Coastal Dunal Landscapes of Western North America

Project Starts March 2002



Dr. Curt Peterson, Professor, Department of Geology, Portland State University

Dr. John Baham, Associate Professor, Department of Crop and Soil Science, Oregon State University

Dr. Trevor Smith, P.E., Professor, Dept. Civil Engineering, Portland State University

Dr. Georg Grathoff, Assistant Prof., Department of Geology, Portland State University

Dr. Errol Stock, Associate Prof., Envir. Sciences, Griffith University, Brisbane, Australia.

Associate Investigators

Roger Hart, Research Associate, College of Ocean and Atmospheric Sciences, Oregon State University

David Percy, Research Associate, Pacific Northwest Geodata, Portland State University





We propose to establish the geohydrologic-, geotechnical-,and hydrogeochemical- properties of stratified dunal deposits in coastal plains that are experiencing a variety of development pressures. During the past few years we have demonstrated that the narrow coastal plains of Oregon, parts of California, and the southern Baja Peninsula, are covered by basal (Pleistocene) dune sheets, deflation deposits, and widespread paleosols (Beckstrand, 2001; Peterson et al., 200x, in prep.). The most-extensive dune sheets, e.g., 3-20 km wide and 30-100 km long (Figure 1) (Cooper, 1958; Dupre et al., 1980, Murillo et al., 1999 ) migrated onshore from the exposed continental shelf during late-Pleistocene periods of marine regression and/or low-stand conditions (24-70+ thousand years ago TLYBP). By comparison, very-small dune advances occurred during the late-Holocene (Orme, 1990; Hart and Peterson, 1997, Hart and Peterson, 200x, submitted). Episodes of dune sheet stabilization, vegetative colonization, and surface leaching produced low-permeability paleosols that stratify the dune deposits (Figure 2a). Secondary mineral precipitation from groundwater flow along paleosol redox-boundaries further cemented these critically-important horizons. The hydrologic- and geotechnical- properties of the paleosols are largely responsible for the ‘anomalous’ groundwater flow and ‘unpredictable’ slope stability in the dune sheets that mantle the coastal plain.

Many land-use conflicts are associated with the stratified nature of the underlying dune sheets. For example, governmental regulation and private-property rights clash when paleosol-aquitards temporarily hold-up or drain ‘ephemeral’ wetlands (Figure2d)(Shultz, 1998). Septic systems, sensitive lakes, and drinking water aquifers can be linked or isolated by subsurface paleosol-aquicludes.

The relative mobility of iron, calcium, silica and associated trace elements imprint the dunal groundwater chemistry, thereby limiting water-resource management strategies (Bortleson et. al., 1989). For example, Fe-hydroxide precipitation has resulted from the mixing of Fe-rich dunal groundwater with oxygenated lake water, thereby smothering lake epifuna. Dissolved Fe-is particularly elevated in the basal layers of the dunal aquifers.

The stratified dunal deposits also create geotechnical difficulties. Road cuts and engineered embankments that are cut into stratified dune deposits, i.e., buttressed by the cemented paleosols, appear to be stable during construction then slump during the next rainy season (Figure 2c). Weakly-cemented dunal deposits resting on over-steep sea-cliffs stand for decades then fail catastrophically (Figure 2d).

We have initiated the first regional compilation of coastal dune-sheet extent and age of emplacement in Western North America (Sea Grant 2000-2002) since Cooper’s pioneering work a half century ago (1958, 1967). Relatively new technologies of thermal luminescence dating (TL) ground penetrating radar (GPR), and interactive WEB-based GIS have revolutionized the study of these coastal landscapes. With Tri-State and international cooperation (see Collaborators) we are nearing completion of paleosol reconnaissance mapping (over 300 sites) and age dating (40 sites) of the major dune sheets in southwest Washington, Oregon, northern California, and Baja California South ( Grant/). Our dating of west-coast dune-sheet advances is being coordinated with ‘Early Coastal Site’ archaeology studies by Erlandson et al., (FERCO, NSF 1998-2001) and Hall et al., (Sea Grant 2000-2003).

