily temperature for 

each location monitored is shown in figure 9. A few 

gaps are present in the temperature data due to 

equipment malfunction. Monitoring was discontinued 

in wells HDOW and HMOW in March 2001 because 

there was no response to land-surface temperature 

changes. 

Temperature changes propagated through the 

system in the remaining wells. The surface-water 

temperature at the pond (fig. 9B) varied from a low of 

4.7°C on January 5 and 6, 2001, to a high of 23.1°C on 

June 15, 2000. Water temperature reached a maximum 

during summer (June and July) then cooled through the 

fall and into winter. Beginning in late January 2001, the 

temperature began to rise steadily through the end of 

the record presented in this report. The same pattern of 

temperature change was observed in wells screened in 

the peat layer, except the magnitude of the change was 

reduced with increasing depth and the timing was 

shifted to later in the year. Maximum and minimum 

water temperatures were present about 30–45 days later 

than surface-water temperatures in wells screened at 

depths of 10–11 ft below land surface (fig. 9A). 

Essentially no temperature change was observed in 

wells screened below 25 ft (fig. 9B).

Estimates of Hydraulic Conductivity

Water-level recovery data from the slug tests 

were analyzed using two different analytical solutions 

(Papadopulos and others, 1973; Bouwer and Rice, 

1976) to obtain estimates of average hydraulic 

conductivity and transmissivity for each layer tested. 

Estimates of hydraulic conductivity in the peat varied 

about two orders of magnitude, from 0.01 foot per day 

(ft/d) to 0.7 ft/d (table 3, at back of report). The highest 

estimates, 9 ft/d and 5 ft/d, were obtained in the sand 

material at about 25 ft below land surface. Most of the 

estimates for sand and silt varied within one order of 

magnitude, between 1 ft/d and 9 ft/d. Hydraulic 

conductivities were estimated from slug test 

transmissivity values using a saturated thickness of 15 

ft in the peat layer, 28 ft in the sand, 56 ft in the silt, and 

85 ft in the fine silty sand. Slug test analyses are 

archived and available for viewing at the USGS District 

Office in Sacramento, California.
12 Hydrogeologic Data from a Shallow Flooding Demonstration Project, Twitchell Island, California, 1997–2001

O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O

1997 1998 1999 2000

10

16

12

14

RIVER STAGE + 10, IN FEET

ABOVE NAVD 88

EXPLANATION

Ditch

HSP (0.5-2)

ISP (0.5-2)

JSP (0.5-2)

KSP (0.5-2)

DPH2 (2-2.5)

DPH4 (2-2.5)

DPI2 (2-2.5)

DPH6(4.9-5.4)

–23

–22

–21

–20

–19

–18

–17

–16

–15

WATER LEVEL ELEVATION,

IN FEET ABOVE NAVD 88

O N D J F MA MJ JA S O N D J F MAMJ J A S O N D J FM AMJ J A

1997 1998 1999 2000

N D J F MA

2001

DATE

A

B

S O

N

Figure 7. Water level response in shallow wells in relation to the San Joaquin River stage at Twitchell Island, California. 

A, Water levels in shallow wells and drive points in upper peat layer. Numbers in parentheses are depth of screened interval, in feet. B, San Joaquin River 

stage at Jersey Point. San Joaquin river stage is tidally corrected using a Godin filter; gaps in curve indicate missing data; NAVD 88, North American Vertical 

Datum of 1988.
Results 13

O N D J F MA MJ JA S O N D J F MAMJ J A S O N D J F MAMJ J A N DJ FMA

–20

–19

–18

–17

–16

–15

–14

–13

–12

WATER LEVEL ELEVATION, IN FEET ABOVE NAVD 88

O N D J F MA MJ JA S O N D J F MAMJ J A SO N DJ F MAMJ J A

1997 1998 1999 2000

N DJ FMA

2001

A

B

DPH1 (10-11)

DPH3 (10-11)

DPI1 (10-11)

DPH5 (10.74-11.74)

HDP (8-10)

IDP (8-10)

JDP (8-10)

KDP (8-10)

IOW (23-25)

HOW (25-27)

JOW (25-27)

KOW (25-27)

HMOW (52-55)

HDOW (80-83)

DATE

S O

S O

–15

–16

–17

–18

–19

–20

–21

–22

–23

Figure 8. Water level in wells at Twitchell Island, California. 

A, Water levels in wells and drive points screened in lower peat layer. B, Water levels in wells screened in mineral sediments. Numbers in parentheses are 

depth of screened interval, in feet; NAVD 88, North American Vertical Datum of 1988.
14 Hydrogeologic Data from a Shallow Flooding Demonstration Project, Twitchell Island, California, 1997–2001

0

5

10

15

20

25

POND

HDP (8-10)

JDP (8-10)

DPH1 (10-11)

DPH2 (2-2. 5)

DPH3 (10- 11)

DPH4 (2-2 .5)

0

5

10

15

20

25

DATE

WATER TEMPERATURE, IN DEGREES CELSIUS

2000 2001

A

B

POND

HOW (25-27)

JOW (25-27)

HMOW (52-55)

HDOW (80-83)

DITCH

D J F M A M J

M J J A S O N D J F M A M J

M J J A S O N D

Figure 9. Water temperature in wells on Twitchell Island, California. 

A, Water temperature in wells screened in peat layers and pond, May 2000 to June 2001. B, Water temperature in wells screened in mineral sediments and 

in pond and ditch. Numbers in parentheses are depth of screened interval, in feet. 
Results 15

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

1

1

DAILY MEAN INFLOW TO POND, IN CUBIC FEET PER SECOND

PRECIPITATION

EAST INLET

WEST INLET

O

DATE

2000 2001

0. 00

0. 10

0. 20

0. 30

0. 40

0. 50

0. 60

0. 70

0. 80

0. 90

1. 00

EVAPOTRANSPIRATION

WEST OUTLET

EAST OUTLET

N D J F M A M J J A S

O N D J F M A M J J A S

A

B

Figure 10. Water budget for East Pond from October 2000 through September 2001 on Twitchell Island, California. 

A, Surface water inflow to East Pond. Surfaces are stacked to depict the contribution of each component. B, Surface water outflow from East Pond. C, Daily 

mean change in storage in East Pond. 
16 Hydrogeologic Data from a Shallow Flooding Demonstration Project, Twitchell Island, California, 1997–2001

Seepage Estimates

Under continuously flooded conditions, seepage 

from the flooded area is the primary source of water 

flowing through the peat and, thus, is the main carrier 

of DOC to the ditch. Therefore, to estimate DOC 

loading to the drainage ditch, subsurface discharge 

from the pond must be determined. Although the 

seepage from the pond cannot be directly measured, the 

components of the pond water budget, such as pond 

inflow and outflow and pond storage were directly 

measured, and can be used to estimate the net seepage 

from the pond. Daily mean flow rates are summarized 

in tables 4 and 5 (at back of report) for eastern and 

western inlets, respectively. Daily mean discharge for 

east and west outlets are summarized in tables 6 and 7 

(at back of report), respectively. The seepage rate is 

calculated as the difference between the total of 

quantifiable flows to and from the system and the 

change in pond storage (table 8 (at back of report); 

fig. 10). Zero pond inflow reflects intervals when no 

water was siphoned from the San Joaquin River. 

Although some of the flow parameters have been 

monitored since 1997, only measurements beginning in 

October 2000 were used in the water budget. Before 

October 2000, a significant amount of water escaped 

the pond through a crack beneath the perimeter berm. 

Repairs to the system were complete in late summer 

2000. A bentonite slurry wall was installed to stop the 

flow beneath the berm and to force the water to exit the 

pond through the flumes. 

Seepage estimates from the water budget ranged 

from 0.96 ft3/s to -0.21 ft3/s (table 8, at back of report). 

Positive values indicate seepage from the pond. The 

estimated average seepage during the 1-year period 

was 0.18 ft3/s. When data are excluded because, for 

various reasons, daily mean values did not include 24 

hourly measurements or measured flow was outside the 

instrument range the estimated average seepage was 

0.26 ft3/s.

SUMMARY

This report presents the methods used, and data 

collected, during the U. S. Geological Survey and 

California Department of Water Resources study to 

determine the effects of continuous shallow flooding 

O

DATE

2000 2001

N D J F M A M J J A S

–0.60

–0.40

–0.20

0.00

0.20

0.40

0.60

0.80

DAILY MEAN CHANGE, IN POND STORAGE

IN CUBIC FEET PER SECOND

Figure 10.—Continued.
References Cited 17

on ground-water discharge to an agricultural drainage 

ditch on Twitchell Island. The conceptual model was 

detailed with soil coring and borehole geophysical 

logs. Twenty-two monitoring wells were installed to 

observe hydraulic head. Ground-water and surfacewater temperatures were monitored at 14 locations. 

Flow to and from the pond was monitored through 

direct measurement of flows and through the 

calculation of a water budget. Aquifer slug tests were 

done in peat and mineral sediments to estimate 

hydraulic conductivity.

These data were gathered to support the 

development of a two-dimensional ground-water flow 

model. The model will be used to estimate subsurface 

discharge to the drainage ditch, and to estimate the 

concentrations of dissolved organic carbon that can be 

expected in the ditch. 

REFERENCES CITED

Atwater, B.F., Hedel, C.W., and Helley, E.J., 1977, Late 

Quaternary depositional history, Holocene sea-level 

changes, and vertical crustal movement, southern San 

Francisco Bay, California: U.S. Geological Survey 

Professional Paper 1014, 15 p.

Bouwer, H. and Rice, R.C., 1976, A slug test for determining 

hydraulic conductivity of unconfined aquifers with 

completely or partially penetrating wells: Water 

Resources Research, v. 12, no. 3, p. 423-428.

California Department of Water Resources, 1993, 

Sacramento-San Joaquin Delta atlas: California 

Department of Water Resources, 121 p.

California Irrigation Management Information System: 

accessed March 1, 2002, at URL 

http://www.cimis.water.ca.gov/.

Constantz, J., Thomas, C.L., and Zellweger, G., 1994, 

Influence of diurnal variation in stream temperature on 

streamflow loss and ground water recharge, Water 

Resources Research, v. 30, no. 12, p. 3253-3264.

Deverel, S.J., and Rojstaczer, S., 1996, Subsidence of 

agricultural land in the Sacramento-San Joaquin Delta, 

California: Role of aqueous and gaseous carbon fluxes, 

Water Resources Research, v. 32, no. 8, p. 2359-2367.

Deverel, S.J., Wang, B., and Rojstaczer, S., 1998, 

Subsidence of organic soils, Sacramento-San Joaquin 

Delta, California, in Borchers, J.W. (ed) Land 

Subsidence Histories and Current Research: 

Proceedings of the Dr. Joseph F. Poland Symposium, 

Association of Engineering Geologists Special 

Publication No. 8: Belmont, Star Publishing Co.

Fujii, R., Ranalli, A.J., Aiken, G.R., and Bergamaschi, B.A., 

1998, Dissolved organic carbon concentrations and 

compositions, and trihalomethane formation potentials 

in water from agricultural peat soils, Sacramento-San 

Joaquin Delta, California: Implications for drinking 

water quality, U.S. Geological Survey Water Resources 

Investigation Report 98-4147, 22 p.

Keys, W.S., 1990, Borehole geophysics applied to groundwater investigations: U.S. Geological Survey 

Techniques of Water-Resources Investigations, book 2, 

chap. E2, 150 p.

Lapham, W.W., 1989, Use of temperature profiles beneath 

streams to determine rates of vertical ground-water flow 

and vertical hydraulic conductivity, United States 

Geological Survey Water-Supply Paper 2337, 35 p.

Miller, R.L., Hastings, L., and Fujii, R., 2000, Hydrologic 

treatments affect gaseous carbon loss from organic 

soils, Twitchell Island, California: U.S. Geological 

Survey Water-Resources Investigation Report 00-4042, 

21 p.

Papadopulos, S.S., Bredehoeft, J.D., and Cooper, H.H., Jr., 

1973, On the analysis of slug test data, Water Resources 

Research, v. 9, no. 4, p. 1087-1089.

Rojstaczer, S.A., Hamon, R.E., Deverel, S.J., and Massey, 

C.A., 1991, Evaluation of selected data to assess the 

causes of subsidence in the Sacramento-San Joaquin 

Delta, California: U.S. Geological Survey Open-File 

Report 91-193, 16 p.

Sorey, M.L., 1971, Measurement of vertical ground water 

velocity from temperature profiles in water wells, Water 

Resources Research, v. 7, no. 4, p. 963-970.

Stallman, R.W., 1963, Computation of ground water velocity 

from temperature data, United States Geological Survey 

Water-Supply Paper 1544-H, 10 p.

Suzuki, S., 1960, Percolation measurements based on heat 

flow through soil with special reference to paddy fields, 

Journal of Geophysical Research, v. 65, no. 9, p. 2883-

2885.

Taniguchi, M., 1993, Evaluation of vertical ground water 

fluxes and thermal properties of aquifers based on 

transient temperature – depth profiles, Water Resources 

Research, v. 29, n. 7, p. 2021-2026.

University of California Cooperative Extension, 1994, Using 

reference evapotranspiration (eto) and crop coefficients 

to estimate crop evapotranspiration (etc) for agronomic 

crops, grasses, and vegetable crops: Leaflet 21427, 

12 p.

U.S. Environmental Protection Agency, 2002, National 

primary drinking water standards: U.S. Environmental 

Protection Agency publication EPA 816-F-02-013, July 

2002, 7 p.

