U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2020-5029

Benthic Vertical Hydraulic Gradients in Upper Klamath 

Lake, Oregon, 2017
Cover: Water-level monitoring equipment deployed at site ON03 in Upper Klamath 

Lake, Oregon, viewed looking northwest. (Photograph taken by Jim Kuwabara, U.S. 

Geological Survey, August 2, 2017.)
Benthic Vertical Hydraulic Gradients in 

Upper Klamath Lake, Oregon, 2017

By Nicholas T. Corson-Dosch

Scientific Investigations Report 2020–5029

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DAVID BERNHARDT, Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2020

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Suggested citation:

Corson-Dosch, N.T., 2020, Benthic vertical hydraulic gradients in Upper Klamath Lake, Oregon, 2017: U.S. Geological 

Survey Scientific Investigations Report 2020–5029, 22 p., https://doi.org/ 10.3133/ sir20205029.

ISSN 2328-0328 (online)
iii

Contents

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

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

Study Area..............................................................................................................................................2

Background and Previous Work ........................................................................................................2

Purpose and Scope ..............................................................................................................................4

Methods and Datasets ..................................................................................................................................4

Study Design and Sites ........................................................................................................................4

Piezometers and Stilling Wells ...........................................................................................................5

Continuous Water-Level Data .............................................................................................................7

Discrete Water-Level Data ..................................................................................................................7

Vertical Hydraulic Gradient .................................................................................................................8

Uncertainty.............................................................................................................................................8

Data Summary................................................................................................................................................8

Water Levels..........................................................................................................................................8

Vertical Hydraulic Gradient ...............................................................................................................10

Conclusion.....................................................................................................................................................20

Acknowledgments.......................................................................................................................................20

References Cited..........................................................................................................................................21

Figures

1. Map showing locations of groundwater piezometer and stilling well paired sets

at 10 sites on Upper Klamath Lake, Oregon, 2017 ...................................................................3

2. Schematic diagram of the groundwater piezometer and lake stilling well

apparatus deployed at 10 locations and detail view of the recording pressure

transducer configuration with the common measuring point for groundwater

and lake depth-to-water measurements ..................................................................................6

3. Graph showing barometric pressure at the Rocky Point gage, Upper Klamath

Lake, Oregon, 2017 ........................................................................................................................7

4. Graphs showing measured groundwater and lake depth to water below the

measuring point and calculated vertical hydraulic gradient at site SPR in Upper

Klamath Lake, Oregon, 2017 ......................................................................................................11

5. Graphs showing groundwater and lake depth to water below the measuring

point and calculated vertical hydraulic gradient at site LN01 in Upper Klamath

Lake, Oregon, 2017 ......................................................................................................................12

6. Graphs showing groundwater and lake depth to water below measuring the

point and vertical hydraulic gradient (VHG) at site ON02 in Upper Klamath Lake,

Oregon, 2017 ................................................................................................................................13

7. Graphs showing groundwater and lake depth to water below the measuring

point and vertical hydraulic gradient (VHG) at site ON03 in Upper Klamath Lake,

Oregon, 2017 ................................................................................................................................14

8. Graphs showing groundwater and lake depth to water below the measuring

point and vertical hydraulic gradient at site LC01 in Upper Klamath Lake,

Oregon, 2017 ................................................................................................................................15
iv

Figures—Continued

20

16

17

18

19

Tables

1. Site locations and deployment durations, Upper Klamath Lake, Oregon, 2017 ..................5

2. Continuous data collection and mean vertical hydraulic gradient (VHG) during

each week and during the study period at each site, Upper Klamath Lake,

Oregon, 2017 ..................................................................................................................................9
v

Conversion Factors

U.S. customary units to International System of Units

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square foot (ft2) 929.0 square centimeter (cm2)

square foot (ft2) 0.09290 square meter (m2)

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2)

Volume

ounce, fluid (fl. oz) 0.02957 liter (L)

pint (pt) 0.4732 liter (L)

quart (qt) 0.9464 liter (L)

gallon (gal) 3.785 liter (L)

cubic inch (in3) 0.01639 liter (L)

cubic foot (ft3) 28.32 cubic decimeter (dm3)

cubic foot (ft3) 0.02832 cubic meter (m3)

Flow rate

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

Datum

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Abbreviations

MP measuring point

UKL Upper Klamath Lake

USGS U.S. Geological Survey

VHG vertical hydraulic gradient

Benthic Vertical Hydraulic Gradients in Upper Klamath 

Lake, Oregon, 2017

By Nicholas T. Corson-Dosch

Abstract

Groundwater piezometers and lake stilling wells were 

deployed as paired sets at 10 locations in Upper Klamath 

Lake in south-central Oregon from May to October 2017 to 

measure hydraulic heads in and beneath the lake. Continuous 

water-level data from piezometers and stilling wells were 

then used to calculate the vertical hydraulic gradient (VHG) 

across the sediment-water interface to determine the direction 

and relative magnitude of the movement of water between 

the lake and underlying sediments. Over the study period, 

heads in lake-bed sediments closely tracked lake levels, both 

decreasing from spring into autumn. Instantaneous VHG was 

highly dynamic at all sites and exhibited high-frequency (less 

than 1 day to less than 1 hour) variations in magnitude and 

direction. Instantaneous and weekly mean VHG values often 

exceeded, but were commonly within, the range of measurement uncertainty (VHG less than +0.009 foot per foot [ft/

ft] and greater than -0.009 ft/ft). 63 percent of instantaneous 

VHG values and 66 percent of weekly mean VHG values 

were within this range. Study period mean VHG was within 

measurement uncertainty at seven of the nine sites that had 

continuous water-level data, but two littoral sites (LC03 and 

LS01) had positive (upward) values greater than measurement 

uncertainty and are likely locations of vertical groundwater 

seepage. Data collected in this study provide new information 

about the hydraulic conditions at the sediment-water interface 

in UKL and demonstrate that sediment-groundwater exchange 

in UKL is spatially and temporally heterogeneous.

Introduction

Upper Klamath Lake (UKL), in south-central Oregon, 

is naturally eutrophic1 and receives nutrients from internal 

(groundwater inflow, lakebed sediment) and external (tributary 

1Eutrophication is a natural process that results from an overabundance 

of nutrients—primarily nitrogen and phosphorus—in lakes or other bodies 

of water. Algae feed on the nutrients, and proliferate in blooms—growing, 

spreading, and turning the water green. When the algae die, they are decomposed by bacteria. This process consumes oxygen and can deplete dissolved 

oxygen levels in the water body creating a state of hypoxia.

streams, runoff, atmospheric deposition) sources (Oregon 

Department of Environmental Quality, 2002). Anthropogenic 

changes to the basin have increased nutrient delivery to UKL, 

and in recent decades, the lake has experienced annual cyanobacterial algal blooms during summer (Bortleson and Fretwell, 

1993; Kann and others, 2015). UKL is now hypereutrophic 

(U.S. Fish and Wildlife Service, 2012). Algal blooms contribute to severe water-quality problems in UKL, including low 

and high dissolved-oxygen concentrations, high pH, and high 

ammonia concentrations (Wood and others, 2006). These conditions stress endangered fish species in the lake (specifically 

short-nose suckers [Chasmistes brevirostris] and Lost River 

suckers [Deltistes luxatus]) and affect water quality downstream in the Klamath River (Saiki and others, 1999; Sullivan 

and others, 2013).