At the regional scale of paleodunal mapping (yr 1996-2000) we did not address the hydrogeology-related questions of paleosol orientation, continuity, and geometry in the subsurface (see Objective 1). Our field mapping has demonstrated wide ranges in dunal soil-strengths (0.5-4.5 kg/ 1a), as have previous reports (Schlicker et al., 1973; Table 1b). However, the crucial determinations of ‘drained versus undrained’ failure conditions, and associated ASTM soil tests of the interlayered paleosols, are unknown (see Objective 2).

We have performed preliminary mineralogical analyses of the paleosol clays and dune-strata cements (Table 2a) (Grathoff et al., 2001), and others have found high concentrations of dissolved species in the groundwater (Table 2b). By comparison, relatively little is known about specific redox potentials and solubility equilibria of the stratified dunal-aquifer system (see Objective 3).

We are educating the coastal communities and planners about the extent and nature of the coastal dunal landscape (see Project Management and Outreach). We must

TABLE 1 Part A:

West Coast Dune and Paleosol Penetrometer-Data (kg/sqcm)

Dune Strata Paleosol Horizons

Max (3.5-4.5) Max (>4.5)

Mean (1.0-2.0) Mean (2.5-3.5)

Min. (0.0-0.5 Min. (0.5-1.5)

Sea Grant 2000-2001 Field Sampling: Oregon, California, B.C.S

Part B:

*Geotechnical Data from Oregon Coastal Plain

Parameter Stabilized Dunes Stratified Dune/Terrace Paleosols

Soil Type SM ML

Sieve/Hydrometer 99sand/1silt/0clay 30-95sand/5-35silt/0-25clay

Internal Friction 32-37 14-38

Cohesion 0 4-7

Liquid Limit 20-33 15-25

Plasticity 0 0-4

Schlicker et al., 1973

TABLE 2 Part A

Identified Soil Mineralogy Techniques used for identification

Fe-Vermiculite-Chlorite/Smectite X-ray Diffraction (14.2->14.4 Å on Glyc)

Kaolinite Al2Si2O5(OH)4 X-ray Diffraction (7.1 Å)

Gibbsite Al(OH)3 X-ray Diffraction, M-probe (4.86, 4.37 Å)

Allophane Al1-2Si1Ox X-ray Diffraction, SEM, EDX (2.25, 3.3 Å)

Fe hydroxides/oxides Fe(OH)X Differential X-ray Diffraction

Calcite Ca(CO)3 X-ray Diffraction, SEM, EDX

*Paleosol/Cement Mineralogy from Grathoff et al., (2001)

Part B

Dunal Groundwater Chemistry (Florence/Coos Dune Sheets) All Data in mg/L

Fe (0.01-46) Ca (0.44-50) Mg (0.8-32) Mn (0.05-0.19) Al (0.03-0.17)

Na (6.8-480) K (1.1-43) Cl (8.6-590) SO4 (1.2-49)

*Compiled from Dobberpuhl et al., (1985), Bortleson et al., (1989; 1992)

** High Na, Cl, from basal saltwater layers. Sources of high Fe, and some other metals, are not well constrained but, might reflect solid-phase dissolution under reducing conditions from microbial decomposition of organic-C (see Objective 3).

also communicate directly with the professional specialists, e.g., city engineers, consulting hydrologists, and registered geologists, about the unique properties of the stratified dunal deposits (see Objective 4).


Our goal is to conduct the first fully-integrated study of paleosol-aquitard distribution, slope stability, and groundwater redox-chemistry in stratified dunes of the coastal plain using combined technologies of ground penetrating radar, in-situ and lab geotechnical testing, and groundwater geochemical analysis. To reach this goal we propose the following objectives.