Weir, W.W., 1950, Subsidence of peat lands of the 

Sacramento-San Joaquin Delta, California: Hilgardia, 

v. 20, 20 p.
18 Hydrogeologic Data from a Shallow Flooding Demonstration Project, Twitchell Island, California, 1997–2001 Well name State well number USGS site number Elevation of top of casing Drilling method Well depth Screened interval Sand pack interval Grout interval 

(feet below land surface) 

HSP 003N003E16G005M 380626121383505 -14.89 auger 2 0.5–2 0.5–2 0–0.5 HDP 003N003E16G004M 380626121383504 -14.83 rotary 10 8–10 8–10 0–8 HOW1

1Casing elevation was -11.26 after 2/26/98.

003N003E16G003M 380626121383503 -16.26 rotary 27 25–27 23–27 0–23 

HMOW2

2Casing elevation was -14.21 from 3/6/98 to 3/28/98, -19.21 from 2/26/98 to 3/5/98, and -19.21 after 3/28/98.

003N003E16G002M 380626121383502 -21.73 rotary 60 52–55 50–57 0–50 

HDOW3

3Casing elevation was -8.96 after 1/28/98. 

003N003E16G001M 380626121383501 -13.96 rotary 88 80–83 78-85 0–78 

DPH1 003N003E16G006M 380627121383601 -15.28 driven 11 10–11 N/A N/A DPH2 003N003E16G007M 380627121383602 -17.32 driven 2.5 2–2.5 N/A N/A DPH3 003N003E16G008M 380626121383506 -14.59 driven 11 10–11 N/A N/A DPH4 003N003E16G009M 380626121383507 -16.67 driven 2.5 2–2.5 N/A N/A DPH54

4Casing elevation was -17.71 from 1/6/98 to 1/25/99, -18.81 from 12/18/97 to 1/5/98, and -15.66 after 1/28/99.

003N003E16B001M 380627121383603 -14.05 driven 11.74 10.74–11.74 N/A N/A 

DPH65

5Casing elevation was -15.99 after 2/26/98. 

003N003E16B002M 380627121383604 -18.10 driven 5.4 4.9–5.4 N/A N/A 

ISP 003N003E16G012M 380626121383203 -14.45 auger 2 0.5–2 0.5–2 0–0.5 IDP 003N003E16G011M 380626121383202 -14.95 rotary 10 8–10 8–10 0–8 IOW6

6Casing elevation was -11.14 after 2/26/98. 

003N003E16G010M 380626121383201 -16.14 rotary 25 23–25 21–25 0–21 

DPI1 003N003E16G013M 380627121383201 -14.89 driven 11 10–11 N/A N/A DPI2 003N003E16G014M 380627121383202 -17.11 driven 2.5 2–2.5 N/A N/A JSP 003N003E16G017M 380624121383303 -14.78 auger 2 0.5–2 0.5–2 0–0.5 JDP 003N003E16G016M 380624121383302 -15.09 rotary 10 8–10 8–10 0–8 JOW7

7Casing elevation was -11.32 after 2/26/98.

003N003E16G015M 380624121383301 -16.32 rotary 27 25–27 23–27 0–23 

KSP 003N003E16G020M 380624121384003 -14.95 auger 2 0.5–2 0.5–2 0–0.5 KDP 003N003E16G019M 380624121384002 -15.25 rotary 10 8–10 8–10 0–8 KOW8

8Casing elevation was -11.80 after 1/28/98.

003N003E16G018M 380624121384001 -16.80 rotary 27 25–27 23–27 0–23 

Table 1. Well construction details for wells on Twitchell Island, California[N/A, not applicable. Elevations are in feet, relative to the North American Vertical Datum of 1988]
Table 2 19

Upper 5 and one-half feet of peat

Date Ditch HSP

(0.5–2.0)

ISP 

(0.5–2.0)

JSP

(0.5–2.0) 

KSP 

(0.5–2.0)

DPH2

(2–2.5)

DPH4

(2–2.5)

DPI2

(2–2.5)

DPH6 

(4.9–5.4)

09/11/97 -- dry dry dry dry -21.49 -21.93 -21.57 --

10/07/97 -- -17.80 -17.78 -17.67 -17.69 -- -- -- --

10/10/97 -- -17.75 -17.74 -17.65 -17.65 -22.17 -19.66 -- --

10/15/97 -- -17.63 -17.64 -17.57 -17.56 -21.19 -19.65 -21.17 --

10/28/97 -- -17.81 -17.86 -17.69 -17.67 -- -- -- --

10/29/97 -- -- -17.79 -- -- -- -- -21.47 --

10/30/97 -- -17.58 -- -- -- -21.29 -19.66 -21.45 --

11/14/97 -- -- -- -17.65 -17.63 -- -- -- --

11/17/97 -- -17.79 -17.87 -- -- -- -- -- --

11/21/97 -22.18 -17.71 -17.68 -17.62 -17.65 -21.31 -19.67 -21.25 -25.12

12/02/97 -21.96 -17.73 -17.70 -17.68 -17.68 -21.28 -19.66 -21.30 -21.85

12/09/97 -21.66 -17.81 -17.77 -17.65 -17.65 -21.11 -19.67 -21.06 -21.36

12/18/97 -21.52 -17.99 -17.86 -17.88 -17.82 -20.78 -19.66 -20.71 -20.81

01/06/98 -22.07 -18.69 -18.58 -18.53 -18.54 -21.42 -19.70 -21.24 -20.71

01/20/98 -- -17.90 -17.84 -17.74 -17.79 -19.04 -18.70 -18.74 --

01/28/98 -21.18 -18.27 -18.18 -18.06 -18.09 -20.83 -19.64 -20.43 -19.91

02/25/98 -- -16.92 -16.84 -16.86 -16.91 -- -- -- --

02/26/98 -19.35 -- -- -- -- -- -16.98 -- --

03/10/98 -- -18.25 -18.21 -18.18 -18.22 -- -- -- -18.43

03/11/98 -- -- -- -- -- -18.49 -19.61 -18.87 --

03/19/98 -- -18.68 -18.52 -18.50 -18.53 -20.84 -19.67 -21.24 -19.32

03/26/98 -- -17.99 -17.76 -17.77 -17.79 -21.21 -19.64 -21.49 -19.72

04/02/98 -19.87 -17.93 -17.78 -17.73 -17.75 -20.42 -19.58 -19.81 -22.05

04/15/98 -21.79 -17.88 -17.78 -17.76 -17.78 -21.25 -19.64 -21.50 -20.60

04/16/98 -21.50 -17.68 -17.58 -- -- -21.25 -19.62 -22.12 -22.11

04/20/98 -21.94 -17.91 -17.77 -17.71 -17.72 -21.50 -19.63 -21.60 -21.24

04/22/98 -21.86 -17.67 -17.55 -17.49 -17.50 -21.44 -19.60 -21.59 -21.16

04/24/98 -21.71 -17.88 -17.72 -- -- -21.44 -19.62 -21.59 -21.11

05/05/98 -21.75 -17.80 -17.68 -17.58 -17.58 -21.35 -19.60 -21.48 -21.11

05/08/98 -21.70 -17.75 -17.61 -17.49 -17.50 -21.38 -19.61 -21.51 -21.09

05/12/98 -21.70 -17.76 -17.55 -17.45 -17.44 -21.32 -19.59 -21.52 -21.10

05/15/98 -21.77 -17.80 -17.57 -17.47 -17.47 -21.26 -19.57 -21.52 -21.09

05/18/98 -21.94 -17.81 -17.57 -17.48 -17.49 -21.18 -19.58 -21.51 -21.05

05/20/98 -21.92 -17.80 -17.57 -17.49 -17.51 -21.25 -19.60 -21.58 -21.05

05/22/98 -21.87 -17.77 -17.53 -17.42 -- -21.28 -19.59 -21.59 -21.06

Table 2. Ground-water elevations on Twitchell Island, California, From Setpember 1997 to September 2001

[--, no measurement was made on that date. Screened interval indicated in parentheses; *, statistical measures shown for information only; values may not be 

comparable due to missing data]
20 Hydrogeologic Data from a Shallow Flooding Demonstration Project, Twitchell Island, California, 1997–2001

Upper 5 and one-half feet of peat

Date Ditch HSP 

(0.5–2.0)

ISP 

(0.5–2.0)

JSP 

(0.5–2.0) 

KSP 

(0.5–2.0)

DPH2

(2–2.5)

DPH4

(2–2.5)

DPI2

(2–2.5)

DPH6 

(4.9–5.4)

05/26/98 -21.88 -17.77 -17.50 -17.45 -17.43 -21.33 -19.61 -21.53 -21.06

05/28/98 -21.77 -17.78 -17.51 -17.42 -17.41 -21.37 -19.62 -21.54 -21.06

06/30/98 -21.81 -17.70 -17.53 -17.32 -17.30 -21.17 -19.46 -21.69 -21.43

07/30/98 -20.95 -18.01 -18.08 -17.56 -17.47 -21.01 -19.56 -21.11 -23.88

08/31/98 -20.13 -18.22 -18.09 -17.47 -17.44 -19.89 -19.54 -19.84 -21.49

09/22/98 -21.83 -18.25 -18.14 -17.48 -17.43 -21.17 -19.57 -20.99 -21.38

10/29/98 -- -- -17.98 -17.48 -17.45 -21.19 -19.20 -21.12 -21.78

12/04/98 -21.74 -18.00 -18.00 -17.54 -17.52 -21.34 -19.55 -21.16 -20.93

01/11/99 -20.57 -17.84 -17.95 -17.24 -17.51 -20.46 -19.38 -- -20.71

01/26/99 -21.54 -17.99 -17.88 -17.50 -17.55 -20.92 -19.43 -- -20.42

02/24/99 -21.60 -17.98 -17.94 -17.58 -17.57 -21.05 -19.44 -21.02 -19.76

04/07/99 -- -18.06 -17.71 -17.59 -17.55 -21.25 -19.43 -21.21 -20.78

05/19/99 -21.52 -18.11 -17.70 -17.58 -17.57 -21.27 -19.49 -20.41 -21.40

07/16/99 -21.21 -18.27 -17.57 -17.55 -17.52 -20.88 -19.61 -20.83 -22.32

08/25/99 -21.33 -18.84 -17.75 -17.60 -17.58 -20.85 -19.62 -- --

11/16/99 -22.36 -18.19 -17.76 -17.69 -17.69 -21.07 -19.55 -20.93 --

12/28/99 -20.74 -17.96 -17.60 -17.55 -17.51 -20.03 -19.38 -20.17 --

01/22/00 -- -17.72 -17.47 -17.42 -17.46 -18.91 -18.53 -19.50 -20.71

04/24/00 -20.44 -17.77 -17.61 -17.62 -17.61 -18.12 -19.44 -19.46 -18.86

05/11/00 -21.50 -17.99 -17.80 -17.81 -17.79 -21.23 -19.42 -21.31 -20.67

06/26/00 -21.53 -17.04 -17.76 -17.75 -17.75 -21.22 -19.43 -21.26 -22.77

07/31/00 -- -17.82 -17.28 -17.30 -17.25 -20.08 -20.05 -21.00 --

09/06/00 -21.43 -18.00 -17.74 -17.53 -17.50 -20.12 -20.57 -21.17 --

10/30/00 -21.99 -17.88 -17.27 -17.27 -17.16 -21.01 -20.36 -21.00 --

12/04/00 -- -17.61 -17.20 -17.16 -17.01 -21.02 -20.26 -20.36 -22.65

01/02/01 -- -17.60 -17.39 -17.32 -17.35 -21.23 -19.37 -21.11 --

02/06/01 -22.46 -17.49 -17.37 -17.35 -17.32 -21.18 -19.35 -21.13 -20.36

03/14/01 -22.45 -17.63 -17.46 -17.37 -17.37 -21.26 -19.35 -21.20 -20.26

04/17/01 -- -17.70 -17.66 -17.42 -17.37 -21.31 -19.37 -21.18 -20.76

05/22/01 -- -17.60 -17.79 -17.42 -17.39 -21.31 -19.35 -- -21.08

06/18/01 -- -18.10 -17.81 -17.40 -17.41 -21.02 -19.42 -- -20.99

07/16/01 -- -- -- -- -- -- -- -- --

08/20/01 -- -18.13 -17.88 -17.42 -17.39 -20.97 -19.42 -- -22.12

09/20/01 -- -- -- -- -- -- -- -- --

Minimum* -22.46 -18.84 -18.58 -18.53 -18.54 -22.17 -21.93 -22.12 -25.12

Median* -21.71 -17.81 -17.74 -17.55 -17.52 -21.19 -19.59 -21.20 -21.06

Mean* -21.55 -17.90 -17.74 -17.58 -17.59 -20.92 -19.56 -21.03 -21.21

Maximum* -19.35 -16.92 -16.84 -16.86 -16.91 -18.12 -16.98 -18.74 -18.43

Table 2. Ground-water elevations on Twitchell Island, California, from September 1997 to September 2001—Continued
Table 2 21

Lower seven feet of peat

Date HDP

(8–10)

IDP

(8–10)

JDP

(8–10)

KDP

(8–10)

DPH1

(10–11)

DPH3

(10–11)

DPI1

(10–11)

DPH5 

(10.74–11.74)