Understanding and addressing water-quality problems in 

UKL requires an accurate account of the flows of water and 

nutrients into and out of the lake. Previously published waterbalance estimates indicate that groundwater inflow to the lake 

represents about 15 percent of the total lake inflow (Hubbard, 

1970; Bureau of Reclamation, 2005; Walker and others, 2012). 

An unknown proportion of this groundwater is from seepage 

through the lakebed, which could transport nutrients from the 

groundwater system to the lake water column. Kuwabara and 

others (2009; 2016) suggest that groundwater inflow through 

lakebed sediments may be an important mechanism for lake 

nutrient loading. This concept is difficult to evaluate, however, 

because little is known about the distribution and magnitude of possible groundwater inflow, or about how inflow of 

solutes with groundwater may relate to algal bloom dynamics. 

Understanding and quantifying groundwater inflow into UKL 

is hampered by a lack of information on the controlling physical parameters such as vertical hydraulic gradients (VHG) and 

sediment hydraulic conductivity.

The U.S. Geological Survey (USGS) began a study in 

2017 to collect information about vertical hydraulic gradients 

in UKL. Vertical hydraulic gradients were directly measured beneath UKL in spring and summer, the period when 

cyanobacterial blooms occur. Ten sites in UKL (fig. 1) were 

instrumented to measure shallow lakebed groundwater levels 

and lake water levels during spring through autumn 2017. 

Groundwater and lake water-level data were used to calculate 

VHG at these locations. VHG can be used to characterize 

the direction and relative magnitude of groundwater-lake 
2 Benthic vertical hydraulic gradients in Upper Klamath Lake, Oregon, 2017

exchange at each site. Hydrologic data collected in the study 

and documented in this report can be used to refine UKL water 

and nutrient budgets and to better define the spatial and temporal distribution of groundwater-lake water exchange in UKL.

Study Area

UKL (fig. 1) is in south-central Oregon about 15 miles 

north of the Oregon-California border and 11 miles east of 

the Cascade Range crest. The lake is in the Klamath Graben, 

a down-dropped structural valley bounded by northwesttrending faults and steep, high escarpments. The UKL drainage basin is about 3,800 square miles (mi2) and spans the 

boundary between the Cascade Range and the Basin and 

Range geologic provinces (Leonard and Harris, 1974). The 

geology of the basin is characterized by highly permeable 

volcanic rock and volcanically derived, phosphorus-rich soils 

(Wood and others, 2006; Gannett and others, 2007). UKL is 

underlain by thick accumulations of basin-fill deposits and 

lake sediments (clay, silt, sand and diatomite) estimated to be 

1,300–4,000 feet (ft) thick (Gannett and others, 2012).

UKL is large, shallow, and relatively well mixed. The 

surface area of the lake ranges from about 100 to 140 mi2

depending on lake stage (Hubbard, 1970; Johnson and others, 

1985). The mean water depth in UKL is 9 ft, and about 90 

percent of the lake is less than 12 ft (Wood and others, 2006). 

The primary source of water to the lake is the Williamson 

River, which supplies about 46 percent of the total lake inflow 

(Johnson and others, 1985). UKL also receives water from 

other tributary streams, agricultural return flows, springs, 

precipitation, and direct groundwater seepage.

Although UKL is a natural water body, lake stage has 

been regulated since 1921, when Link River Dam was constructed at the lake’s outlet. Since 2001, in accordance with 

the Endangered Species Act, the U.S. Bureau of Reclamation 

has been required to maintain lake elevations at certain levels 

to protect habitat for endangered fish species in UKL. At the 

same time, water must be released from UKL at the Link 

River Dam to achieve specified flows in the Klamath River 

for salmon, which are federally listed as a threatened species 

(National Research Council, 2008; Gannett and others, 2012). 

Water from UKL and the Upper Klamath River is also the primary supply for the Bureau of Reclamation Klamath Project, 

an irrigation system that provides water to approximately 375 

mi2 of farm and ranch land in the Upper Klamath Basin (Wood 

and others, 2006). The combined effects of these uses, coupled 

with reduced summer inflow in tributaries and evapotranspiration from the lake surface, cause the lake elevation to decrease 

about 5 ft from spring to autumn (Wood and others, 2006; 

Gannett and others, 2012).

The uplands surrounding UKL are recharge areas for 

the regional groundwater flow system. Groundwater head 

gradients to the north, east, and west of the lake slope toward 

UKL from the uplands (Gannett and others, 2007). There are 

also strong upward vertical head gradients adjacent to UKL, 

particularly to the north in the lower Wood River Valley where 

there are many flowing artesian wells (Snyder and Morace, 

1997). These head gradients, along with the presence of 

springs on the lake margin, indicate that there is the potential 

for groundwater seepage to UKL through lakebed sediments.

Background and Previous Work

Upper Klamath Lake water-quality problems associated 

with annual algae blooms, combined with numerous and often 

competing demands for lake water, have motivated a wide 

range of environmental studies and monitoring in the Upper 

Klamath basin. An accurate water balance is needed to inform 

resource management and for scientific understanding of the 

lake. Several studies have estimated the UKL water balance 

(Hubbard, 1970; Cooper, 2004; Bureau of Reclamation, 2005; 

Walker and others, 2012). In these studies, the sum of known 

and estimated lake outflows and lake storage change was 

subtracted from the sum of known and estimated lake inflows. 

A general lake water-balance equation is:

SWin +GWin + PRECIP = SWout + ET ± ∆ S, (1)

where

SWin is the inflow of surface water;

GWin is the inflow of groundwater;

PRECIP is precipitation;

SWout is the outflow of surface water;

ET is evapotranspiration; and

ΔS is the change in water stored in the lake.

The groundwater component (GWin) in equation 1 represents the combined inflow from springs and direct groundwater seepage through the lake bottom. GWin is difficult to 

measure directly. If the other components (SWin, PRECIP, 

SWout, ET, and ΔS) of the water balance are known or estimated, GWin can be estimated as the residual sum of the other 

components. There is considerable uncertainty, however, 

in estimating groundwater inflow using the water-balance 

residual approach (Walker and others, 2012). The residual 

value includes the sum of all errors in the estimates of the 

other water-balance components.

Past estimates of the groundwater component of the 

UKL water balance have been made using the water-balance 

residual. Despite the inherent uncertainty of this method, the 

different studies that have applied it are generally in good 

agreement. Hubbard (1970) produced a monthly water balance 

for UKL for water years2 1965–1967 and estimated an average monthly groundwater inflow of 350 cubic feet per second 

(ft3/s), about 15 percent of an average annual lake inflow of 

2,330 ft3/s during the period of measurement. Cooper (2004)

compared UKL inflows and outflows and the difference 

between the two compares well with Hubbard’s groundwater inflow value (Gannett and others, 2007). The Bureau of 

2A water year is defined as the 12-month period Beginning October 1, for 

any given year and continuing through September 30, of the following year.
Introduction 3

Upper Klamath 

Lake

Agency 

Lake

Williamson River

Aspen

Lake

Algoma

Altamont

Shady Pine

Modoc Point

Rocky Point

Pelican City

Terminal City

Klamath

Falls

Recreation

(historical)

Clover Station (historical)

Ouxy Spring

97

97

140

140

70

62

ON01

SPR

LS01

OS03

OC02

LC01 LC03

ON03 ON02

LN01

Map

area

OREGON

ON01

ON03 Recorder site

Discrete site

EXPLANATION

122°00' 121°50'

42°

30'

42°

20'

Base map modified from The National Map and other digital resources. 