OBJECTIVE (1) To establish paleosol geometry, continuity, and overlap relations we will use ground penetrating radar (GPR) and ground-truthing by auger/drilling to map paleosols in the shallow subsurface (5-20 m depth) in near-coast deflation flats and foothill dune ramps (Figure 3) (see Methods). Groundwater level, i.e., total head and gradient, will be simultaneously mapped with the GPR to establish potential paleosol relations with perched-water tables, ephemeral wetlands, and sensitive ponds in the dune sheets. We will test two hypotheses of paleosol distribution: (1) Relatively continuous, but flat and thin, Bg/Bw paleosols are vertically-stacked (seaward) in deflation flats (0-50 m elevation), (2) Discontinuous, but thick and undular Bt soils, are developed (landward) in parabolic dune-ramps against the foothills (50-120 m elevation). We will use orthagonal GPR traverses (leveling by EDM-total station) to test paleosol continuity, concavity, and overlapping relations, which are of critical importance to confining groundwater flow (see Methods).

OBJECTIVE (2) To characterize the paleodunal geohydrologic- and geotechnical-properties of dune sand strata and intervening paleosols we will perform a variety of standardized ASTM in-situ and lab-based tests. Specifically, hydraulic conductivity (permeability) of exposed dunal strata and paleosol horizons will be measured insitu using standard constant-head /falling-head tests (Fetter, 1994). ‘Undisturbed’ samples from the exposed field strata will be taken to the lab for measurements of hydraulic conductivity, and wet- and dry- bulk density, yielding void ratio, i.e., porosity (Figure 3b). Several shallow observation wells will be installed and tested for hydraulic conductivity and paleosol vertical transmissivity by Open-End tests. These hydrologic tests have not previously been performed at the scales of discrete paleosols, i.e., 05-100 cm in thickness.

The most important criteria for establishing dunal soil strength are (1) identifying which units initiate the slope failures, and (2) whether slope failures occur in drained (granular dune sand) or undrained (clayey-silty paleosol) conditions. We will identify the ‘critical’ failure horizons by direct field-observations (winter 2002-2003) and by standard ASTM tests (see Methods)(Das, 1994). The local seepage conditions set the effective stresses in the soil mass and dictate strengths under both drained and undrained conditions. We will establish the range of saturated critical strengths from both insitu ASTM tests (vane, penetrometer, SPT and pressure meters) and lab-based ASTM tests (drained and undrained direct shear) on loose, and cemented dune strata (Smith and Rollins, 1997). Tests will be made in exposed roadcuts, eroding sea-cliffs, and in adjacent subsurface bore-holes (see Methods).

OBJECTIVE (3) To characterize the hydrogeochemical properties of the stratified dunal deposits we will analyze groundwater chemistry and associated cementing minerals. The distribution of dissolved elements (Fe, Al, Ca, and Si, among others) and their precipitation as cements/clays result from ‘natural’ soil forming processes along the coast (Langley-Turnbaugh and Bockheim, 1997). However, ‘land-use’ changes can also impact the groundwater chemistry in the coastal dunes. The concentration of dissolved Fe in shallow groundwater in an Oregon dunal aquifer has increased form a median value of less than 100 ug/L in 1956 to a values as large as 27,000 ug/L in 1989 after the area was planted to dense forest (Bortleson et al,. 1989).

Dunal soil solutions and shallow groundwater samples will be collected from strata actively involved in the formation of Fe, Mn, Si, and Al cemented horizons with low water permeability (see Objective 2). The mobilization of these cementing agents is likely the result of anaerobic mineralization of organic matter deposited in the near surface of the soil and the migration of Fe, Mn, and Al in organically-complexed soluble forms (Bortleson et al., 1989; Baham et al., 200xa, in prep.). We will compare the dissolved and solid phase elemental species on a seasonal basis with insitu pH and redox conditions (see Methods). We will use standard groundwater dating methods, i.e., Tritium (Loosli et al., 1998) to constrain recharge and residence time in the shallow aquifer strata (see Methods). We will also use new Fe-isotope ‘biosignature’ methods (Anbar, 2001, Brantley et al., 2001) to establish the biogeochemical conditioning of water in the dunal aquifers (see Methods).