09/11/97 -19.40 -19.75 -19.59 -19.64 -21.35 -21.22 -21.25 --

10/07/97 -17.58 -18.45 -17.85 -17.49 -- -- -- --

10/10/97 -17.71 -20.04 -18.03 -17.63 -21.37 -20.89 -- --

10/15/97 -17.41 -18.21 -17.57 -17.35 -21.42 -20.78 -21.37 --

10/28/97 -17.51 -17.96 -17.51 -17.46 -- -- -- --

10/29/97 -- -- -- -- -- -- -21.34 --

10/30/97 -17.34 -17.82 -- -- -21.41 -20.66 -21.02 --

11/14/97 -- -- -17.55 -17.51 -- -- -- --

11/17/97 -17.55 -17.93 -- -- -- -- -- --

11/21/97 -17.65 -18.88 -18.83 -19.45 -21.53 -20.57 -22.37 -21.10

12/02/97 -17.57 -18.44 -17.68 -18.41 -21.34 -20.54 -21.36 -20.81

12/09/97 -17.97 -18.35 -17.67 -17.65 -21.18 -20.47 -21.15 --

12/18/97 -17.87 -18.36 -17.59 -17.65 -20.68 -20.26 -20.62 -20.82

12/19/97 -- -- -- -- -- -- -- -20.65

01/06/98 -18.21 -18.52 -18.27 -18.06 -21.21 -20.54 -21.17 -19.86

01/20/98 -19.43 -18.39 -17.51 -17.56 -19.37 -19.28 -19.42 --

01/26/98 -- -- -- -- -- -- -- --

01/28/98 -17.87 -18.20 -17.75 -17.72 -20.10 -19.98 -20.00 -19.24

02/25/98 -16.67 -17.13 -16.55 -16.53 -- -- -- --

02/26/98 -- -- -- -- -16.83 -16.87 -16.80 --

03/10/98 -17.77 -17.79 -17.69 -17.74 -- -- -- -18.00

03/11/98 -- -- -- -- -18.19 -18.43 -18.04 --

03/19/98 -18.09 -18.15 -17.99 -18.11 -20.25 -20.11 -20.13 -18.96

03/26/98 -17.49 -17.73 -17.35 -17.34 -20.87 -20.45 -20.83 -18.78

04/02/98 -17.47 -17.66 -17.33 -17.32 -20.70 -20.31 -20.74 -19.18

04/15/98 -17.49 -17.68 -17.33 -17.11 -21.08 -20.52 -21.10 -19.29

04/16/98 -17.32 -17.54 -- -- -21.86 -- -- -21.01

04/20/98 -17.45 -17.62 -17.29 -17.35 -21.46 -21.49 -22.17 -19.56

04/22/98 -17.25 -17.39 -18.07 -17.15 -21.39 -21.13 -21.86 -19.52

04/24/98 -17.41 -17.58 -- -- -21.34 -20.94 -21.67 -19.53

05/05/98 -17.39 -17.50 -17.17 -17.28 -21.17 -20.58 -21.26 -19.71

05/08/98 -17.33 -17.47 -17.12 -16.92 -21.16 -20.55 -21.22 -19.74

05/12/98 -17.27 -17.37 -17.04 -17.16 -21.19 -20.58 -21.22 -19.79

05/15/98 -17.36 -17.52 -17.14 -17.24 -21.18 -20.57 -21.22 -19.82

05/18/98 -17.36 -17.51 -17.13 -17.24 -21.19 -20.56 -21.19 -19.83

05/20/98 -17.38 -17.52 -17.15 -17.27 -21.19 -20.57 -21.20 -19.82

05/22/98 -17.33 -17.48 -17.10 -17.21 -21.20 -20.58 -21.20 -19.85

05/26/98 -17.33 -17.45 -17.10 -17.23 -21.20 -20.63 -21.21 -19.89

05/28/98 -17.32 -17.44 -17.08 -17.20 -21.19 -20.63 -21.21 -19.91

06/30/98 -17.31 -17.47 -17.07 -17.20 -21.20 -20.53 -21.25 -20.07

Table 2. Ground-water elevations on Twitchell Island, California, from September 1997 to September 2001—Continued
22 Hydrogeologic Data from a Shallow Flooding Demonstration Project, Twitchell Island, California, 1997–2001

Lower seven feet of peat

Date HDP

(8–10)

IDP

(8–10)

JDP

(8–10)

KDP

(8–10)

DPH1

(10–11)

DPH3

(10–11)

DPI1

(10–11)

DPH5 

(10.74–11.74)

07/30/98 -17.55 -17.63 -17.31 -17.42 -21.18 -20.61 -21.20 -20.73

08/31/98 -17.58 -17.61 -17.28 -17.39 -19.82 -19.81 -19.77 -19.74

09/22/98 -17.66 -17.69 -17.31 -17.43 -20.95 -20.45 -20.97 -19.82

10/29/98 -17.70 -17.75 -17.37 -17.50 -21.24 -20.65 -21.27 -20.27

12/04/98 -17.23 -17.84 -17.46 -17.57 -21.34 -20.60 -21.29 -20.05

01/11/99 -17.71 -17.80 -17.40 -17.42 -20.49 -20.09 -- -19.81

01/26/99 -17.78 -17.72 -17.38 -16.90 -20.75 -20.38 -- -19.54

02/24/99 -17.68 -17.74 -17.38 -17.29 -20.52 -20.50 -- -19.41

03/10/99 -17.77 -- -- -- -- -- -- --

04/07/99 -17.66 -17.72 -17.34 -17.38 -21.30 -20.66 -21.34 -19.50

05/19/99 -17.71 -17.73 -17.29 -17.37 -21.42 -20.71 -21.37 -19.99

07/16/99 -17.77 -17.78 -17.39 -17.49 -20.64 -20.40 -20.62 -20.63

08/25/99 -17.76 -17.81 -17.47 -17.58 -20.77 -20.50 -- --

11/16/99 -17.98 -18.70 -17.77 -17.80 -21.06 -20.64 -20.53 -21.16

12/28/99 -17.84 -18.15 -17.59 -17.61 -20.49 -20.20 -20.39 -20.73

01/22/00 -17.70 -17.92 -17.35 -17.44 -19.97 -19.76 -19.95 -19.57

04/24/00 -17.50 -17.62 -17.25 -17.27 -19.91 -19.22 -19.04 --

05/11/00 -17.76 -17.87 -17.42 -17.47 -21.37 -20.76 -21.09 -19.20

06/26/00 -17.80 -17.90 -17.58 -17.55 -21.17 -20.73 -21.09 -20.53

07/31/00 -17.50 -17.57 -17.13 -17.30 -20.87 -20.18 -20.87 --

09/06/00 -17.83 -18.20 -17.46 -17.72 -21.03 -20.34 -20.94 -21.85

10/30/00 -17.69 -17.74 -17.33 -17.40 -21.00 -20.31 -20.96 --

12/04/00 -17.64 -18.05 -17.30 -17.35 -21.03 -20.34 -20.56 -20.71

01/02/01 -17.75 -17.89 -17.47 -17.50 -21.16 -20.50 -20.99 --

02/06/01 -17.65 -17.67 -17.36 -18.00 -21.15 -20.55 -21.01 -19.91

03/14/01 -17.72 -17.85 -17.42 -17.40 -21.09 -20.48 -20.99 -19.83

04/17/01 -17.73 -17.80 -17.38 -17.44 -21.18 -20.58 -20.97 -20.10

05/22/01 -17.72 -17.69 -17.39 -17.43 -20.89 -20.50 -20.99 -20.34

06/18/01 -17.72 -17.70 -17.31 -17.44 -20.60 -20.39 -- -20.38

06/26/01 -- -- -- -- -- -- -- --

07/16/01 -17.69 -17.63 -17.31 -17.44 -20.63 -20.37 -- -21.60

07/31/01 -- -- -- -- -- -- -- --

08/20/01 -17.79 -17.65 -17.49 -17.52 -20.61 -20.31 -- --

09/20/01 -17.82 -17.69 -17.43 -17.56 -20.75 -20.39 -20.72 --

Minimum* -19.43 -20.04 -19.59 -19.64 -21.86 -21.49 -22.37 -21.85

Median* -17.66 -17.74 -17.38 -17.44 -21.16 -20.52 -21.09 -19.85

Mean* -17.68 -17.92 -17.50 -17.54 -20.88 -20.40 -20.87 -20.04

Maximum* -16.67 -17.13 -16.55 -16.53 -16.83 -16.87 -16.80 -18.00

Table 2. Ground-water elevations on Twitchell Island, California, from September 1997 to September 2001—Continued
Table 2 23

Beneath peat

Date IOW

(23-25)

HOW

(25-27)

JOW

(25-27)

KOW

(25-27)

HMOW

(52-55)

HDOW

(80-83)

09/11/97 -17.69 -17.80 -17.74 -17.97 -17.77 -14.33

10/07/97 -17.66 -17.74 -17.71 -17.80 -17.70 -14.31

10/10/97 -17.66 -17.75 -17.64 -17.78 -17.71 -14.36

10/15/97 -17.63 -17.72 -17.64 -17.78 -17.67 -14.36

10/28/97 -17.68 -17.78 -17.72 -17.80 -- --

10/29/97 -- -- -- -- -- --

10/30/97 -- -17.73 -- -- -17.80 -14.43

11/14/97 -- -- -17.59 -17.83 -- --

11/17/97 -17.59 -17.65 -- -- -17.54 -14.40

11/21/97 -17.56 -17.64 -17.51 -17.77 -17.55 -14.30

12/02/97 -17.32 -17.42 -17.32 -17.48 -17.34 -14.03

12/09/97 -17.14 -17.23 -17.24 -17.32 -17.21 --

12/18/97 -17.02 -17.11 -17.10 -17.45 -17.06 --

12/19/97 -- -- -- -- -- --

01/06/98 -17.07 -17.20 -16.79 -17.30 -17.12 --

01/20/98 -- -- -- -- -- --

01/26/98 -- -- -- -- -- --

01/28/98 -16.61 -16.70 -16.61 -16.80 -- -13.09

02/25/98 -15.17 -15.27 -15.24 -15.32 -- -12.48

02/26/98 -15.19 -15.24 -15.29 -15.38 -17.33 --

03/04/98 -- -- -15.85 -15.97 -- --

03/06/98 -15.89 -15.97 -- -- -15.99 --

03/10/98 -16.17 -16.26 -16.27 -16.42 -16.29 -12.76

03/11/98 -- -16.38 -- -- -16.41 -12.83

03/19/98 -16.74 -16.88 -16.80 -17.06 -16.87 --

03/26/98 -16.72 -16.86 -16.78 -17.03 -16.85 -13.20

04/02/98 -16.57 -16.69 -16.64 -16.85 -16.68 -13.19

04/15/98 -16.90 -17.03 -16.93 -17.19 -17.02 -13.45

04/16/98 -- -- -- -- -- --

04/20/98 -17.01 -17.13 -17.02 -17.29 -17.12 -13.58

04/22/98 -16.97 -17.11 -17.00 -17.26 -17.09 -13.56

04/24/98 -17.00 -17.14 -- -- -17.12 --

05/05/98 -17.07 -17.20 -17.01 -17.36 -17.19 -13.69

05/08/98 -17.06 -17.19 -17.09 -17.36 -17.19 -13.69

05/12/98 -16.99 -17.13 -17.02 -17.30 -17.12 -13.61

05/15/98 -17.03 -17.15 -17.05 -17.35 -17.14 -13.64

05/18/98 -17.08 -17.21 -17.01 -17.36 -17.20 -13.69

05/20/98 -17.09 -17.23 -17.11 -17.38 -17.20 -13.69

05/22/98 -17.09 -17.23 -17.14 -17.39 -17.22 -13.72

05/26/98 -- -17.23 -17.12 -17.39 -17.21 -13.65

Table 2. Ground-water elevations on Twitchell Island, California, from September 1997 to September 2001—Continued
24 Hydrogeologic Data from a Shallow Flooding Demonstration Project, Twitchell Island, California, 1997–2001

Beneath peat

Date IOW

(23-25)

HOW

(25-27)

JOW

(25-27)

KOW

(25-27)

HMOW

(52-55)

HDOW

(80-83)

05/28/98 -17.10 -17.22 -17.12 -17.39 -17.22 -13.65

06/30/98 -17.13 -17.24 -17.12 -17.40 -17.22 -13.71

07/30/98 -17.28 -17.37 -17.32 -17.58 -17.39 -13.90

08/31/98 -17.24 -17.35 -17.31 -17.51 -17.33 -14.06

09/22/98 -17.57 -17.66 -17.60 -17.82 -17.67 -14.27

10/28/98 -- -- -- -- -17.69 -14.38

10/29/98 -17.61 -17.72 -17.62 -17.84 -17.71 -14.38

12/04/98 -17.50 -17.61 -17.40 -17.64 -17.53 -14.20

01/11/99 -16.86 -16.91 -16.77 -17.20 -16.91 -13.78

01/26/99 -17.02 -16.71 -16.99 -17.15 -17.08 -13.74

02/24/99 -16.88 -16.98 -16.86 -17.04 -16.91 -13.46

03/10/99 -- -- -- -- -- --

04/07/99 -17.11 -17.21 -17.07 -17.31 -17.13 -13.75

05/19/99 -17.28 -17.36 -17.17 -17.50 -17.29 -13.86

07/16/99 -17.59 -17.70 -17.60 -17.79 -17.63 -14.33

08/25/99 -17.74 -17.75 -17.66 -17.86 -17.77 -14.49

11/16/99 -17.82 -17.92 -17.76 -17.94 -17.88 -14.69

12/28/99 -- -17.42 -17.32 -17.40 -17.40 -14.20

01/25/00 -16.19 -16.22 -16.07 -16.07 -16.18 -13.15

04/24/00 -16.72 -16.81 -16.77 -16.97 -16.81 -13.55

05/11/00 -17.12 -17.26 -17.14 -17.88 -17.27 -13.92

06/26/00 -17.52 -17.61 -17.52 -17.70 -17.58 -14.36

07/31/00 -17.73 -17.83 -17.72 -17.89 -17.81 -14.48

09/06/00 -17.93 -18.04 -17.92 -18.05 -18.04 -14.74

10/30/00 -17.64 -17.66 -17.62 -17.82 -17.18 -14.35

12/04/00 -17.52 -17.65 -17.51 -17.90 -17.61 -14.25

01/02/01 -17.44 -17.57 -17.44 -17.61 -17.53 -14.18

02/06/01 -17.28 -17.41 -17.22 -16.96 -17.37 -13.94

03/14/01 -17.13 -17.24 -17.08 -17.32 -17.13 -13.76

04/17/01 -17.29 -17.39 -17.49 -17.49 -17.35 -14.16

05/22/01 -17.23 -17.36 -17.24 -17.48 -17.27 -15.06

06/18/01 -17.38 -17.54 -17.37 -17.58 -17.46 -14.08

06/26/01 -- -17.61 -- -- -- --

07/16/01 -17.55 -17.67 -17.57 -17.79 -17.62 --

07/31/01 -- -17.83 -- -- -- --

08/20/01 -17.86 -17.98 -17.89 -18.06 -17.93 -14.53

09/20/01 -17.90 -18.01 -17.90 -18.07 -17.98 -14.67

Minimum* -17.93 -18.04 -17.92 -18.07 -18.04 -15.06

Median* -17.13 -17.31 -17.17 -17.40 -17.27 -13.93

Mean* -17.16 -17.28 -17.17 -17.38 -17.30 -13.95

Maximum* -15.17 -15.24 -15.24 -15.32 -15.99 -12.48

Table 2. Ground-water elevations on Twitchell Island, California, from September 1997 to September 2001—Continued
Table 3 25