Coordinate reference system: WGS 1984 UTM Zone 10N. Map area in Klamath 

County. Horizontal datum is North American Datum of 1983. 0 5 KILOMETERS

0 5 MILES

Figure 1. Locations of groundwater piezometer and stilling well paired sets at 10 sites on Upper Klamath Lake, Oregon, 2017. 

[Continuous data was recovered at nine sites (recorder sites). At ON01, only discrete water-level measurements collected during 

site visits were available [discrete site].
4 Benthic vertical hydraulic gradients in Upper Klamath Lake, Oregon, 2017

Reclamation (2005) produced a revised groundwater inflow 

estimate of 320 ft3/s using updated lake stage-volume curves. 

Walker and others (2012) calculated a water budget for water 

years 1992–2010 and estimated an average groundwater 

inflow of approximately 310 ft3/s, about 18 percent of an average annual total lake inflow of 1,780 ft3/s during the period of 

the study. Although GWin represents the combined inflow from 

springs and direct groundwater seepage, the total measured 

discharge from springs around the margins of UKL is much 

less than estimates of GWin, meaning that an unknown portion 

of this inflow likely comes from direct groundwater seepage 

through the lakebed (Gannett and others, 2007).

The flows of water into and out of the lake also transport 

dissolved and particulate nutrients. Substantial work has been 

done to study UKL nutrient fluxes (Kann and Walker, 2001; 

Oregon Department of Environmental Quality, 2002; Walker, 

2001; Walker and others, 2012; Wood and others, 2013), but 

the relative importance of one such flux—nutrient transport by 

groundwater advection through the lakebed sediment—is not 

well constrained. Several recent studies have sought to examine this flux by combining nutrient concentration data with 

estimated rates of biological, diffusive, and advective solute 

transport across the sediment-water interface. Kuwabara and 

others (2009; 2012; 2016) found that nutrient concentrations 

in UKL lakebed sediment pore-water were often greater than 

in the overlying lake water. Kuwabara and others (2009; 2016) 

used observed vertical temperature profile data from five locations (one in 2005 and four in 2015) to estimate groundwater 

flux across the lake-sediment interface using heat-flux modeling. These estimates of groundwater flux varied temporally but 

were mostly upward (from sediment to lake). Based on these 

results, Kuwabara and others (2016) suggest that advective 

transport by groundwater inflow may be an important source 

of nutrients to the water column of UKL. These studies had 

large uncertainty because of the lack of reliable vertical head 

gradient information.

Purpose and Scope

In 2017, the USGS began studying vertical head gradients beneath UKL, critical to a quantitative understanding 

of groundwater-lake exchange. Groundwater and lake water 

levels were measured at 10 sites distributed across UKL during May through October 2017. Water-level data were used to 

calculate VHG across the sediment-water interface. The calculated VHG values provide new information about the spatial 

and temporal distribution of exchange in UKL and can be used 

to define the direction and relative magnitude of groundwaterlake exchange flow at each site.

The scope of this report is (1) a description of the methods used to measure groundwater and lake water levels; (2) a 

summary of groundwater and lake water-level measurements; 

(3) a documentation of the calculation of VHG using groundwater and lake water-level measurements; and (4) a summary

of VHG data.

Methods and Datasets

This report describes two datasets collected by the USGS. 

The first is continuous water-level data from groundwater 

piezometers and lake stilling wells at specific sites within 

UKL. The second is discrete field measurements of water 

levels in groundwater piezometers and lake stilling wells relative to common measurement points (MPs), which were used 

to verify the accuracy of the continuous water-level data. This 

report also describes the VHG at each site, which was calculated using the continuous water-level data. The methods and 

equipment used to collect these data and calculate VHG are 

described in this section.

Study Design and Sites

To understand the spatial and temporal distribution of 

VHG it is necessary to determine the head (water level) in the 

lake relative to the head in the underlying sediments. Head 

in the underlying sediments was determined by installing 

piezometers in the lakebed. The piezometers were open to a 

discrete interval below the bottom of the lake but were closed 

to the lake itself. Differences between the water level in the 

piezometer, which represents the groundwater head, and the 

lake level, represent the VHG.

Groundwater piezometer and lake stilling well paired sets 

were deployed at 10 sites (fig. 1) distributed across northern, 

central, and southern parts of UKL. Equipment was deployed 

on May 2 and 3, 2017, and was removed on September 27 

and October 5, 2017. The spring –autumn study period was 

designed to capture the full extent of the UKL seasonal waterlevel decline and hydraulic conditions before, during, and after 

the 2017 cyanobacterial bloom.

The 10 locations selected for this study corresponded to 

sites that have been previously used for other environmental 

monitoring projects (Kuwabara and others, 2016; StaufferOlsen and others, 2017). The established naming convention 

for these sites was used in this study for consistency with 

earlier work. Sites were classified as either littoral (near shore 

and lake water depth less than 6 ft during spring) or openwater (lake water depth greater than 6 ft during spring) and 

assigned an “L” or “O,” respectively. Based on their position 

in UKL, sites were then classified into three approximately 

equal-area geographic sectors: north, central, and south. Sites 

in each sector were assigned an “N,” “C,” or “S,” respectively. Two-digit serial numbers (starting at 01 and increasing sequentially) were added to the end of each site name to 

distinguish between sites in the same geographic sector with 

similar water depths. For example, a littoral site in the northern sector of the lake was named “LN01,” a second littoral site 

in the northern sector was named “LN02,” and an open-water 

site from the southern sector of the lake was named “OS01.” 

One additional site, positioned offshore from Ouxy Spring (on 
Methods and Datasets 5

the eastern edge of the lake), was named “SPR,” as it had been 

in previous studies. In this report, SPR is considered an openwater site.

Data collection was interrupted several times. The 

piezometer pipe at LN01 was found damaged on May 31, 

2017, and was removed, repaired, and redeployed on June 22, 

2017. Due to the limited discrete check measurements available before the damage occurred, only data after redeployment data at LN01 has been published. Piezometers deployed 

at ON02, SPR, and OC02 were lost within 2 weeks of initial 

deployment due to wave action, equipment failure, or vandalism. New equipment was redeployed at ON02 and SPR on 

June 26, 2017, and at OC02 on July 12, 2017. The equipment 

at ON01 was lost between site visits on August 1 and 15, 

2017. Equipment was not redeployed at ON01; therefore, only 

discrete data collected before August 1, 2017 were available at 

this site for this report. Complete site and equipment deployment information is presented in table 1.