OBJECTIVE (4) To directly communicate our major findings to the coastal civil engineers, hydrologists, and registered geologists we will present our study results (1) at professional-specialist meetings (GSA, AEG, ACE), (2) in peer-reviewed papers submitted to appropriate ‘professional’ journals, and (3) on our ‘Coastal Dunal Landscape’ Web-pages. The study team will work with Sea Grant Extension personnel to organize 3-4 coastal field trip/meetings with coastal city engineers and county planners

during the second year of the study (2004) to demonstrate direct applications of the study findings (see Project Management and Outreach for details of Objective 4).


Ground Penetrating Radar Surveys:

This project will establish the first dedicated coastal ground-penetrating-radar (GPR) facility on the west coast to be shared by Universities and agencies in Oregon, Washington and California. We will purchase a multi-frequency GPR system, such as the Sensors& Software PulseEKKO100A 50,100, 200 Hz system with 1000V Pulser for deeper penetration. We have used GPR extensively in coastal Washington and northernmost Oregon, with study collaborator Jol, to map beach-retreat scarps, dunal paleosols, and groundwater levels in foredune-ridge plains (Meyers et al., 1996, Jol et al., 1995, 1999; Fiedorowich and Peterson, 2001). Jol is currently working with these authors in GPR mapping of archaeological sites in coastal dunal paleosols this summer (Sea Grant 2001) and will assist us in the set-up of the west coast Coastal-GRP facility.

As discussed in Objective 1 the GRP will be used extensively to map paleosols, groundwater levels, water-table gradients, and the seasonal variation of perched water-table levels in the coastal dune aquifers. We will start with existing GPR surveys (>10 km of trackline) from the foredune-ridge plains of southwest Washington (Peterson et. al., 2000). New GPR surveys (5-10 km trackline each) will be performed in representative field sites including (1) basal Pleistocene dune sheets, and (2) steeply-sloping parabolic dune-ramps in Oregon (Figure 4). Subsurface ground-truthing of the GPR ‘paleosol’ reflectors and groundwater levels will be performed with sand auger/drilling.

Geotechnical Testing:

Preliminary site assessment for civil works, development or excavation for highways begins with the preliminary site investigation, including the Standard Penetration Test (SPT) blow count. In accepted geotechnical practice each project then has more detailed exploration(s) that typically include more sophisticated sampling and testing from the soil types identified (Table 3).

Table 3: Geotechnical Testing

For the Laboratory analysis proposed tests are:

Grain size distribution by sieve and hydrometer (ASTM D422)

Liquid and Plastic Atterberg Limits (ASTM D4318)

Direct Shear (ASTM D3080) for both drained and undrained shear strength testing

Constant Head Permeability test (ASTM D2434)

Unconfined Compression (ASTM D2166)

For the field identification and testing both preliminary characterization tests and insitu tests are proposed including:

Miniature Vane (ASTM D 2573)

Cone Penetrometer

Pressuremeter (ASTMD4719-87)

Standard Penetration Test (ASTM D1586)

Pocket Penetrometer


Sand Cone Density Test (ASTM D1556)

Of most concern to the design community is whether or not these deposits exhibit undrained, short term, behavior as well as the long term, drained behavior. We propose to test four representative sites (Figure 4) with alternative dune strata and cemented paleosols to provide a range of unit weights, permeabilties and shear strengths. Fieldwork includes the SPT and Pressuremeter (PMT) testing for identification of drained and undrained behavior in mud rotary or auger holes. The PMT is a hydraulically operated down-borehole stress strain device designed to measure soil stiffness and shear strength (Figure 3c). It represents one of the most high-quality insitu tests in geotechnical design, providing soil-stength data comparable to the triaxial test, but under true insitu conditions (Smith et. al., 1991a,b; 1995). The Civil Engineering Department at PSU has 4 different PMT probes and 3 control units, being the only university in the western US operating such devices. Cohesive soils will have unconfined strength tested by vane and penetrometer tests and samples will be retrieved in bags and thin walled Shelby tubes (ASTM D1587) for laboratory evaluation. We will use a combination of drill-rigs for the geotechnical testing, including a mud-rotary rig that is co-operated by the Civil Engineering Departments of Oregon State University and Portland State University.