Table 3. Well construction and estimates of hydraulic conductivity and transmissivity from slug tests for selected wells on Twitchell Island, California

Well name

Well

depth

Screened

interval

Sand pack 

interval

Grout

interval

Borehole

diameter

Casing

diameter

Hydraulic 

conductivity Transmissivity

(feet below land surface) (inches) (feet per day) (square feet per day)

peat (0–15 feet below land surface)

HDP 10 8–10 8–10 0–8 6 1.4 10.7

1Estimate made using the method developed by Papadopulos and others, 1973.

20.01

2Estimate made using the method developed by Bouwer and Rice, 1976.

 110 20.2

IDP 10 8–10 8–10 0–8 6 1.4 1.7 2.01 110 2.2

JDP 10 8–10 8–10 0–8 6 1.4 1.7 2.01 110 2.2

KDP 10 8–10 8–10 0–8 6 1.4 1.7 2.01 110 2.2

poorly sorted sand (20–30 feet below land surface)

HOW 27 25–27 23–27 0–23 6 2.2 19 25 1240 2150

IOW 25 23–25 21–25 0–21 6 2.2 19 25 1240 2150

JOW 27 25–27 23–27 0–23 6 2.2 19 25 1240 2150

KOW 27 25–27 23–27 0–23 6 2.2 19 25 1240 2150

silt (48–56 feet below land surface)

HMOW 60 52–55 50–57 0–50 6 2.2 11 20.5 170 230

fine silty sand (79–85 feet below land surface)

HDOW 88 80–83 78–85 0–78 6 2.2 15 22 1500 2100
26 Hydrogeologic Data from a Shallow Flooding Demonstration Project, Twitchell Island, California, 1997–2001

DAY

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP

October 1998 to September 1999

1 -- -- -- -- -- -- -- -- -- 0.26 0.25 0.24

2 -- -- -- -- -- -- -- -- -- 0.26 0.21 0.25

3 -- -- -- -- -- -- -- -- -- 0.26 0.20 0.25

4 -- -- -- -- -- -- -- -- -- 0.26 0.25 0.25

5 -- -- -- -- -- -- -- -- -- 0.25 0.25 0.25

6 -- -- -- -- -- -- -- -- -- 0.25 0.25 0.24

7 -- -- -- -- -- -- -- -- -- 0.26 0.20 0.25

8 -- -- -- -- -- -- -- -- -- 0.26 0.16 0.25

9 -- -- -- -- -- -- -- -- -- 0.26 0.16 0.24

10 -- -- -- -- -- -- -- -- -- 0.26 0.15 0.24

11 -- -- -- -- -- -- -- -- -- 0.26 0.15 0.24

12 -- -- -- -- -- -- -- -- -- 0.26 0.15 0.24

13 -- -- -- -- -- -- -- -- -- 0.26 0.16 0.24

14 -- -- -- -- -- -- -- -- -- 0.27 0.16 0.22

15 -- -- -- -- -- -- -- -- -- 0.27 0.15 0.08

16 -- -- -- -- -- -- -- -- -- 0.27 0.14 0.11

17 -- -- -- -- -- -- -- -- -- 0.26 0.15 0.36

18 -- -- -- -- -- -- -- -- -- 0.25 0.15 0.36

19 -- -- -- -- -- -- -- -- -- 0.18 0.15 0.36

20 -- -- -- -- -- -- -- -- -- 0.04 0.19 0.36

21 -- -- -- -- -- -- -- -- -- 0.15 0.22 0.35

22 -- -- -- -- -- -- -- -- -- 0.26 0.22 0.35

23 -- -- -- -- -- -- -- -- -- 0.25 0.22 0.34

24 -- -- -- -- -- -- -- -- -- 0.25 0.22 0.34

25 -- -- -- -- -- -- -- -- 0.26 0.25 0.24 0.34

26 -- -- -- -- -- -- -- -- 0.26 0.25 0.25 0.33

27 -- -- -- -- -- -- -- -- 0.26 0.24 0.25 0.33

28 -- -- -- -- -- -- -- -- 0.26 0.24 0.25 0.34

29 -- -- -- -- -- -- -- -- 0.26 0.25 0.25 0.33

30 -- -- -- -- -- -- -- -- 0.26 0.25 0.25 0.33

31 -- -- -- -- -- -- -- -- -- 0.25 0.24 --

Minimum* -- -- -- -- -- -- -- -- -- 0.04 0.14 0.08

Mean* -- -- -- -- -- -- -- -- -- 0.24 0.20 0.28

Maximum* -- -- -- -- -- -- -- -- -- 0.27 0.25 0.36

Table 4. Daily mean inflow at eastern inlet of East Pond at USGS site number 380626121383806 on Twitchell Island, California

[Daily mean values are calculated from hourly readings from micrometer installed on inlet valve; all shown in cubic feet per second. Values in bold indicate 

that one or more hourly readings were not included in the calculated daily mean due to equipment failure; --, missing data; *, statistical measures shown for 

information only; values may not be comparable due to missing data]
Table 4 27

DAY

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP

October 1999 to September 2000

1 0.33 0.23 0.44 -- -- -- -- -- -- -- -- --

2 0.33 0.39 0.42 -- -- -- -- -- -- -- -- --

3 0.32 0.38 0.42 -- -- -- -- -- -- -- -- --

4 0.32 0.38 -- -- -- -- -- -- -- -- -- --

5 0.31 0.41 -- -- -- -- -- -- -- -- -- --

6 0.32 0.13 -- -- -- -- -- -- -- -- -- --

7 0.32 -- 0.40 -- -- -- -- -- -- -- -- --

8 0.32 0.24 -- -- -- -- -- -- -- -- -- --

9 0.32 0.43 0.39 -- -- -- -- -- -- -- -- 0.50

10 0.32 0.43 -- -- -- -- -- -- -- -- -- 0.50

11 0.32 0.42 -- -- -- -- -- -- -- -- -- 0.50

12 0.32 0.27 -- -- -- -- -- -- -- -- -- 0.50

13 0.32 0.00 -- -- -- -- -- -- -- -- -- 0.50

14 0.33 -- -- -- -- -- -- -- -- -- -- 0.50

15 0.33 0.26 -- -- -- -- -- -- -- -- -- 0.50

16 0.31 0.42 -- -- -- -- -- -- -- -- -- 0.50

17 0.06 0.44 -- -- -- -- -- -- -- -- -- 0.50

18 -- 0.42 -- -- -- -- -- -- -- -- -- 0.49

19 0.16 0.21 -- -- -- -- -- -- -- -- 0.37 0.47

20 0.04 -- -- -- -- -- -- -- -- -- 0.36 0.50

21 0.15 -- -- -- -- -- -- -- -- -- 0.45 0.51

22 0.24 0.23 -- -- -- -- -- -- -- -- 0.48 0.50

23 0.08 0.44 -- -- -- -- -- -- -- -- 0.49 0.49

24 -- 0.44 -- -- -- -- -- -- -- -- 0.49 0.49

25 0.18 0.23 -- -- -- -- -- -- -- -- 0.49 0.50

26 0.24 0.27 -- -- -- -- -- -- -- -- 0.48 0.50

27 0.25 0.27 -- -- -- -- -- -- -- -- 0.48 0.50

28 0.26 -- -- -- -- -- -- -- -- -- 0.47 0.50

29 0.25 0.25 -- -- -- -- -- -- -- -- 0.46 0.50

30 0.03 0.43 -- -- -- -- -- -- -- -- 0.45 0.50

31 -- -- -- -- -- -- -- -- -- -- -- --

Minimum* 0.03 -- -- -- -- -- -- -- -- -- -- --

Mean* 0.25 -- -- -- -- -- -- -- -- -- -- --

Maximum* 0.33 -- -- -- -- -- -- -- -- -- -- --

Table 4. Daily mean inflow at eastern inlet of East Pond at USGS site number 380626121383806 on Twitchell Island, California—Continued
28 Hydrogeologic Data from a Shallow Flooding Demonstration Project, Twitchell Island, California, 1997–2001

DAY

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP

October 2000 to September 2001

1 0.50 0.27 0.26 0.15 0.12 0.14 0.17 0.16 0.25 0.24 0.22 0.36

2 0.50 0.28 0.22 0.14 0.12 0.14 0.17 0.18 -- 0.24 0.22 0.37

3 0.51 0.28 0.05 0.15 0.12 0.14 0.17 -- -- -- 0.22 0.36

4 0.51 0.28 0.06 0.15 0.12 0.14 0.17 -- 0.22 0.24 0.22 0.36

5 0.51 0.28 0.02 0.16 0.12 0.14 -- -- 0.22 0.24 0.22 0.33

6 0.51 0.28 0.01 0.16 0.12 0.14 -- -- 0.23 0.23 -- 0.33

7 0.52 0.28 0.31 0.17 0.12 0.14 0.22 0.16 0.22 0.24 0.22 0.33

8 0.51 0.28 0.09 0.17 0.12 0.14 0.16 0.19 0.22 0.24 0.22 0.33

9 0.51 0.28 0.09 0.17 0.12 0.15 0.19 0.22 0.23 0.24 0.22 0.33

10 0.51 0.28 0.07 0.15 0.12 0.15 0.18 0.25 0.23 0.24 0.22 0.33

11 0.51 0.27 0.06 0.11 0.12 0.15 0.13 0.24 0.23 0.24 0.21 0.32

12 0.51 0.27 0.15 0.11 0.12 0.14 0.12 0.24 0.23 0.24 0.21 0.32

13 0.51 0.27 0.24 0.11 0.12 0.17 0.12 0.23 0.22 0.24 0.20 --

14 0.51 0.26 0.23 0.11 0.12 0.17 0.14 0.26 0.22 0.22 0.21 --

15 0.51 0.26 0.24 0.11 0.13 0.17 0.14 0.23 0.22 0.22 0.21 --

16 0.51 0.25 0.24 0.11 0.13 0.17 0.18 0.23 0.29 0.21 0.20 0.22

17 0.50 0.28 0.23 0.14 0.13 0.18 0.18 0.24 0.48 0.22 -- --

18 0.26 0.28 0.21 0.13 0.13 0.18 0.18 0.23 0.36 0.23 0.20 0.18

19 0.26 0.28 0.20 0.13 0.13 0.19 0.19 0.24 0.22 0.23 0.19 0.19

20 0.25 0.27 0.20 0.14 0.13 0.19 0.19 0.23 0.23 0.23 -- --

21 0.25 0.28 0.20 0.14 0.14 0.19 -- 0.24 0.25 0.23 0.18 0.23

22 0.25 0.28 0.20 0.14 0.14 0.19 -- 0.23 0.24 0.22 0.19 0.25

23 0.24 0.19 0.20 0.14 0.14 0.20 -- 0.23 0.24 0.22 0.21 0.26

24 0.25 0.28 0.19 0.14 0.14 0.20 -- 0.24 0.24 0.22 0.21 --

25 0.26 0.19 0.19 0.13 0.14 0.20 -- 0.23 0.23 0.22 0.20 --

26 0.26 0.17 0.17 0.13 0.14 0.19 -- 0.23 0.23 0.22 0.21 0.25

27 0.26 0.14 0.15 0.13 0.14 0.18 -- 0.24 0.23 0.22 -- 0.25

28 0.26 0.17 0.15 0.13 0.15 0.17 -- 0.23 0.23 0.22 -- 0.25

29 0.26 0.19 0.15 0.13 -- 0.17 -- 0.23 0.23 0.22 -- 0.24

30 0.26 0.25 0.14 0.12 -- 0.16 -- 0.22 0.24 0.20 0.37 --

31 0.26 -- 0.15 0.12 -- 0.16 -- -- -- 0.20 -- --

Minimum* 0.24 0.14 0.01 0.11 0.12 0.14 -- -- 0.22 0.20 -- 0.18

Mean* 0.39 0.25 0.16 0.14 0.13 0.17 -- -- 0.25 0.23 -- 0.29

Maximum* 0.52 0.28 0.31 0.17 0.15 0.20 -- -- 0.48 0.24 -- 0.37

Table 4. Daily mean inflow at eastern inlet of East Pond at USGS site number 380626121383806 on Twitchell Island, California—Continued
Table 5 29