Piezometers and Stilling Wells

The feasibility of deploying equipment to continuously 

monitor shallow groundwater and lake water levels was demonstrated by Kuwabara and others (2016). This study used a 

paired piezometer and stilling well design like that described 

by Kuwabara and others (2016), with minor adjustments to 

allow for periodic field water-level measurements and to 

improve transducer stability (fig. 2). Groundwater piezometer 

and lake-level stilling well paired sets deployed at each site 

were secured together with stainless steel band clamps. The 

piezometer was constructed with a section of 1-inch (in) diameter galvanized steel pipe, connected by a galvanized steel 

reducer coupling to a section of 0.75-in diameter galvanized 

steel pipe, which was threaded into a Solinst 0.75-in stainless steel model 615 drive-point piezometer well point with 

a 12-in long screen. The length of the 1-in diameter pipe was 

adjusted according to the water depth at each site so that there 

was 2 ft of pipe above the surface of the water at the time of 

deployment. Piezometer deployment depth was controlled by 

a 15.75-in square, 0.4-in thick, polyvinyl chloride (PVC) base 

plate with a 1-in diameter hole drilled in its center. The base 

Table 1. Site locations and deployment durations, Upper Klamath Lake, Oregon, 2017.

[Sites were classified as either littoral (lake water depth less than 6 ft during spring) or open-water (lake water depth greater than 6 ft during spring). 

Abbreviations: NAD 83, North American Datum of 1983; ––, equipment was lost during deployment and not recovered]

Site U.S. Geological 

Survey site No. Site type Habitat type

Lake 

sector

Latitude 

(NAD 83)

Longitude 

(NAD 83)

Date 

equipment 

deployed

Date equipment 

retrieved

LN01

422922122001301 Groundwater

Littoral North 42.48951 -122.00369 May 2, 2017 October 5, 2017 422922122001300 Lake

ON01

422519121531201 Groundwater Open 

water North 42.40510 -122.02060 May 2, 2017 –– 422519121531200 Lake

ON03

422614122023801 Groundwater Open 

water North 42.43721 -122.04386 May 2, 2017 October 5, 2017 422614122023800 Lake

ON02

422612121581701 Groundwater Open 

water North 42.43655 -121.97142 June 26, 

2017 October 5, 2017 422612121581700 Lake

LC01

422736121555001 Groundwater

Littoral Central 42.46010 -121.93056 June 22, 

2017

September 27, 

422736121555000 Lake 2017

LC03

422740121543101 Groundwater

Littoral Central 42.46121 -121.90869 May 3, 2017 September 27,

422740121543100 Lake 2017

SPR

422354121493101 Groundwater Open 

water Central 42.39842 -121.82523 June 26, 

2017 October 5, 2017 422354121493100 Lake

OC02

422502121510301 Groundwater Open 

water Central 42.41734 -121.85075 July 12, 

2017 October 5, 2017 422502121510300 Lake

OS03

421906121540401 Groundwater Open 

water South 42.31841 -121.90110 May 3, 2017 October 5, 2017 421906121540400 Lake

LS01

422014121561301 Groundwater

Littoral South 42.33709 -121.93687 May 3, 2017 October 5, 2017 422014121561300 Lake
6 Benthic vertical hydraulic gradients in Upper Klamath Lake, Oregon, 2017

plate was slid onto and clamped to the 1-in diameter steel pipe 

4.92 ft above the bottom of the piezometer screen. During 

deployment, the piezometers were manually driven into the 

lakebed sediment off the side of a boat. The base plates rested 

on the lakebed, providing stability to the equipment, and controlling the depth to which the piezometer screens extended 

into the lakebed sediment. Piezometer screens were set at 3.92 

through 4.92 ft below the lakebed at all locations. This depth 

interval was selected for consistency with earlier studies that 

used lakebed sediment temperature data over the interval 4.92 

ft below the lakebed to model groundwater fluxes (Kuwabara 

and others, 2009; Kuwabara and others, 2016). Immediately 

following deployment, about 5 liters (L) of water were rapidly 

added to the piezometers to flush fines away from the piezometer screen and thereby improve the hydrologic connection 

with the lakebed sediment.

The lake-level stilling wells were constructed out of 2-in 

diameter schedule 40 PVC. The wells were designed to have 

2 ft of pipe above the lake surface at the time of deployment 

in May and at least 2 ft of pipe below the lake surface at low 

stage in October. To meet these design requirements, and to 

accommodate a conservatively estimated 6 ft of lake-level 

drop between equipment deployment and removal, 10-ft-long 

stilling well pipes were used. A perforated 2-in PVC end cap 

was attached to the bottom of the stilling well for hydrologic 

connection to the lake. The perforated cap was screened with 

copper mesh to reduce biofouling on transducers installed 

within the stilling well pipe.

Recording pressure transducers were deployed inside 

all piezometers and stilling wells. Transducers were hung on 

vinyl-coated stainless-steel wires attached to stainless-steel 

locking pins. The pins were installed horizontally through 

holes drilled into the piezometer and stilling well casings 

(fig. 2). The top 3-ft sections of the piezometer and stilling 

well pipe were designed to be removed mid-deployment so 

that, as lake elevation dropped, increasing amounts of pipe 

above the lake surface would not prevent the collection of 

depth to water measurements by boat. Removal of the upper 

sections would also prevent the piezometer apparatus from 

becoming top-heavy and unstable. The top sections of the 

piezometers and stilling wells were removed on August 25th 

and 30th, 2017. The pressure transducers were briefly removed 

from the wells during this process and were replaced on shortened wires once the pipe adjustment was completed.

Locking pin

Locking pin

Groundwater 

piezometer 

(steel)

Groundwater 

piezometer 

(steel)

Lake stilling

well (PVC)

Lake stilling

well (PVC)

Stainless steel cable 

attached to submersible 

transducers

Lake 

(UKL)

Sediment

Piezometer screen 

Lakebed

3.92 feet 

below lakebed

4.92 feet 

below lakebed

Removable 

top sections

Perforated 

end cap

A B

Common measuring point (MP)

Figure 2. (A) Schematic diagram of the groundwater piezometer and lake stilling well apparatus deployed at 

10 locations and (B) detail view of the recording pressure transducer configuration with the common measuring 

point for groundwater and lake depth-to-water measurements, Upper Klamath Lake, 2017. [The groundwater 

piezometer screen was open to the lakebed sediment from 3.92 to 4.92 feet below the lakebed surface. The 

stilling well was open to the lake. Schematic diagram is not to scale. Schematic detail view is not to scale. PVC, 

polyvinyl chloride]
Methods and Datasets 7

Continuous Water-Level Data

Piezometers and stilling wells were instrumented with 

Solinst Edge Model 3001 Levelogger unvented pressure transducers. The transducers recorded sensor depth at 10-minute 

intervals. Barometric pressure was recorded at the Rocky 

Point lake gage (USGS site 11505800 [Upper Klamath Lake at 

Rocky Point, OR]) with a Solinst 3001 Barologger, which was 

set to record at the same interval as the water-level transducers (fig. 3). The continuous water-level data was corrected for 

barometric pressure by subtracting the barometric pressure 

reading from the sensor-depth reading. The corrected sensordepth readings were converted to values of depth below MP 

using the field-measured depth to water value collected at the 

time of sensor deployment.

Some drift was observed during portions of the continuous data record likely caused by changes in well and logger 

position from the effects of waves and wind. Drift offset 

corrections were applied to the continuous water-level data to 

ensure good agreement (±0.02 ft) with periodic field-measured 

water levels. The magnitudes of the corrections were commonly 0.01–0.03 ft. An offset correction was applied to the 

time-series data after the top-section removal to account for 

any change in sensor position within the well. Spikes in the 

water-level time-series data associated with site visits were 

also removed from the continuous record. Portions of the 

continuous water-level data from four groundwater pressure transducers (LN01, ON02, ON03, LC01) could not be 

reasonably corrected to match field verification measurements. 