Groundwater Chemistry:

One well transect (2-3 wells) will be placed in a foredune-ridge plain (Long Beach, WA). We will place 1-2 well transects in Pleistocene dunal deflation-plains (Newport and Bandon dune sheets, OR) where gradients in vegetation density exist (Figure 4). We also will place 1-2 well transects on sloping dune-ramps (Florence/Coos Bay dune sheets, OR) where they meet the foothills of the coast range. These wells will be located adjacent to the geotechnical boreholes, and nearby GPR traverses (see Objectives 1 and 2). The shallow wells (about 35 in number) will be auger-drilled and installed with airtight, 5 cm-diameter PVC pipe, and screened with fine glass-sand immediately above the shallowest-paleosol aquitard. Additional dunal sea-cliff springs (3-4 in number from southern Oregon and northern California) will be sampled to give a range of dunal water-qualities associated with the paleosol aquitards.

Shallow Water Samples

Wells will be installed just above the low-permeability hydroxide/clay-cemented (paleosol) horizon(s) within several meters depth. We expect the origin of the high-Fe groundwater to be near the vegetated surface where the decomposition of organic-carbon drives reductive dissolution (Figures 5a,b). Each shallow-well will be equipped with an internal Pt electrode for redox measurement. Well water samples will be taken with a hand pump; under argon or nitrogen as the sample is withdrawn. Purging the well casing with inert gas prevents the oxidation of Fe/Mn, and co-precipitation of P. It also allows for a reliable measurement of dissolved O2 on-site (Baham et al., 200xb, in prep.). The samples will be immediately filtered through glass fiber into plastic bottles with acid to slow Fe/Mn reduction. Unfiltered, unacidified samples will also be collected for the measurement of DIC, pH, and EC.

A series of three to four ‘deeper-well’ experiments will be conducted in which highly-vertically-resolved pore water samples will be collected within and between vertically-stacked paleosols. A specially designed diffusion-chamber sampler (Peeper) equipped with a Pt electrode in each of the diffusion cells (Baham et al., 1999) will be used to sample discrete groundwater horizons. After a 14-day equilibrium period, the redox potentials of each of the cells will be measured, and then pore water from each of cells will be removed with a syringe by piercing the cell membrane.

Chemical Analysis of Soil Pore and Shallow Ground Water

Shallow-well samples and water samples collected with the pore water diffusion chambers (Peepers) will be analyzed for a suite of elements within two days of sample collection. Total soluble concentrations of Fe, Al, Mn, Si, Ca, Mg, K, Na, and P will be determined by ICP-atomic emission spectroscopy at Oregon State University. Dissolved organic and inorganic carbon will be measured with an IR detector after chemical oxidation. pH will be determined potentiometrically. Sulfate, F, and, Cl will be determined by ion chromatography. Ammonium, NO3, Fe(II), and PO4 will be determined colorimetrically. Electrical conductivity will be measured and used to estimate the total ionic strength of the solution. MINEQL+ will be used to model the aqueous equilibria and to test hypothesis regarding the formation and stability of possible mineral cementing agents (Baham et al., 1999). The mineral precipitates from corresponding depths in auger holes will be analyzed for the total amounts of amorphous and crystalline Fe, Mn, Si, and Al cementing agents (Microprobe) as well as diagenetic clays (XRD and differential XRD after Fe-dissolution) present in the restrictive layers.

Several of the well transects will be sampled for groundwater dating and Fe isotopic signatures. One liter samples will be collected for bomb-blast Tritium tracers (post-1960’s). If the samples are ‘old’ then C14 or other methods may be required to establish groundwater ages. Well water and amorphous Fe-cements will be sampled for 56Fe/54Fe ratios, to be analyzed with a new multicollector-ICP-MS at Oregon State University. We will test whether the isotopic signature(s) reflect biological reduction of the Fe-mineral phases (Wiederhold et al.,200x, in prep.) in the upper dunal layers. The Tritium and Fe-isotope ‘tracers’ should reflect groundwater recharge rates, residence times, and links to surface land-use.