DAY

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP

October 1998 to September 1999

1 -- -- -- -- -- -- -- -- -- 0.51 0.50 0.50

2 -- -- -- -- -- -- -- -- -- 0.52 0.41 0.51

3 -- -- -- -- -- -- -- -- -- 0.52 0.39 0.51

4 -- -- -- -- -- -- -- -- -- 0.51 0.51 0.51

5 -- -- -- -- -- -- -- -- -- 0.50 0.50 0.51

6 -- -- -- -- -- -- -- -- -- 0.50 0.51 0.50

7 -- -- -- -- -- -- -- -- -- 0.51 0.39 0.51

8 -- -- -- -- -- -- -- -- -- 0.51 0.30 0.51

9 -- -- -- -- -- -- -- -- -- 0.51 0.28 0.50

10 -- -- -- -- -- -- -- -- -- 0.52 0.27 0.50

11 -- -- -- -- -- -- -- -- -- 0.52 0.27 0.50

12 -- -- -- -- -- -- -- -- -- 0.52 0.27 0.50

13 -- -- -- -- -- -- -- -- -- 0.52 0.28 0.49

14 -- -- -- -- -- -- -- -- -- 0.53 0.28 0.45

15 -- -- -- -- -- -- -- -- -- 0.53 0.27 0.16

16 -- -- -- -- -- -- -- -- -- 0.53 0.25 0.22

17 -- -- -- -- -- -- -- -- -- 0.51 0.23 0.75

18 -- -- -- -- -- -- -- -- -- 0.49 0.27 0.75

19 -- -- -- -- -- -- -- -- -- 0.32 0.26 0.75

20 -- -- -- -- -- -- -- -- -- 0.05 0.38 0.75

21 -- -- -- -- -- -- -- -- -- 0.31 0.43 0.73

22 -- -- -- -- -- -- -- -- -- 0.52 0.44 0.72

23 -- -- -- -- -- -- -- -- -- 0.52 0.45 0.72

24 -- -- -- -- -- -- -- -- -- 0.52 0.44 0.72

25 -- -- -- -- -- -- -- -- 0.51 0.51 0.49 0.71

26 -- -- -- -- -- -- -- -- 0.51 0.52 0.51 0.69

27 -- -- -- -- -- -- -- -- 0.51 0.47 0.51 0.68

28 -- -- -- -- -- -- -- -- 0.51 0.46 0.51 0.70

29 -- -- -- -- -- -- -- -- 0.52 0.51 0.51 0.69

30 -- -- -- -- -- -- -- -- 0.52 0.51 0.51 0.69

31 -- -- -- -- -- -- -- -- -- 0.51 0.50 --

Minimum* -- -- -- -- -- -- -- -- -- 0.05 0.23 0.16

Mean* -- -- -- -- -- -- -- -- -- 0.48 0.39 0.58

Maximum* -- -- -- -- -- -- -- -- -- 0.53 0.51 0.75

Table 5. Daily mean inflow at western inlet of East Pond at USGS site number 380626121383807 on Twitchell Island, California

[Daily mean values are calculated from hourly readings from micrometer installed on inlet valve and are shown in cubic feet per second. Values in bold 

indicate that one or more hourly readings were not included in the calculated daily mean due to equipment failure; --, missing data; *, statistical measures 

shown for information only; values may not be comparable due to missing data]
30 Hydrogeologic Data from a Shallow Flooding Demonstration Project, Twitchell Island, California, 1997–2001

DAY

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP

October 1999 to September 2000

1 0.36 0.17 -- -- -- -- -- -- -- -- 0.29 0.21

2 0.36 0.24 -- -- -- -- -- -- -- -- 0.29 0.22

3 0.35 0.23 -- -- -- -- -- -- -- -- -- 0.22

4 0.35 0.23 -- -- -- -- -- -- -- -- -- 0.22

5 0.35 0.26 -- -- -- -- -- -- -- -- 0.19 0.22

6 0.35 0.07 -- -- -- -- -- -- -- -- -- 0.25

7 0.35 -- -- -- -- -- -- -- -- -- -- 0.24

8 0.35 0.15 -- -- -- -- -- -- -- -- 0.14 0.21

9 0.35 0.22 -- -- -- -- -- -- -- -- -- 0.22

10 0.35 0.27 -- -- -- -- -- -- -- -- -- 0.21

11 0.35 0.25 -- -- -- -- -- -- -- -- 0.20 0.22

12 0.35 0.12 -- -- -- -- -- -- -- -- -- 0.22

13 0.34 -- -- -- -- -- -- -- -- -- -- 0.22

14 0.35 -- -- -- -- -- -- -- -- -- 0.25 0.22

15 0.36 0.12 -- -- -- -- -- -- -- -- 0.25 0.22

16 0.34 0.01 -- -- -- -- -- -- -- -- 0.25 0.23

17 0.05 0.08 -- -- -- -- -- -- -- -- 0.23 0.22

18 -- 0.06 -- -- -- -- -- -- -- -- 0.15 0.22

19 0.18 -- -- -- -- -- -- -- -- -- -- 0.20

20 0.03 -- -- -- -- -- -- -- -- -- -- 0.23

21 0.16 -- -- -- -- -- -- -- -- -- 0.19 0.22

22 0.26 0.06 -- -- -- -- -- -- -- -- 0.22 0.23

23 0.08 0.05 -- -- -- -- -- -- -- -- 0.22 0.23

24 -- 0.04 -- -- -- -- -- -- -- -- 0.22 0.23

25 0.20 0.00 -- -- -- -- -- -- -- -- 0.22 0.23

26 0.26 -- -- -- -- -- -- -- -- -- 0.22 0.23

27 0.26 -- -- -- -- -- -- -- -- 0.28 0.22 0.23

28 0.28 -- -- -- -- -- -- -- -- 0.29 0.22 0.23

29 0.26 -- -- -- -- -- -- -- -- 0.29 0.21 0.23

30 0.03 -- -- -- -- -- -- -- -- 0.29 0.20 0.23

31 -- -- -- -- -- -- -- -- -- 0.29 0.20 --

Minimum* 0.03 -- -- -- -- -- -- -- -- -- -- 0.20

Mean* 0.27 -- -- -- -- -- -- -- -- -- -- 0.22

Maximum* 0.36 -- -- -- -- -- -- -- -- -- -- 0.25

Table 5. Daily mean inflow at western inlet of East Pond at USGS site number 380626121383807 on Twitchell Island, California—Continued
Table 5 31

DAY

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP

October 2000 to September 2001

1 0.23 0.26 -- 0.14 0.15 0.15 0.25 0.18 -- 0.29 0.27 0.26

2 0.24 0.26 -- 0.14 0.16 0.14 0.25 0.20 -- -- 0.27 0.27

3 0.24 0.25 -- 0.14 0.15 0.14 0.25 0.20 -- -- 0.27 0.27

4 0.24 0.25 -- 0.14 0.16 0.14 0.25 0.20 0.23 -- 0.27 0.28

5 0.23 0.25 -- 0.14 0.16 0.14 -- 0.20 0.24 -- 0.27 0.32

6 0.23 0.25 -- 0.15 0.15 0.14 -- 0.21 0.25 -- 0.26 0.32

7 0.23 0.25 -- 0.15 0.15 0.14 -- -- 0.25 -- 0.26 0.32

8 0.23 0.25 -- 0.15 0.15 0.14 -- -- 0.25 -- 0.26 0.33

9 0.23 0.26 -- 0.15 0.15 0.14 0.14 0.27 0.25 -- 0.27 0.32

10 0.23 0.26 -- 0.15 0.16 0.14 0.13 0.27 0.25 -- 0.26 0.31

11 0.23 0.26 -- 0.14 0.16 0.13 0.12 0.26 0.25 -- 0.26 0.31

12 0.23 0.26 -- 0.13 0.16 0.13 0.12 0.23 0.25 -- 0.26 0.27

13 0.23 0.26 0.23 0.13 0.16 0.16 0.12 0.23 0.24 -- 0.24 --

14 0.23 0.26 0.22 0.13 0.16 0.19 0.11 0.23 0.24 -- 0.27 --

15 0.23 0.26 0.22 0.13 0.16 0.19 0.11 -- 0.25 -- 0.28 --

16 0.23 0.26 0.23 0.12 0.16 0.19 -- -- 0.21 -- 0.28 --

17 0.22 0.26 0.22 0.11 0.17 0.19 0.22 -- 0.10 -- 0.28 --

18 0.09 0.26 0.21 0.11 0.17 0.19 0.24 -- 0.14 -- 0.27 --

19 0.08 0.26 0.19 0.11 0.17 0.19 0.23 -- 0.26 0.25 0.26 --

20 0.08 0.26 0.19 0.11 0.17 0.19 0.23 -- 0.25 0.25 0.25 --

21 0.07 0.26 0.19 0.11 0.16 0.19 0.22 -- 0.28 0.26 0.25 --

22 0.07 0.26 0.19 0.11 0.17 0.25 0.21 -- 0.29 0.26 0.23 --

23 0.07 0.26 0.19 0.11 0.17 0.34 0.21 -- 0.28 0.25 0.21 --

24 0.16 0.26 0.20 0.11 0.16 0.34 0.21 -- 0.28 0.26 0.21 --

25 0.26 0.26 0.20 0.11 0.16 0.34 0.21 -- 0.29 0.26 0.21 --

26 0.26 0.26 0.17 0.11 0.16 0.31 0.21 -- 0.29 0.26 0.22 --

27 0.26 0.22 0.15 0.11 0.16 0.28 0.21 -- 0.29 0.26 0.23 --

28 0.26 -- 0.15 0.11 0.16 0.27 0.20 -- 0.29 0.26 0.26 --

29 0.26 -- 0.15 0.11 -- 0.26 0.20 -- 0.29 0.26 0.31 --

30 0.26 -- 0.15 0.13 -- 0.25 0.19 -- 0.29 0.21 0.31 --

31 0.26 -- 0.15 0.16 -- 0.25 -- -- -- 0.21 0.24 --

Minimum* 0.07 0.22 -- 0.11 0.15 0.13 -- -- 0.10 -- 0.21 --

Mean* 0.20 0.26 -- 0.13 0.16 0.20 -- -- 0.25 -- 0.26 --

Maximum* 0.26 0.26 -- 0.16 0.17 0.34 -- -- 0.29 -- 0.31 --

Table 5. Daily mean inflow at western inlet of East Pond at USGS site number 380626121383807 on Twitchell Island, California—Continued
32 Hydrogeologic Data from a Shallow Flooding Demonstration Project, Twitchell Island, California, 1997–2001

DAY

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP

October 1997 to September 1998

1 -- -- -- 0.02 0.43 0.10 0.44 -- 0.00 0.15 0.01 0.25

2 -- -- -- 0.01 0.41 0.09 -- -- 0.00 0.21 0.01 0.37

3 -- -- -- 0.02 0.40 0.09 -- -- 0.00 0.26 0.01 0.02

4 -- -- -- 0.02 0.38 0.08 -- -- 0.00 0.03 0.01 0.00

5 -- -- -- 0.02 0.37 0.07 -- -- 0.00 0.00 0.01 0.00

6 -- -- -- 0.02 0.36 0.06 -- -- 0.00 0.00 0.01 0.01

7 -- -- -- 0.03 0.34 0.06 -- -- 0.00 0.00 0.01 0.01

8 -- -- -- 0.03 0.33 0.05 -- -- 0.00 0.00 0.01 0.01

9 -- -- -- 0.03 0.32 0.04 -- -- -- 0.00 0.03 0.01

10 -- -- -- 0.03 0.30 0.04 -- -- -- 0.00 0.15 0.01

11 -- -- -- 0.04 0.29 0.03 -- -- 0.01 0.00 0.15 0.01

12 -- -- -- -- 0.28 0.03 -- -- 0.03 0.00 0.50 0.02

13 -- -- -- -- 0.27 0.02 -- -- 0.04 0.00 0.67 0.02

14 -- -- -- -- 0.26 0.02 -- -- 0.06 0.00 0.67 0.01

15 -- -- -- -- 0.24 0.01 -- -- 0.01 0.00 0.67 0.01

16 -- -- -- -- 0.23 0.01 -- -- 0.00 0.00 0.67 0.01

17 -- -- -- -- 0.22 0.01 -- -- 0.00 0.00 0.67 0.02

18 -- -- -- -- 0.21 0.00 -- -- 0.00 0.00 0.49 0.02

19 -- -- -- -- 0.20 0.00 -- -- 0.00 0.00 0.02 0.01

20 -- -- -- -- 0.19 0.01 -- -- 0.00 0.01 0.00 0.01

21 -- -- -- -- 0.18 0.02 -- -- 0.00 0.01 0.10 0.01

22 -- -- -- -- 0.17 0.03 -- -- 0.00 0.01 0.49 0.01

23 -- -- -- 0.57 0.16 0.05 -- 0.00 0.00 0.01 0.67 0.01

24 -- -- 0.01 0.55 0.15 0.07 -- 0.00 0.00 0.01 0.67 0.01

25 -- -- 0.01 0.54 0.14 0.09 -- 0.00 0.00 0.01 0.16 0.01

26 -- -- 0.01 0.52 0.13 0.10 -- 0.00 0.00 0.01 0.02 0.00

27 -- -- 0.01 0.50 0.12 0.08 -- 0.00 0.00 0.01 0.24 0.00

28 -- -- 0.01 0.49 0.11 0.05 -- 0.03 0.00 0.01 0.37 0.00

29 -- -- 0.01 0.47 -- 0.03 -- 0.01 0.28 0.01 0.52 0.00

30 -- -- 0.01 0.46 -- 0.03 -- 0.00 0.36 0.01 0.59 0.00

31 -- -- 0.02 0.44 -- 0.17 -- 0.00 -- 0.01 0.34 --

Minimum* -- -- -- -- 0.11 0.00 -- -- 0.00 0.00 0.00 0.00

Mean* -- -- -- -- 0.26 0.05 -- -- 0.03 0.02 0.29 0.03

Maximum* -- -- -- -- 0.43 0.17 -- -- 0.36 0.26 0.67 0.37

Table 6. Daily mean outflow at eastern outlet of East Pond at USGS site number 380626121383802 on Twitchell Island, California