These data were removed from the continuous record. In all 

instances, these periods of unusable data began after several 

months of reliable data had been collected. It is possible that 

the systematic deviations in the raw transducer readings were 

the result of low battery or sensor fouling. Discrete field waterlevel measurements have been reported where continuous data 

from one sensor was unusable.

Discrete Water-Level Data

Water levels were measured from a boat during site visits 

at approximately 2-week intervals using a calibrated electric 

water-level tape (Waterline, 150 ft Coax Water Level Meter). 

These measurements were used to verify the accuracy of the 

transducer readings and, if necessary, to correct the continuous water-level data. At each site, water levels were measured 

in the piezometer and stilling well relative to a common 

MP (fig. 2). MPs were marked on the top of the galvanized 

pipe at each paired set. Repeat measurements were collected 

to confirm original readings according to the methods of 

Cunningham and Schalk (2011). MPs were not surveyed to a 

vertical datum due to the distance of the wells from shore and 

the prohibitive difficulty of surveying well elevations from a 

boat. For calculating VHG at each location, water-level measurements relative to a common datum (in this case, a common 

MP) were considered sufficient. To minimize measurement 

error, discrete water-level measurements were not collected 

when there was strong wind or wave action. The water-level 

tape used to collect field measurements was calibrated by the 

USGS Hydrologic Instrumentation Facility. Tape calibration 

adjustments (equal to -0.01 ft for all measurements) were 

applied to raw field-collected water-level measurements.

May June July August September October

2017

28.8

29.0

29.2

29.4

29.6

Barometric pressure, in feet water

EXPLANATION

Upper Klamath Lake at 

Rocky Point, OR

Figure 3. Barometric pressure at the Rocky Point gage, Upper Klamath Lake, Oregon, 2017. [U.S. Geological 

Survey site number 11505800 (Upper Klamath Lake at Rocky Point, OR)]
8 Benthic vertical hydraulic gradients in Upper Klamath Lake, Oregon, 2017 

Vertical Hydraulic Gradient

Vertical hydraulic gradient was calculated by dividing 

the difference between the depth to water in the groundwater 

piezometer and the depth to water in the lake stilling well 

(equal to the difference in hydraulic head across the sedimentwater interface) by the vertical distance between the midpoint 

of the piezometer screen and the lakebed (equation 2).

(

 DTWgw − DTWlake)

 ____________ l= VHG, (2)

where 

DTWgw is the depth to water in the groundwater 

piezometer;

DTWlake is the depth to water in the lake stilling well;

l is the vertical distance between the midpoint

of the piezometer screen and the lakebed 

(in this study, l was equal to 4.42 ft at all 

locations); and

VHG is the vertical hydraulic gradient.

VHG was calculated at each location where reliable data were 

simultaneously available for both the piezometer and the 

stilling well. Positive values of VHG indicate conditions for 

upward flow (flow from the sediment into the lake), negative values of VHG indicate conditions for downward flow 

(flow from lake into the sediment), and VHG values equal to 

zero indicate the absence of conditions for advective water 

exchange between the lake and the sediment. The VHG value 

does not quantify the amount of flow but provides information about the direction and relative magnitude of flow at each 

location, assuming no change in vertical lakebed hydraulic 

conductivity over the study period.

Uncertainty

The uncertainty in each water-level measurement was 

conservatively assumed to be ±0.02 ft, equal to twice the 

measurement accuracy of the electric tape used for field 

water-level verification measurements and the uncertainty of 

the recording pressure transducers (±0.01 ft). Substituting the 

combined uncertainty of the groundwater (DTWgw) and lake 

water-level (DTWlake) measurements (±0.04 ft) and the length 

depth to the midpoint of the screen (4.42 ft) in equation 2 yield 

a VHG uncertainty of ±0.009 ft/ft. Therefore, VHG values 

between -0.009 ft/ft and 0.009 ft/ft were within the measurement accuracy of the equipment used in this study and cannot 

be confidently determined to be either upward or downward. 

This large band of uncertainty was necessary owing to the 

challenges associated with measuring small head differences 

in a wave-impacted lake system experiencing weather-induced 

barometric pressure fluctuations.

Data Summary

Water-level and calculated VHG data from the 10 study 

sites are presented (figs. 3–13) and summarized (table 2) in 

this section. The amount of data available at each site within 

this period varied depending on the length of equipment 

deployment and transducer performance. Corson-Dosch 

(2020) has complete records of collected continuous waterlevel data, discrete water-level data, and VHG.

Water Levels

Lake water levels at all sites steadily declined during 

the study period. Spring to autumn lake level decline occurs 

annually in UKL and can be attributed to decreased precipitation, irrigation withdrawals (both directly from UKL and from 

tributary rivers), the release of water from the Link River Dam 

downstream to the Klamath River, and increased evapotranspiration– the rates of which are highest during summer 

(Stannard and others, 2013). Groundwater levels in lake-bed 

piezometers also declined over this period and closely tracked 

lake levels. Generally, only small differences were observed 

between lake and sub-lake groundwater levels, averaging 0.03 

ft over the study period.

In addition to the observed seasonal decline in water 

levels, there were frequent but small (approximately 0.1 ft) 

fluctuations in both lake and sub-lake groundwater levels 

that occurred at frequencies of less than 1 day to less than 1 

hour. These fluctuations were probably caused by wave action 

or small seiche events driven by prevailing north to northwest winds. Wind and waves such as these were frequently 

observed. There were also less frequent, large fluctuations 

(approximately 0.25 ft and greater) in the continuous lake 

water-level data. These larger fluctuation events could typically be observed at all sites (for example, large fluctuations 

that occurred on July 25th and August 10th). Because these 

fluctuation events occurred simultaneously at sites across 

the lake, it is unlikely that they are anomalies related to data 

collection. They were probably caused by higher-intensity 

winds or storm events. The larger fluctuation events can also 

be observed in the continuous groundwater-level data all sites, 

though groundwater-level fluctuations generally had smaller 

amplitude than lake-level fluctuations.

Post-deployment continuous water-level records from 

three of the nine piezometers showed recovery curves following the 5 L water slug added for piezometer development immediately after deployment. At LC03 and, to a 

much smaller extent, OC02, post-deployment water levels 

showed slow, decreasing recovery curves from the time-ofdeployment slug to local groundwater conditions. Following 

the time-of-deployment slug, LC03 decreased 2.70 ft over 

4.5 days and OC02 decreased 0.28 ft over 3.5 days. Postdeployment groundwater levels at ON03 also show a slow 

recovery to local conditions but, unlike LC03 and OC02, 

water levels at ON03 increased to local conditions following 
Data Summary 9

Table 2. Continuous data collection and mean vertical hydraulic gradient (VHG) during each week and during the study period at each 

site, Upper Klamath Lake, Oregon, 2017. 

[Available 10-minute VHG data from each week-long period were used to calculate weekly mean values. The bold, colored values exceeded measurement uncertainty (±0.009 foot per foot). The colors indicate gradient direction: positive upward values are blue and negative downward values are red. The colorless values 

were within measurement accuracy and could not be confidently determined to be either upward or downward. No continuous data were recovered from ON01. 