First Year (March 2002) (Feb. 2003)

Field-investigation of dunal-slope failures

Selection of GPR traverses, geotechnical-sites, and shallow water-well transects

Geotechnical testing of dunal soil strengths (field and lab)

GSA session and field trip on coastal paleodunal landscapes

Summer GPR surveys of paleosol geometry and water-table levels (OR)

Installation of shallow water wells (WA/OR)

Winter groundwater-sampling and lab analysis

Develop and Post ‘Geotechnical’ Web-pages

Second Year (March 2003) (Feb. 2004)

Preparation for presentations at AEG, ASCE meetings

Winter GPR surveys of water-table levels and gradients

Spring/summer groundwater-sampling and lab analysis

Manuscript preparation: ‘Dunal Geotechnical pProperties’

Summer GPR surveys of paleosol geometry and water-table levels

Manuscript preparation: ‘GPR Survey of Paleosols/Water-Tables’

Develop and Post ‘Hydrogeochemistry’ Web-pages

Conduct coastal-professional workshops/field trips

Manuscript preparation: ‘Hydrogeochemistry’


We anticipate 3 major outcomes from this proposed research. (1) We will establish over what length-scales (100’s meters to multi-kilometers) the shallow-subsurface paleosols serve as effective aquitards in the dunal aquifers. These results will have direct and immediate application to wetland regulation, large-scale development planning, and groundwater flow-modeling in the coastal plain. (2) We will establish to what extent the cemented-paleosols serve as critical failure horizons in dunal sea-cliffs, roadcuts, and engineered slopes in the coastal plain. These results will establish the ‘Standard of Practice’ for geotechnical engineering design in the stratified dunal deposits, and serve notice to planners and developers regarding potential slope instabilities. (3) We will identify the source of high-dissolved Fe, and other associated ions, in the dunal aquifer, and relate the aquifer water-quality to surface conditions of vegetation, septic system loading, and drainage. The results of this study will be used by cities, water boards, and state agencies, to develop water-resource management options that are consistent with the hydrogeochemistry of the dunal aquifers.


This proposal represents an ambitious effort to study and disseminate findings on the inter-related properties (hydrogeologic, geotechnical, and hydrogeochemical) of stratified dunal-deposits in the coastal plain. The nature of this effort is highly interdisciplinary (geology, hydrology, hydrochemistry, and civil engineering). These investigators have been working together on west coast dune problems since 1996. Peterson will be on sabbatical during the 2003-2004 academic year, and will devote this time to coordinating the field and lab work. Study analyses and results will be posted promptly on the project Web-site ( Grant/) enabling rapid dialogue among investigators, students, and collaborators. The interactive Web-pages will also provide online references to busy professionals, and engage the interested public in the ongoing coastal research, as monitored by Web-page ‘hits’.

Because our target users are ‘professional’ specialists, it is important that we produce peer-reviewed, i.e.,‘peer-accepted’ publications, which they can reference for design practice standards. We will publish three major works on (1) GPR mapping of paleosol aquitards, (2) geotechnical characertization of mixed (drained and undrained) dunal strata to ASTM standards, and (3) redox-geochemical conditioning of dunal-aquifer groundwater (see Objective 4). Our broad base of study collaborators and representation on State geotechnical and coastal-hazard task forces (Smith and Peterson) will ensure that the study findings are incorporated into State- and federal-agency planning. The most direct outreach-efforts proposed here are the project’s coastal city/county staff workshops scheduled for 2003-2004 (see Objective 4). These will be onsite and infield workshops designed to guide planners and engineers in using the study findings for their planning, site-investigations, and permitting duties. Post-workshop evaluations will be solicited and reviewed by the study team and Sea Grant Extension for follow-up activities.


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