[Daily mean values are calculated from hourly readings and are shown in cubic feet per second. Values in bold indicate that one or more hourly readings were 

not included in the calculated daily mean due to equipment failure; --, missing data; *, statistical measures shown for information only; values may not be 

comparable due to missing data]
Table 6 33

DAY

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP

October 1998 to September 1999

1 0.01 0.01 0.01 0.01 0.06 0.03 0.01 0.00 0.17 0.15 0.13 0.09

2 0.01 0.00 0.01 0.01 0.04 0.02 0.01 0.00 0.17 0.15 0.11 0.09

3 0.01 0.00 0.01 0.01 0.04 0.02 0.02 0.00 0.18 0.14 0.05 0.09

4 0.01 0.00 0.00 0.01 0.04 0.02 0.02 0.00 0.18 0.14 0.10 0.09

5 0.01 0.00 0.00 0.01 0.04 0.03 0.05 0.00 0.17 0.15 0.13 0.09

6 0.00 0.00 0.00 0.01 0.09 0.03 0.04 0.00 0.16 0.13 0.14 0.09

7 0.00 0.00 0.01 0.03 -- 0.03 0.02 0.00 0.15 0.13 0.12 0.10

8 0.00 0.00 0.01 0.03 -- 0.02 0.04 0.00 0.16 0.13 0.05 0.11

9 0.01 0.01 0.01 0.01 -- 0.01 0.00 0.00 0.16 0.14 0.03 0.11

10 0.01 0.01 0.01 0.01 -- 0.01 0.00 0.01 0.16 0.27 0.03 0.10

11 0.02 0.01 0.01 0.01 0.14 0.00 0.00 0.03 0.15 0.43 0.07 0.12

12 0.02 0.02 0.01 0.01 0.05 0.00 0.00 0.12 0.15 0.23 0.06 0.11

13 0.02 0.01 0.01 0.01 0.05 0.00 0.00 0.15 0.15 0.13 0.04 0.10

14 0.02 0.01 0.01 0.01 0.05 0.01 0.00 0.15 0.15 0.13 0.01 0.09

15 0.02 0.01 0.00 0.01 0.05 0.01 0.00 0.11 0.15 0.14 0.01 0.05

16 0.03 0.01 0.00 0.04 0.05 0.00 0.00 0.02 0.15 0.13 0.01 0.02

17 0.04 0.01 0.01 0.15 0.05 0.00 0.00 0.01 0.16 0.13 0.01 0.02

18 0.02 0.01 0.01 0.14 0.05 0.01 0.00 0.01 0.16 0.12 0.01 0.08

19 0.02 0.01 0.01 -- 0.04 0.01 0.00 0.10 0.15 0.07 0.01 0.15

20 0.03 0.01 0.01 0.16 0.04 0.10 0.00 0.17 0.15 0.01 0.01 0.17

21 -- 0.01 0.01 0.13 0.03 0.07 0.00 0.19 0.10 0.01 0.01 0.18

22 -- 0.01 0.01 0.10 0.03 0.02 0.00 0.18 0.12 0.01 0.01 0.17

23 0.34 0.01 0.01 0.08 0.03 0.06 0.00 0.18 0.15 0.04 0.02 0.15

24 0.26 0.01 0.01 0.07 0.03 0.01 0.00 0.19 0.16 0.11 0.02 0.14

25 0.20 0.01 0.01 0.07 0.06 0.07 0.00 0.20 0.16 0.13 0.05 0.14

26 0.15 0.01 0.01 0.07 0.05 0.01 0.00 0.20 0.16 0.13 0.14 0.13

27 0.10 0.01 0.01 0.04 0.03 0.01 0.00 0.18 0.16 0.12 0.28 0.12

28 0.05 0.01 0.01 0.05 0.02 0.01 0.00 0.18 0.16 0.09 0.34 0.11

29 0.02 0.01 0.01 0.05 -- 0.02 0.00 0.18 0.17 0.14 0.12 0.12

30 0.01 0.01 0.01 0.05 -- 0.02 0.00 0.18 0.17 0.14 0.10 0.12

31 0.01 -- 0.01 0.10 -- 0.02 -- 0.17 -- 0.13 0.09 --

Minimum* 0.00 0.00 0.00 0.01 -- 0.00 0.00 0.00 0.10 0.01 0.01 0.02

Mean* 0.05 0.01 0.01 0.05 -- 0.02 0.01 0.09 0.16 0.13 0.07 0.11

Maximum* 0.34 0.02 0.01 0.16 -- 0.01 0.05 0.20 0.18 0.43 0.34 0.18

Table 6. Daily mean outflow at eastern outlet of East Pond at USGS site number 380626121383802 on Twitchell Island, California—Continued
34 Hydrogeologic Data from a Shallow Flooding Demonstration Project, Twitchell Island, California, 1997–2001

DAY

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP

October 1999 to September 2000

1 0.12 0.00 0.08 -- -- -- -- 0.00 0.02 0.01 0.00 0.00

2 0.12 0.00 0.14 -- -- 0.36 -- 0.00 0.02 0.01 0.00 0.00

3 0.12 0.00 0.13 0.57 -- -- -- 0.00 0.02 0.01 0.00 0.00

4 0.11 0.00 0.08 0.41 -- -- -- 0.00 0.02 0.01 0.01 0.00

5 0.13 0.00 0.01 0.46 -- -- -- 0.00 0.02 0.01 0.01 0.00

6 0.12 0.01 0.01 0.48 -- -- -- 0.00 0.01 0.00 0.01 0.00

7 0.11 0.00 0.01 0.48 -- -- -- 0.00 0.01 0.00 0.01 0.00

8 0.10 0.00 0.09 -- -- -- -- 0.00 0.01 0.00 0.01 0.00

9 0.10 0.00 0.16 -- -- -- -- 0.00 0.01 0.01 0.01 0.00

10 0.09 0.04 0.17 -- -- 0.08 -- 0.00 0.01 0.01 0.01 0.00

11 0.09 0.01 0.13 -- -- 0.18 -- 0.00 0.01 0.01 0.01 0.00

12 0.08 0.04 0.02 0.45 -- 0.31 -- 0.00 0.01 0.01 0.01 0.00

13 0.09 0.00 0.02 0.40 -- -- -- 0.00 0.00 0.01 0.01 0.00

14 0.09 0.00 0.03 0.39 -- 0.30 -- 0.00 0.00 0.01 0.01 0.00

15 0.10 0.00 0.14 0.27 -- 0.05 -- 0.00 0.01 0.01 0.02 0.00

16 0.08 0.00 0.18 0.03 -- -- -- 0.00 0.21 0.01 0.47 0.01

17 0.03 0.01 0.19 0.10 -- -- -- 0.00 0.01 0.01 0.11 0.11

18 0.01 0.07 0.12 -- -- 0.21 -- 0.00 0.00 0.02 0.01 0.37

19 0.00 0.07 0.02 -- -- 0.01 -- 0.00 0.00 0.03 0.01 0.35

20 0.00 0.00 0.02 0.37 -- 0.00 -- 0.01 0.00 0.02 0.01 0.00

21 0.00 0.00 0.02 0.37 -- 0.01 -- 0.01 0.00 0.02 0.01 0.00

22 0.00 0.00 0.13 0.33 -- 0.15 -- 0.01 0.00 0.02 0.01 0.00

23 0.00 0.00 0.18 0.14 -- 0.00 0.26 0.01 0.00 0.02 0.01 0.00

24 0.00 0.00 0.20 -- -- 0.00 0.01 0.01 0.00 0.02 0.01 0.00

25 0.00 0.02 0.17 -- -- 0.31 0.01 0.01 0.01 0.02 0.01 0.01

26 0.00 0.00 0.11 -- -- -- 0.00 0.02 0.01 0.01 0.01 0.00

27 0.00 0.03 0.37 -- -- -- 0.00 0.02 0.01 0.00 0.01 0.00

28 0.00 0.01 -- -- -- -- 0.00 0.02 0.01 0.00 0.01 0.00

29 0.00 0.01 -- -- -- -- 0.00 0.01 0.01 0.00 0.01 0.01

30 0.00 0.01 -- -- -- -- 0.00 0.02 0.01 0.00 0.01 0.01

31 0.00 -- -- -- -- -- -- 0.02 -- 0.00 0.00 --

Minimum* 0.00 0.00 0.01 -- -- -- -- 0.00 0.00 0.00 0.00 0.00

Mean* 0.05 0.01 0.11 -- -- -- -- 0.01 0.02 0.01 0.03 0.03

Maximum* 0.13 0.10 0.37 -- -- -- -- 0.02 0.21 0.03 0.47 0.37

Table 6. Daily mean outflow at eastern outlet of East Pond at USGS site number 380626121383802 on Twitchell Island, California—Continued
Table 6 35

DAY

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP

October 2000 to September 2001

1 0.00 0.00 0.03 0.03 0.00 0.12 0.02 0.02 -- 0.11 0.05 0.06

2 0.01 0.00 0.04 0.03 0.00 0.19 0.02 0.01 -- 0.13 0.10 0.06

3 0.01 0.00 0.04 0.01 0.00 0.16 0.01 0.01 -- 0.22 0.08 0.05

4 0.00 -- 0.05 0.01 0.00 0.22 0.02 0.01 -- -- 0.09 0.03

5 0.00 -- 0.00 0.00 0.00 0.26 0.02 0.01 0.04 -- 0.07 0.04

6 0.00 -- 0.00 0.00 0.00 0.16 0.06 0.02 0.04 -- 0.05 0.04

7 0.00 -- 0.00 0.00 0.00 0.12 0.05 0.02 0.04 -- 0.05 0.05

8 0.00 -- 0.01 0.01 0.00 0.11 0.02 0.02 0.03 -- 0.04 0.05

9 0.00 -- 0.01 0.00 0.00 0.11 0.01 0.02 0.03 0.47 0.04 0.06

10 0.00 -- 0.01 0.02 0.00 0.10 0.01 0.02 0.03 -- 0.05 0.06

11 0.00 -- 0.01 0.01 0.00 0.10 0.01 0.02 0.03 0.10 0.10 0.06

12 0.00 -- 0.01 0.00 0.00 0.09 0.02 0.03 0.04 0.07 0.10 --

13 0.00 -- 0.01 0.00 0.07 0.08 0.02 0.04 0.03 0.07 0.09 --

14 0.00 -- -- 0.00 0.12 0.03 0.02 0.03 0.04 0.05 0.10 --

15 0.00 -- -- 0.00 0.12 0.02 0.01 0.03 0.06 0.05 0.11 --

16 0.00 -- -- 0.00 0.12 0.02 0.01 0.03 0.05 0.05 0.10 0.07

17 0.00 -- -- 0.00 0.12 0.02 0.01 0.02 0.07 0.05 0.09 0.12

18 0.00 -- -- 0.00 0.14 0.02 0.02 0.02 0.05 0.06 0.04 0.22

19 0.00 -- -- 0.00 0.16 0.02 0.02 0.02 0.04 0.06 0.04 0.18

20 0.00 -- -- 0.00 0.15 0.02 0.05 0.04 0.06 0.06 0.03 0.09

21 0.00 -- -- 0.00 0.18 0.02 0.04 0.04 0.09 0.06 0.03 0.07

22 0.00 -- -- 0.00 0.19 0.02 0.02 0.03 0.06 0.06 0.03 0.13

23 0.00 -- -- 0.00 0.22 0.05 0.02 0.03 0.05 0.05 0.03 0.23

24 0.00 0.00 -- 0.00 0.23 -- 0.02 0.03 0.05 0.06 0.03 0.24

25 0.00 0.00 -- 0.00 0.18 -- 0.02 0.02 0.08 0.10 0.03 0.11

26 0.00 0.00 -- 0.00 0.15 -- 0.02 0.03 0.14 0.07 0.03 0.05

27 0.00 0.00 -- 0.00 0.13 0.03 0.02 0.03 0.20 0.07 0.03 0.09

28 0.00 0.01 0.24 0.00 0.12 0.02 0.02 0.03 0.14 0.08 0.03 0.05

29 0.00 0.03 0.19 0.00 -- 0.02 0.02 0.03 0.08 0.08 0.05 0.06

30 0.00 0.03 0.03 0.00 -- 0.01 0.02 0.03 0.10 0.06 0.06 0.10

31 0.00 -- 0.03 0.00 -- 0.02 -- 0.03 -- 0.04 0.06 --

Minimum* 0.00 -- -- 0.00 0.00 0.01 0.01 0.01 0.03 -- 0.03 0.03

Mean* 0.00 -- -- 0.01 0.09 0.08 0.02 0.02 0.06 -- 0.06 0.09

Maximum* 0.01 -- -- 0.03 0.23 0.26 0.06 0.04 0.20 -- 0.11 0.24

Table 6. Daily mean outflow at eastern outlet of East Pond at USGS site number 380626121383802 on Twitchell Island, California—Continued
36 Hydrogeologic Data from a Shallow Flooding Demonstration Project, Twitchell Island, California, 1997–2001