Site locations can be seen in figure 1. Abbreviations: VHG, vertical hydraulic gradient; ft/ft, foot per foot; –, no data available]

Measurement 

period

Weekly mean VHG (ft/ft; unitless)

SPR OS03 ON02 ON03 OC02 LC03 LS01 LC01 LN01

May 2–7, 2017 – 0.0014 – -0.04901 – 0.17682 0.0204 – 0.0067

May 8–14, 2017 – -0.0003 – -0.0090 – 0.0146 0.0245 – 0.0011

May 15–21, 2017 – 0.0019 – 0.0022 – 0.0102 0.0199 – -0.0018

May 22–28, 2017 – 0.0029 – 0.0068 – 0.0106 0.0189 – 0.0080

May 29–June 4, 

2017 – 0.0008 – -0.0086 – 0.0112 0.0186 – 0.0072

June 5–11, 2017 – 0.0020 – -0.0144 – 0.0111 0.0179 – 0.0047

June 12–18, 2017 – 0.0016 – -0.0130 – 0.0086 0.0195 – 0.0043

June 19–25, 2017 – -0.0007 – -0.0036 – 0.0108 0.0173 – 0.0040

June 26–July 2, 

2017 -0.013 -0.0002 -0.0019 0.0037 – 0.0117 0.0113 – 0.0013

July 3–9, 2017 -0.009 0.0019 0.0032 0.0092 – 0.0121 0.0129 0.0033 -0.0017

July 10–16, 2017 -0.017 0.0023 0.0019 – – 0.0108 0.0128 0.0028 0.0090

July 17–23, 2017 -0.028 0.0018 -0.0041 – 0.0077 0.0105 0.0131 0.0041 –

July 24–30, 2017 0.0011 0.0002 -0.0016 – -0.0063 0.0101 0.0114 0.0034 –

July 31–August 6, 

2017 0.0017 0.0013 0.0022 – -0.0111 0.0099 0.0099 0.0019 –

August 7–13, 

2017 -0.0012 -0.0013 0.0047 – -0.0159 0.0106 0.0067 0.0006 –

August 14–20, 

2017 -0.0035 -0.0014 0.0052 – -0.0084 0.0109 0.0081 -0.0001 –

August 21–27, 

2017 -0.0054 -0.0008 -0.0015 – 0.0012 0.0109 0.0074 -0.0007 –

August 28–

September 3, 

2017

-0.0015 -0.0016 – – 0.0079 0.0117 0.0039 0.0106 –

September 4–10, 

2017 0.0008 -0.0038 – – 0.0091 0.0108 0.0007 0.0052 –

September 11–17, 

2017 0.0074 -0.0039 – – 0.0090 0.0085 -0.0006 0.0061 –

September 18–24, 

2017 -0.0103 -0.0050 – – 0.0090 0.0049 -0.0037 – –

September 25–

October 1, 

2017

-0.0005 -0.0048 – – 0.0076 0.0046 -0.0047 – –

October 2–5, 

20173 0.0006 -0.0061 – – 0.0074 – -0.0089 – –

Study period 

mean VHG -0.0052 -0.0005 0.0009 -0.0030 0.0014 0.0102 0.0103 0.0034 0.0039

1Mean VHG value likely influenced by slow recovery of piezometer water levels after installation and is not representative of equilibrium conditions over this 

period. ONO3 study period mean VHG does not include this value.

2Mean VHG value likely influenced by slow recovery of piezometer water levels following screen development slug and is not representative of equilibrium 

conditions over this period. LC03 study period mean VHG does not include this value.

3All equipment removed by October 5, 2017, less than 1 week after measurement began.
10 Benthic vertical hydraulic gradients in Upper Klamath Lake, Oregon, 2017

the time-of-deployment slug test, increasing 0.72 ft over 1.5 

days. It is possible that ON03 was not filled with water during 

the post-deployment piezometer slug and slowly filled with 

groundwater thereafter. Continuous water level records from 

the other six piezometers that had continuous water-level data 

did not show discernable recovery from the post-deployment 

piezometer slug. Because the same installation procedures 

were used to deploy all piezometers, the variation in water 

level recovery time observed among these nine sites indicates 

probable spatial heterogeneity in lakebed sediment hydraulic 

conductivity.

Vertical Hydraulic Gradient

Instantaneous VHG estimates, derived from water levels 

measured at 10-minute intervals, exhibited temporal fluctuations. At all sites, instantaneous VHG values were commonly 

within the range of measurement uncertainty (±0.009 ft/ft) but 

frequently exceeded that range. 63 percent of instantaneous 

measurements were within this range. Instantaneous VHG 

values exceeding the range of uncertainty also changed in 

magnitude with high frequency and often changed direction 

from upward to downward (or downward to upward) on time 

scales ranging from less than 1 day to less than 1 hour. These 

frequent changes in VHG indicate that the rate and direction of 

lake-groundwater exchange at the sediment-water interface are 

dynamic. It is likely that the hourly to daily variability in VHG 

observed across UKL is driven by short-term and often rapid 

changes in lake water level due to wave action or seiches. 

Other studies that have measured exchange flow across the 

sediment-water interface in lakes have documented similar 

high-frequency variability and observed the influence of waves 

and seiches (Schneider and others, 2005; Rosenberry and others, 2013; Naranjo and others, 2019). Rosenberry and others 

(2013) collected high-frequency seepage and VHG measurements at several lakes. They found that seepage rates exhibited 

substantial temporal variability and responded to changes in 

surface-water stage within minutes, and they hypothesized 

seepage rates would be larger during storms. Schneider and 

others (2005) measured groundwater seepage through lakebed 

sediment near the shoreline of Oneida Lake in New York and 

observed considerable variability in seepage rates when wave 

action was severe. Abrupt changes in lake water level from 

wave action or seiche events upset the sediment-lake hydraulic 

equilibrium, inducing instantaneous changes in the direction 

and magnitude of VHG and, therefore, exchange flow and 

enhanced mixing across the lakebed interface.

Mean study period VHG was within measurement uncertainty at seven of the nine sites with continuous water-level 

data, but two near-shore littoral sites (0.0102 ft/ft at LC03 and 

0.0103 ft/ft at LS01) had positive (upward) mean study period 

VHG greater than measurement uncertainty. These sites are 

likely locations of lakebed groundwater seepage.

Instantaneous VHG values were used to calculate mean 

VHG over each week of the study period for which data 

were available (table 2). These weekly mean values provide 

information about the magnitude and variability of site VHG 

over longer (seasonal and weekly) time scales. Overall, 66 

percent of weekly mean VHG values were within the range 

of measurement uncertainty. At the five deeper open-water 

sites (including SPR), 80 percent of the weekly mean VHG 

values (table 2) were within this range, including all weekly 

mean VHG values at OS03 and ON02. 33 percent of weekly 

mean VHG values at SPR, 40 percent at ON03, and 25 percent 

at OC02 exceeded the range of measurement uncertainty–

positive (upward) gradients (VHG greater than 0.009 ft/ft) 

were observed at ON03 and OC02, and negative (downward) 

gradients (VHG less than -0.009 ft/ft) were observed at SPR, 

ON03, and OC02–but most values at these sites were within 

measurement uncertainty. Overall, weekly mean VHG values 

at open-water were variable in both direction and magnitude, 

indicating the occurrence of intermittent hydraulic exchange in 

both directions at these sites over the study period.