DAY

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP

October 1997 to September 1998

1 -- -- -- 0.00 0.00 -- 0.22 -- 0.06 0.01 0.25 0.35

2 -- -- -- 0.00 0.04 -- -- -- 0.08 0.01 0.23 0.37

3 -- -- -- 0.01 -- -- -- -- 0.13 0.01 0.22 0.34

4 -- -- -- 0.01 -- -- -- -- 0.17 0.01 0.27 0.31

5 -- -- -- 0.01 -- -- -- -- 0.18 0.01 0.33 0.32

6 -- -- -- 0.01 -- -- -- -- 0.22 0.01 0.23 0.32

7 -- -- -- 0.01 -- -- -- -- 0.25 0.01 0.35 0.31

8 -- -- -- 0.01 -- -- -- -- 0.28 0.02 0.41 0.28

9 -- -- -- 0.01 -- -- -- -- -- 0.01 0.43 0.32

10 -- -- -- 0.01 -- -- -- -- -- 0.02 0.45 0.32

11 -- -- -- 0.01 -- -- -- -- 0.36 0.05 0.41 0.32

12 -- -- -- 0.07 -- -- -- -- 0.34 0.25 -- 0.31

13 -- -- -- -- -- -- -- -- 0.27 0.34 -- 0.31

14 -- -- -- -- -- -- -- -- 0.22 0.35 -- 0.30

15 -- -- -- -- -- -- -- -- 0.15 0.34 -- 0.32

16 -- -- -- -- -- -- -- -- 0.15 0.32 -- 0.33

17 -- -- -- -- -- 0.10 -- -- 0.14 0.20 -- 0.32

18 -- -- -- -- -- 0.09 -- -- 0.12 0.26 0.47 0.33

19 -- -- -- -- -- 0.09 -- -- 0.20 0.26 0.39 0.35

20 -- -- -- -- -- 0.07 -- -- 0.20 0.26 0.37 0.34

21 -- -- -- -- -- 0.06 -- -- 0.21 0.25 0.38 0.34

22 -- -- -- -- -- 0.05 -- -- 0.22 0.30 0.49 0.34

23 -- -- -- -- -- 0.04 -- 0.29 0.22 0.22 -- 0.34

24 -- -- -- -- -- 0.04 -- 0.15 0.22 0.10 -- 0.34

25 -- -- -- -- -- 0.14 -- 0.05 0.16 0.16 0.36 0.36

26 -- -- -- -- -- -- -- 0.00 0.11 0.28 0.34 0.38

27 -- -- -- -- -- -- -- 0.00 0.15 0.28 0.38 0.40

28 -- -- -- -- -- -- -- 0.00 0.12 0.26 0.38 0.39

29 -- -- -- 0.00 -- -- -- 0.00 0.08 0.25 0.42 0.36

30 -- -- -- 0.00 -- -- -- 0.02 0.02 0.24 0.44 0.36

31 -- -- -- 0.00 -- 0.14 -- 0.03 -- 0.28 0.35 --

Minimum* -- -- -- -- -- -- -- -- 0.02 0.01 -- 0.28

Mean* -- -- -- -- -- -- -- -- 0.18 0.17 -- 0.34

Maximum* -- -- -- -- -- -- -- -- 0.36 0.35 -- 0.40

Table 7. Daily mean outflow at western outlet of East Pond at USGS site number 380626121383801 on Twitchell Island, California

[Daily mean values are calculated from hourly readings and are shown in cubic feet per second. Values in bold indicate that one or more hourly readings were 

not included in the calculated daily mean due to equipment failure; --, missing data; *, statistical measures shown for information only; values may not be 

comparable due to missing data]
Table 7 37

DAY

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP

October 1998 to September 1999

1 0.36 0.40 0.39 0.34 0.26 0.28 0.42 0.02 0.06 0.10 0.06 0.07

2 0.37 0.37 0.35 0.34 0.24 0.23 0.43 0.01 0.06 0.10 0.05 0.08

3 0.36 0.36 0.35 0.34 0.25 0.14 0.45 0.01 0.06 0.09 0.01 0.08

4 0.36 0.33 0.25 0.33 0.25 0.24 0.43 0.00 0.07 0.11 0.04 0.08

5 0.36 0.33 0.32 0.29 0.23 0.27 0.43 0.00 0.06 0.11 0.06 0.09

6 0.39 0.33 0.35 0.21 0.32 0.27 0.46 0.00 0.05 0.10 0.07 0.09

7 0.41 0.49 0.32 0.23 -- 0.24 0.41 0.00 0.05 0.10 0.05 0.08

8 0.41 0.48 0.33 0.23 -- 0.14 0.47 0.00 0.05 0.10 0.00 0.08

9 0.40 0.35 0.30 0.23 -- 0.39 0.43 0.00 0.04 0.10 0.00 0.08

10 0.41 0.34 0.31 0.23 -- 0.30 0.40 0.00 0.05 0.22 0.00 0.08

11 0.41 0.35 0.31 0.23 0.24 0.32 0.25 0.01 0.04 0.36 0.03 0.08

12 0.42 0.32 0.33 0.22 0.09 0.32 0.05 0.06 0.05 0.18 0.02 0.07

13 0.44 0.31 0.34 0.24 0.03 0.33 0.03 0.07 0.06 0.10 0.02 0.07

14 0.45 0.31 0.34 0.27 0.03 0.34 0.02 0.07 0.06 0.11 0.00 0.06

15 0.46 0.32 0.34 0.31 0.02 0.32 0.11 0.04 0.07 0.11 0.00 0.03

16 0.43 0.32 0.35 0.34 0.03 0.25 0.11 0.00 0.07 0.12 0.00 0.01

17 0.45 0.35 0.36 0.31 0.13 0.29 0.00 0.00 0.07 0.10 0.00 0.01

18 0.49 0.32 0.36 0.39 0.14 0.32 0.00 0.00 0.06 0.11 0.00 0.05

19 0.52 0.30 0.34 0.30 0.13 0.41 0.00 0.03 0.06 0.06 0.00 0.13

20 0.51 0.27 0.33 0.19 0.16 0.43 0.03 0.07 0.06 0.01 0.00 0.14

21 -- 0.28 0.31 0.15 0.18 0.46 0.08 0.08 0.04 0.01 0.00 0.14

22 -- 0.29 0.34 -- 0.08 0.43 0.01 0.07 0.04 0.01 0.00 0.15

23 0.66 0.30 0.33 0.14 0.07 -- 0.11 0.07 0.08 0.02 0.00 0.14

24 -- 0.34 0.32 0.17 0.19 0.43 0.01 0.08 0.09 0.07 0.00 0.13

25 -- 0.32 0.32 0.18 0.31 0.54 0.08 0.08 0.09 0.08 0.01 0.14

26 0.58 0.32 0.32 0.24 0.29 0.42 0.07 0.07 0.09 0.08 0.06 0.13

27 0.56 0.37 0.32 0.20 0.29 0.39 0.06 0.07 0.10 0.07 0.16 0.12

28 0.53 0.40 0.32 0.22 0.29 0.39 0.05 0.06 0.10 0.04 0.21 0.12

29 0.50 0.37 0.32 0.24 -- 0.40 0.04 0.07 0.10 0.06 0.08 0.14

30 0.44 0.44 0.33 0.25 -- 0.41 0.03 0.07 0.11 0.06 0.08 0.14

31 0.42 -- 0.34 0.35 -- 0.43 -- 0.07 -- 0.05 0.07 --

Minimum* 0.36 0.27 0.25 0.14 -- 0.14 0.00 0.00 0.04 0.01 0.00 0.01

Mean* 0.45 0.35 0.33 0.26 -- 0.34 0.19 0.04 0.07 0.09 0.03 0.09

Maximum* 0.66 0.49 0.39 0.39 -- 0.54 0.47 0.08 0.11 0.36 0.21 0.15

Table 7. Daily mean outflow at western outlet of East Pond at USGS site number 380626121383801 on Twitchell Island, California—Continued
38 Hydrogeologic Data from a Shallow Flooding Demonstration Project, Twitchell Island, California, 1997–2001

DAY

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP

October 1999 to September 2000

1 0.12 0.00 0.07 -- -- -- -- 0.01 0.00 0.00 0.00 0.00

2 0.12 0.00 0.12 0.53 0.39 0.25 -- 0.01 0.00 0.00 0.00 0.00

3 0.13 0.00 0.12 0.31 -- 0.31 -- 0.01 0.00 0.00 0.00 0.00

4 0.12 0.00 0.08 0.18 -- -- -- 0.01 0.00 0.00 0.01 0.00

5 0.12 0.00 0.01 0.23 -- -- -- 0.01 0.00 0.01 0.01 0.00

6 0.12 0.01 0.01 0.25 -- -- -- 0.01 0.00 0.01 0.01 0.00

7 0.11 0.00 0.01 0.26 -- -- -- 0.01 0.00 0.01 0.01 0.00

8 0.11 0.00 0.08 0.58 -- -- -- 0.01 0.00 0.01 0.01 0.00

9 0.13 0.00 0.15 -- -- -- -- 0.01 0.00 0.01 0.01 0.00

10 0.13 0.03 0.17 -- -- 0.07 -- 0.01 0.00 0.01 0.01 0.00

11 0.13 0.08 0.14 -- -- 0.14 -- 0.00 0.00 0.00 0.01 0.00

12 0.13 0.03 0.02 0.32 -- 0.27 -- 0.00 0.00 0.01 0.01 0.00

13 0.13 0.00 0.02 0.30 -- -- -- 0.00 0.00 0.00 0.01 0.00

14 0.13 0.00 0.03 0.30 -- -- -- 0.00 0.00 0.00 0.01 0.00

15 0.12 0.00 0.13 0.21 -- 0.19 -- 0.00 0.00 0.00 0.01 0.00

16 0.09 0.00 0.18 0.02 -- -- -- 0.00 0.10 0.00 0.28 0.03

17 0.03 0.01 0.19 0.04 -- -- -- 0.00 0.00 0.00 0.04 0.09

18 0.01 0.07 0.11 -- -- 0.12 -- 0.00 0.00 0.00 0.01 0.29

19 0.01 0.07 0.02 0.39 -- 0.02 -- 0.00 0.00 0.00 0.00 0.29

20 0.00 0.00 0.02 0.33 -- 0.11 -- 0.00 0.00 0.00 0.00 0.18

21 0.00 0.00 0.02 0.32 -- 0.24 -- 0.00 0.00 0.01 0.00 0.20

22 0.00 0.00 0.10 0.30 -- 0.30 -- 0.00 0.00 0.02 0.00 0.18

23 0.00 0.00 0.17 0.11 -- 0.28 0.30 0.00 0.00 0.03 0.00 0.13

24 0.00 0.00 0.20 -- -- 0.28 0.07 0.00 0.00 0.03 0.01 0.12

25 0.00 0.01 0.17 -- -- 0.38 0.04 0.00 0.00 0.03 0.01 0.08

26 0.00 0.00 0.04 -- -- -- 0.02 0.00 0.00 0.02 0.01 0.04

27 0.00 0.02 0.22 -- -- -- 0.02 0.00 0.00 0.01 0.01 0.02

28 0.00 0.01 0.46 -- -- -- 0.02 0.00 0.00 0.02 0.00 0.02

29 0.00 0.01 0.63 -- -- -- 0.02 0.00 0.00 0.03 0.00 0.06

30 0.00 0.01 -- -- -- -- 0.01 0.00 0.00 0.02 0.00 0.09

31 0.00 -- -- -- -- -- -- 0.00 -- 0.01 0.00 --

Minimum* 0.00 0.00 0.01 -- -- -- -- 0.00 0.00 0.00 0.00 0.00

Mean* 0.06 0.01 0.13 -- -- -- -- 0.00 0.00 0.01 0.02 0.06

Maximum* 0.13 0.08 0.63 -- -- -- -- 0.01 0.10 0.03 0.28 0.29

Table 7. Daily mean outflow at western outlet of East Pond at USGS site number 380626121383801 on Twitchell Island, California—Continued
Table 7 39