Weekly mean VHG values at the four near-shore littoral 

sites were somewhat more consistent in direction and magnitude than those at open-water sites. It is possible that this is 

because the effects of waves and wind were less at the shallower, near-shore littoral sites. All weekly mean VHG values 

at littoral sites that exceeded measurement uncertainty were 

positive (upward flow). Weekly mean VHG values mostly 

exceeded measurement uncertainty at LC03 (82 percent of 

values exceeded range of uncertainty) and LS01 (61 percent 

exceeded) and were predominantly positive (upward flow), 

although weekly mean VHG values at these sites decreased in 

magnitude later in the study period. Values were within measurement uncertainty in September at LC03 and in September 

and October at LS01. Weekly mean VHG values were mostly 

within measurement uncertainty at LN01 (9 percent exceeded) 

and LC01 (9 percent exceeded), but each had one positive 

(upward) value of weekly mean VHG that exceeded measurement uncertainty. Overall, littoral VHG data indicate conditions favorable for consistent groundwater seepage to the lake 

at LC03 and LS01, particularly in the early part of the study 

period, and intermittent minor groundwater seepage at LC01 

and LN01.
Data Summary 11

May June July August September October

2017

2

3

4

5

6

7

8

Depth to water below measuring 

point, in feet 

−0.10

−0.05

0

0.05

0.10

Vertical hydraulic gradient (VHG), 

in feet per feet 

EXPLANATION

EXPLANATION

Upper Klamath Lake—UKL SPR SW

Upper Klamath Lake—UKL SPR GW

Upper Klamath Lake—UKL SPR SW (discrete)

Upper Klamath Lake—UKL SPR GW (discrete)

Vertical hydraulic gradient, 

weekly mean

Vertical hydraulic gradient

Figure 4. Groundwater and lake depth to water below the measuring point and vertical hydraulic gradient (VHG) 

at site SPR in Upper Klamath Lake, Oregon, 2017. [Positive values of VHG indicate upward exchange (sediment to 

lake) and negative values indicate downward exchange (lake to sediment). Site location shown in figure 1]
12 Benthic vertical hydraulic gradients in Upper Klamath Lake, Oregon, 2017

May June July August September October

2017

2

3

4

5

6

7

8

Depth to water below measuring 

point, in feet 

−0.10

−0.05

0

0.05

0.10

Vertical hydraulic gradient (VHG), 

in feet per feet 

EXPLANATION

Upper Klamath Lake—UKL LN01 SW

Upper Klamath Lake—UKL LN01 GW

Upper Klamath Lake—UKL LN01 SW (discrete)

Upper Klamath Lake—UKL LN01 GW (discrete)

EXPLANATION

VHG, weekly mean

VHG

VHG (discrete)

Figure 5. Groundwater and lake depth to water below the measuring point and vertical hydraulic gradient at site 

LN01 in Upper Klamath Lake, Oregon, 2017. [Positive values of VHG indicate upward exchange (sediment to lake) 

and negative values indicate downward exchange (lake to sediment). Site location shown in figure 1]
Data Summary 13

May June July August September October

2017

2

3

4

5

6

7

8

Depth to water below measuring 

point, in feet 

−0.10

−0.05

0

0.05

0.10

Vertical hydraulic gradient (VHG), 

in feet per feet 

EXPLANATION

Upper Klamath Lake—UKL ON02 SW

Upper Klamath Lake—UKL ON02 GW

Upper Klamath Lake—UKL ON02 SW (discrete)

Upper Klamath Lake—UKL ON02 GW (discrete)

EXPLANATION

VHG, weekly mean

VHG

VHG (discrete)

Figure 6. Groundwater and lake depth to water below measuring the point and vertical hydraulic gradient (VHG)

at site ON02 in Upper Klamath Lake, Oregon, 2017. [Positive values of VHG indicate upward exchange (sediment to 

lake) and negative values indicate downward exchange (lake to sediment). Discrete measurements of water level 

and the VHG values calculated using these measurements are identified in the figure explanation. Site location 

shown in figure 1]
14 Benthic vertical hydraulic gradients in Upper Klamath Lake, Oregon, 2017

May June July August September October

2017

2

3

4

5

6

7

8

Depth to water below measuring 

point, in feet 

−0.10

−0.05

0

0.05

0.10

Vertical hydraulic gradient (VHG), 

in feet per feet 

EXPLANATION

Upper Klamath Lake—UKL ON03 SW

Upper Klamath Lake—UKL ON03 GW

Upper Klamath Lake—UKL ON03 SW (discrete)

Upper Klamath Lake—UKL ON03 GW (discrete)

EXPLANATION

VHG, weekly mean

VHG

VHG (discrete)

Figure 7. Groundwater and lake depth to water below the measuring point and vertical hydraulic gradient (VHG) 

at site ON03 in Upper Klamath Lake, Oregon, 2017. [Positive values of VHG indicate upward exchange (sediment to 

lake) and negative values indicate downward exchange (lake to sediment). Discrete measurements of water level 

and the VHG values calculated using these measurements are identified in the figure explanation. Site location 

shown in figure 1]
Data Summary 15

May June July August September October

2017

2

3

4

5

6

7

8

Depth to water below measuring 

point, in feet 

−0.10

−0.05

0

0.05

0.10

Vertical hydraulic gradient (VHG), 

in feet per feet 

EXPLANATION

Upper Klamath Lake—UKL LC01 SW

Upper Klamath Lake—UKL LC01 GW

Upper Klamath Lake—UKL LC01 SW (discrete)

Upper Klamath Lake—UKL LC01 GW (discrete)

EXPLANATION

VHG, weekly mean

VHG

VHG (discrete)

Figure 8. Groundwater and lake depth to water below the measuring point and vertical hydraulic gradient (VHG) 

at site LC01 in Upper Klamath Lake, Oregon, 2017. [Positive values of VHG indicate upward exchange (sediment to 

lake) and negative values indicate downward exchange (lake to sediment). Discrete measurements of water level 

and the VHG values calculated using these measurements are identified in the figure explanation. Site location 

shown in figure 1]
16 Benthic vertical hydraulic gradients in Upper Klamath Lake, Oregon, 2017

May June July August September October

2017

2

3

4

5

6

7

8

Depth to water below measuring 

point, in feet 

−0.10

−0.05

0

0.05

0.10

Vertical hydraulic gradient (VHG), 

in feet per feet 

EXPLANATION

Upper Klamath Lake—UKL LC03 SW

Upper Klamath Lake—UKL LC03 GW

Upper Klamath Lake—UKL LC03 SW (discrete)

Upper Klamath Lake—UKL LC03 GW (discrete)

EXPLANATION

VHG, weekly mean

VHG

Figure 9. Measured groundwater and lake depth to water below the measuring point and vertical hydraulic 

gradient (VHG) at site LC03 in Upper Klamath Lake, Oregon, 2017. [Positive values of VHG indicate upward 

exchange (sediment to lake) and negative values indicate downward exchange (lake to sediment). Site location 

shown in figure 1]
Data Summary 17

May June July August September October

2017

2

3

4

5

6

7

8

Depth to water below measuring 

point, in feet 

−0.10

−0.05

0

0.05

0.10

Vertical hydraulic gradient (VHG), 

in feet per feet 

EXPLANATION

Upper Klamath Lake—UKL OC02 SW

Upper Klamath Lake—UKL OC02 GW

Upper Klamath Lake—UKL OC02 SW (discrete)

Upper Klamath Lake—UKL OC02 GW (discrete)

EXPLANATION

VHG, weekly mean

VHG

Figure 10. Groundwater and lake depth to water below the measuring point and vertical hydraulic gradient 

(VHG) at site OC02 in Upper Klamath Lake, Oregon, 2017. [Positive values of VHG indicate upward exchange 

(sediment to lake) and negative values indicate downward exchange (lake to sediment). Site location shown in 

figure 1]
18 Benthic vertical hydraulic gradients in Upper Klamath Lake, Oregon, 2017

May June July August September October

2017

2

3

4

5

6

7

8

Depth to water below measuring 

point, in feet 

−0.10

−0.05

0

0.05

0.10

Vertical hydraulic gradient (VHG), 

in feet per feet 

EXPLANATION

Upper Klamath Lake—UKL LS01 SW

Upper Klamath Lake—UKL LS01 GW

Upper Klamath Lake—UKL LS01 SW (discrete)

Upper Klamath Lake—UKL LS01 GW (discrete)

EXPLANATION

VHG, weekly mean

VHG

Figure 11. Graph showing groundwater and lake depth to water below the measuring point and vertical 

hydraulic gradient (VHG) at site LS01 in Upper Klamath Lake, Oregon, 2017. [Positive values of VHG indicate 

upward exchange (sediment to lake) and negative values indicate downward exchange (lake to sediment). Site 

location shown in figure 1]
Data Summary 19

May June July August September October

2017

2

3

4

5

6

7

8

Depth to water below measuring 

point, in feet 

−0.10

−0.05

0

0.05

0.10

Vertical hydraulic gradient (VHG), 

in feet per feet 

EXPLANATION

Upper Klamath Lake—UKL OS03 SW

Upper Klamath Lake—UKL OS03 GW

Upper Klamath Lake—UKL OS03 SW (discrete)

Upper Klamath Lake—UKL OS03 GW (discrete)

EXPLANATION

VHG, weekly mean

VHG

Figure 12. Graph showing groundwater and lake depth to water below the measuring point and vertical 

hydraulic gradient (VHG) at site OS03 in Upper Klamath Lake, Oregon, 2017. [Positive values of VHG indicate 

upward exchange (sediment to lake) and negative values indicate downward exchange (lake to sediment). Site 

location shown in figure 1]
20 Benthic vertical hydraulic gradients in Upper Klamath Lake, Oregon, 2017 

May June July August September October

2017

2

3

4

5

6

7

8

Depth to water below measuring 

point, in feet 

−0.10

−0.05

0

0.05

0.10

Vertical hydraulic gradient (VHG), 

in feet per feet 

EXPLANATION

Upper Klamath Lake—UKL ON01 SW (discrete)

Upper Klamath Lake—UKL ON01 GW (discrete)

EXPLANATION

VHG discrete

Figure 13. Graph showing groundwater and lake depth to water below measuring point data and vertical 

hydraulic gradient (VHG) at site ON01 in Upper Klamath Lake, Oregon, 2017. [Positive values of VHG indicate 

upward exchange (sediment to lake) and negative values indicate downward exchange (lake to sediment). No 

continuous data were available at ON01, therefore only discrete measurements of water level and the VHG values 

calculated using these measurements are presented in this study. Site location shown in figure 1]

Conclusion

Groundwater piezometers and lake stilling wells were 

deployed in paired sets at 10 locations in UKL during May–

October 2017. Groundwater and lake levels were monitored 

in the paired piezometers and stilling wells and were used 

to calculate VHGs. Seven of the nine sites with continuous 

water-level data had study period mean VHG with a magnitude equal to or less than measurement uncertainty (±0.009 ft/

ft), owing to the challenges associated with measuring small 

head differences in a wave-impacted lake system. Two nearshore littoral sites (LC03 and LS01) had positive (upward) 

study period mean VHG greater than measurement uncertainty 

and are likely locations of lakebed groundwater seepage. 

Instantaneous VHG data at all sites were highly dynamic and 

exhibited high-frequency changes in magnitude and direction. 

Although most instantaneous VHG values were within measurement uncertainty (VHG within ±0.009 ft/ft), individual 

instantaneous and weekly mean VHG values often exceeded 

this range. Water-level data and VHG estimates summarized 

in this report provide new information about the hydraulic 

conditions at the sediment-water interface in UKL. These 

data demonstrate that sediment-groundwater exchange in 

UKL is temporally dynamic over multiple time scales (hourly, 

daily, seasonally) and spatially heterogeneous. Additionally, 

the observed small rapid fluctuations in VHG, probably due 

to wave effects, may enhance mixing across the sedimentlake interface. Complete water-level and VHG datasets can 

be accessed in the U.S. Geological Survey data release by 

Corson-Dosch (2020).

Acknowledgments

The author gratefully acknowledges Sarah Blocker, 

Marty Erickson, and Justin VonTungeln with the U.S. 

Geological Survey (USGS) Klamath Falls Field Station and 

Adam Gibson and Bradley Smith with the USGS Portland 

Field Office for their considerable help with project field work. 

Jim Kuwabara, Jim Carter, Hedeff Essaid, Francis Parchaso, 

and Brent Topping with the USGS Water Resources Mission 

Area provided equipment and methodological insight that led 

to successful field deployment and data collection. Marshall 

Gannett, Steve Gingerich and Hank Johnson with the USGS 
References Cited 21

Oregon Water Science Center provided thoughtful advice that 

improved this report and data quality. Tiffany Jacklin, Matt 

Johnson and Marc Stewart with the USGS Oregon Water 

Science Center are gratefully acknowledged for their help. The 

Klamath Falls Office of the U.S. Bureau of Reclamation also 

supported this work.

References Cited

Bortleson, G.C., and Fretwell, M.O., 1993, A review of possible causes of nutrient enrichment and decline of endangered 

sucker populations in Upper Klamath Lake, Oregon: U.S. 

Geological Survey Water-Resources Investigations Report 

93–4087, 24 p. [Also available at https://pubs.er.usgs.gov/

publication/wri934087.]

Bureau of Reclamation, 2005, Natural flow of the upper 

Klamath River: Bureau of Reclamation Technical Service 

Center, Denver, Colorado, 77 p. plus attachments.

Cooper, R.M., 2004, Natural flow estimates for streams in the 

Klamath Basin: Oregon Water Resources Department OpenFile Report SW 04-001, 23 p. plus appendixes.

Corson-Dosch, N.T., 2020, Depth-to-water data and calculated vertical hydraulic gradient at the sediment-water 

interface in Upper Klamath Lake, Oregon, 2017: U.S. 

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Publishing support provided by the U.S. Geological Survey

Science Publishing Network, Tacoma Publishing Service Center

For more information concerning the research in this report, contact the

Director, Oregon Water Science Center

U.S. Geological Survey

2130 SW 5th Avenue

Portland, Oregon 97201

https://www.usgs.gov/centers/or-water 
Corson-Dosch—Benthic Vertical Hydraulic Gradients in Upper Klamath Lake, Oregon, 2017—Scientific Investigations Report 2020-5029

ISSN 2328-0328 (online)

https://doi.org/10.3133/sir20205029