DAY

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP

October 2000 to September 2001

1 0.08 0.36 0.46 0.13 0.10 0.00 0.25 0.17 0.20 0.271 0.26 0.28

2 0.06 0.37 0.45 0.12 0.10 0.00 0.24 0.15 -- 0.271 0.27 0.28

3 0.05 0.39 0.44 0.13 0.11 0.00 0.24 0.14 -- 0.286 0.26 0.27

4 0.04 0.00 0.46 0.10 0.11 0.01 0.22 0.16 0.18 0.333 0.27 0.25

5 0.03 0.00 0.49 0.09 0.12 0.01 0.18 0.18 0.19 -- 0.27 0.27

6 0.02 0.00 0.48 0.10 0.11 0.00 0.25 0.17 0.20 -- 0.26 0.28

7 0.01 0.34 0.49 0.12 0.10 0.00 0.29 0.18 0.23 -- 0.27 0.28

8 0.01 0.00 0.23 0.19 0.09 0.00 0.29 0.18 0.22 0.483 0.26 0.28

9 0.01 0.00 0.09 0.16 0.13 0.00 0.20 0.17 0.22 0.332 0.26 0.29

10 0.04 0.36 0.10 0.18 0.18 0.00 0.18 0.17 0.23 0.343 0.26 0.30

11 0.06 -- 0.12 0.17 0.20 0.00 0.19 0.16 0.24 0.279 0.25 0.29

12 0.04 -- 0.19 0.10 0.19 0.00 0.20 0.16 0.25 0.284 0.25 --

13 0.01 -- 0.16 0.07 0.08 0.15 0.20 0.17 0.22 0.281 0.24 --

14 0.01 -- -- 0.06 0.00 0.21 0.21 0.16 0.22 0.261 0.25 --

15 0.01 -- -- 0.05 0.00 0.18 0.21 0.16 0.23 0.259 0.27 --

16 0.01 -- -- 0.04 0.00 0.16 0.21 0.17 0.24 0.254 0.33 0.30

17 0.01 -- -- 0.04 0.00 0.16 0.20 0.17 0.28 0.263 0.26 0.12

18 0.01 -- -- 0.04 0.00 0.16 0.20 0.14 0.26 0.26 0.26 0.05

19 0.01 -- -- 0.05 0.00 0.17 0.20 0.14 0.24 0.27 0.28 0.32

20 0.01 -- -- 0.05 0.00 0.17 0.25 0.11 0.22 0.28 0.27 0.31

21 0.01 -- -- 0.05 0.00 0.17 0.27 0.15 0.26 0.27 0.25 0.31

22 0.01 -- -- 0.08 0.00 0.18 0.23 0.17 0.26 0.27 0.25 0.09

23 0.05 -- -- 0.11 0.00 0.23 0.22 0.15 0.26 0.26 0.25 0.04

24 0.12 0.33 -- 0.14 0.01 0.25 0.22 0.15 0.26 0.27 0.26 0.26

25 0.29 0.22 -- 0.16 0.00 -- 0.21 0.15 0.27 0.27 0.25 0.41

26 0.47 0.08 -- 0.19 0.00 0.32 0.21 0.17 0.30 0.27 0.25 0.32

27 0.40 0.18 -- 0.12 0.00 0.30 0.20 0.19 0.31 0.27 0.24 0.24

28 0.42 0.37 0.00 0.09 0.00 0.29 0.21 0.18 0.30 0.27 0.24 0.31

29 0.42 0.45 0.23 0.09 -- 0.28 0.20 0.18 0.28 0.26 0.25 0.29

30 0.42 0.45 0.19 0.08 -- 0.27 0.19 0.18 0.27 0.23 0.27 0.18

31 0.38 -- 0.15 0.09 -- 0.26 -- 0.18 -- 0.22 0.28 --

Minimum* 0.01 -- -- 0.04 0.00 0.00 0.18 0.11 0.18 0.22 0.24 0.04

Mean* 0.11 -- -- 0.10 0.06 0.13 0.22 0.16 0.24 0.28 0.26 0.25

Maximum* 0.47 -- -- 0.19 0.20 0.32 0.29 0.19 0.31 0.48 0.33 0.41

Table 7. Daily mean outflow at western outlet of East Pond at USGS site number 380626121383801 on Twitchell Island, California—Continued
40 Hydrogeologic Data from a Shallow Flooding Demonstration Project, Twitchell Island, California, 1997–2001

Date Inflow Outflow Change in 

storage Seepage

10/01/00 0.74 -0.13 -- --

10/02/00 0.74 -0.11 -0.09 0.54

10/03/00 0.74 -0.01 0.03 0.68

10/04/00 0.75 -0.08 0.15 0.81

10/05/00 0.75 -0.07 0.06 0.74

10/06/00 0.75 -0.06 -0.06 0.62

10/07/00 0.75 -0.05 0.03 0.72

10/08/00 0.74 -0.05 0.03 0.73

10/09/00 0.74 -0.02 0.00 0.72

10/10/00 0.91 -0.05 0.09 0.96

10/11/00 0.77 -0.07 0.18 0.89

10/12/00 0.74 -0.06 0.09 0.77

10/13/00 0.73 -0.04 0.09 0.78

10/14/00 0.74 -0.05 -0.09 0.60

10/15/00 0.74 -0.04 -0.12 0.58

10/16/00 0.73 -0.04 -0.06 0.64

10/17/00 0.72 -0.04 -0.09 0.59

10/18/00 0.35 -0.04 -0.48 -0.18

10/19/00 0.33 -0.04 -0.06 0.24

10/20/00 0.33 -0.04 0.09 0.38

10/21/00 0.32 -0.07 0.12 0.37

10/22/00 0.31 -0.08 0.57 0.80

10/23/00 0.31 -0.09 0.39 0.62

10/24/00 0.41 -0.15 0.03 0.28

10/25/00 0.55 -0.30 0.24 0.49

10/26/00 0.69 -0.48 0.45 0.67

10/27/00 0.52 -0.42 0.03 0.13

10/28/00 0.63 -0.42 -0.18 0.03

10/29/00 0.52 -0.43 -0.15 -0.06

10/30/00 0.58 -0.43 -0.18 -0.03

10/31/00 0.52 -0.41 0.00 0.11

11/01/00 0.52 -0.38 -0.03 0.11

11/02/00 0.54 -0.39 -0.21 -0.07

11/03/00 0.53 -0.42 0.09 0.21

11/25/00 0.45 -0.22 0.27 0.50

Date Inflow Outflow Change in 

storage Seepage

11/26/00 0.43 -0.08 -0.03 0.31

11/27/00 0.36 -0.18 -0.30 -0.12

12/29/00 0.30 -0.42 0.15 0.03

12/30/00 0.29 -0.23 -0.06 0.00

12/31/00 0.30 -0.18 0.03 0.15

01/01/01 0.29 -0.16 -0.03 0.10

01/02/01 0.29 -0.16 -0.03 0.10

01/03/01 0.29 -0.14 0.03 0.17

01/04/01 0.29 -0.12 0.21 0.38

01/05/01 0.30 -0.11 0.00 0.19

01/06/01 0.31 -0.12 0.06 0.25

01/07/01 0.32 -0.13 0.00 0.19

01/08/01 0.43 -0.20 -0.15 0.08

01/09/01 0.32 -0.17 0.00 0.15

01/10/01 0.42 -0.21 -0.03 0.18

01/11/01 0.29 -0.18 -0.18 -0.07

01/12/01 0.24 -0.13 -0.33 -0.21

01/13/01 0.25 -0.09 0.21 0.36

01/14/01 0.23 -0.09 -0.15 -0.00

01/15/01 0.23 -0.09 0.00 0.14

01/16/01 0.23 -0.08 0.12 0.28

01/17/01 0.24 -0.07 0.24 0.42

01/18/01 0.24 -0.06 -0.24 -0.06

01/19/01 0.24 -0.07 -0.09 0.08

01/20/01 0.25 -0.07 0.09 0.27

01/21/01 0.25 -0.07 0.00 0.18

01/22/01 0.26 -0.10 0.03 0.18

01/23/01 0.34 -0.12 0.00 0.22

01/24/01 0.26 -0.17 0.03 0.12

01/25/01 0.38 -0.17 0.00 0.21

01/26/01 0.24 -0.21 0.00 0.03

01/27/01 0.24 -0.15 -0.06 0.03

01/28/01 0.23 -0.11 -0.03 0.09

01/29/01 0.25 -0.11 -0.03 0.10

01/30/01 0.25 -0.11 0.00 0.14

Table 8. Water budget for East Pond, October 2000 to September 2001, on Twitchell Island, California

[Seepage is the sum of inflows, outflows, and change in storage. Negative values indicate subsurface discharge into the pond. Values shown in cubic feet 

per second; *, statistics calculated only on dates when all daily mean values included 24 hourly readings and all measurements were within instrument 

range; --, no measurement was made on that date]
Table 8 41

Date Inflow Outflow Change in 

storage Seepage

01/31/01 0.27 -0.12 -0.03 0.12

02/01/01 0.27 -0.12 0.00 0.15

02/02/01 0.27 -0.12 0.00 0.15

02/07/01 0.27 -0.15 0.00 0.12

02/08/01 0.27 -0.13 0.03 0.17

02/09/01 0.35 -0.14 0.18 0.38

02/10/01 0.33 -0.20 0.09 0.22

02/11/01 0.37 -0.22 0.03 0.18

02/12/01 0.34 -0.20 0.00 0.14

02/13/01 0.28 -0.19 -0.03 0.06

02/14/01 0.29 -0.16 -0.03 0.10

02/15/01 0.29 -0.16 -0.03 0.10

02/16/01 0.29 -0.16 0.00 0.13

02/17/01 0.31 -0.15 0.00 0.16

02/18/01 0.30 -0.18 0.00 0.13

02/19/01 0.33 -0.20 0.03 0.16

02/20/01 0.31 -0.18 -0.03 0.10

02/21/01 0.35 -0.22 0.03 0.16

02/24/01 0.42 -0.28 0.00 0.15

02/25/01 0.30 -0.23 -0.06 0.00

02/26/01 0.30 -0.19 -0.03 0.08

02/27/01 0.31 -0.19 0.00 0.11

02/28/01 0.31 -0.18 -0.03 0.10

03/05/01 0.31 -0.28 0.06 0.09

03/06/01 0.28 -0.19 -0.03 0.05

03/07/01 0.29 -0.15 0.06 0.19

03/08/01 0.29 -0.14 0.03 0.18

03/09/01 0.29 -0.15 -0.09 0.05

03/10/01 0.28 -0.14 -0.03 0.11

03/11/01 0.28 -0.12 -0.03 0.13

03/12/01 0.28 -0.13 -0.03 0.12

03/13/01 0.33 -0.27 -0.03 0.03

03/14/01 0.36 -0.27 0.00 0.09

03/15/01 0.36 -0.22 0.00 0.14

03/16/01 0.36 -0.22 -0.03 0.11

Date Inflow Outflow Change in 

storage Seepage

03/17/01 0.37 -0.21 -0.09 0.06

03/18/01 0.37 -0.21 -0.03 0.13

03/19/01 0.37 -0.22 -0.03 0.12

03/20/01 0.38 -0.22 -0.03 0.12

03/21/01 0.38 -0.22 0.00 0.16

03/22/01 0.45 -0.24 0.00 0.21

03/23/01 0.53 -0.32 0.00 0.21

03/27/01 0.46 -0.38 0.00 0.08

03/30/01 0.41 -0.33 -0.03 0.05

03/31/01 0.41 -0.33 0.00 0.08

04/01/01 0.42 -0.32 0.00 0.10

04/02/01 0.42 -0.29 0.00 0.12

04/03/01 0.41 -0.29 0.00 0.12

04/04/01 0.42 -0.27 0.27 0.42

04/10/01 0.35 -0.24 -0.06 0.05

04/11/01 0.28 -0.25 0.00 0.03

04/12/01 0.31 -0.25 0.03 0.09

04/13/01 0.30 -0.25 -0.03 0.01

04/14/01 0.23 -0.26 0.00 -0.03

04/15/01 0.23 -0.27 -0.03 -0.07

04/17/01 0.36 -0.25 0.00 0.10

04/18/01 0.38 -0.26 0.00 0.12

04/19/01 0.41 -0.26 0.00 0.15

04/20/01 0.52 -0.31 0.00 0.21

04/21/01 0.40 -0.34 0.00 0.05

04/22/01 0.40 -0.29 0.00 0.11

04/23/01 0.40 -0.28 0.06 0.17

05/01/01 0.33 -0.29 0.00 0.05

05/02/01 0.38 -0.29 0.00 0.09

05/09/01 0.50 -0.28 0.00 0.21

05/10/01 0.53 -0.28 -0.03 0.22

05/11/01 0.50 -0.28 -0.09 0.13

05/12/01 0.47 -0.27 0.00 0.21

05/13/01 0.46 -0.28 0.00 0.18

05/14/01 0.49 -0.29 0.00 0.20

Table 8. Water budget for East Pond, October 2000 to September 2001, on Twitchell Island, California—Continued
42 Hydrogeologic Data from a Shallow Flooding Demonstration Project, Twitchell Island, California, 1997–2001

Date Inflow Outflow Change in 

storage Seepage

06/08/01 0.48 -0.33 -0.06 0.08

06/09/01 0.48 -0.33 0.06 0.21

06/10/01 0.47 -0.33 0.06 0.20

06/11/01 0.48 -0.34 -0.03 0.11

06/12/01 0.48 -0.36 0.03 0.15

06/13/01 0.46 -0.33 0.36 0.49

06/14/01 0.46 -0.33 0.00 0.13

06/15/01 0.47 -0.37 -0.15 -0.05

06/16/01 0.50 -0.36 -0.24 -0.10

06/17/01 0.59 -0.43 0.06 0.22

06/18/01 0.50 -0.40 0.00 0.10

06/19/01 0.48 -0.36 0.00 0.12

06/20/01 0.48 -0.36 0.09 0.21

06/21/01 0.53 -0.43 -0.09 0.01

06/22/01 0.53 -0.41 0.12 0.24

06/23/01 0.53 -0.39 -0.03 0.11

06/24/01 0.52 -0.39 0.18 0.31

06/25/01 0.55 -0.40 -0.27 -0.13

06/26/01 0.52 -0.49 0.06 0.08

06/27/01 0.53 -0.53 -0.12 -0.12

06/28/01 0.52 -0.51 0.12 0.13

06/29/01 0.52 -0.44 -0.03 0.05

06/30/01 0.52 -0.46 0.03 0.01

07/01/01 0.54 -0.46 0.12 0.19

08/01/01 0.49 -0.38 0.03 0.14

08/10/01 0.48 -0.38 0.33 0.43

08/11/01 0.47 -0.42 0.21 0.27

08/12/01 0.47 -0.41 -0.09 -0.03

08/13/01 0.44 -0.39 -0.27 -0.22

08/24/01 0.42 -0.35 0.09 0.16

09/03/01 0.64 -0.38 -0.09 0.17

Minimum*0.23 -0.53 -0.33 -0.21

Mean* 0.47 -0.21 0.01 0.26

Median* 0.47 -0.17 0.03 0.18

Maximum*0.91 -0.04 0.36 0.96

Table 8. Water budget for East Pond, October 2000 to September 2001, on Twitchell Island, California—Continued