Geomorphic Mapping of the Chehalis River Floodplain, Cosmopolis to Pe Ell, Grays Harbor, Thurston, and Lewis Counties, Washington

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GEOMORPHIC MAPPING OF THE CHEHALIS RIVER FLOODPLAIN, COSMOPOLIS TO PE ELL, GRAYS HARBOR, THURSTON, AND LEWIS COUNTIES, WASHINGTON

by Stephen L. Slaughter and Ian J. Hubert

WASHINGTON DIVISION OF GEOLOGY AND EARTH RESOURCES Information Circular 118 July 2014

DISCLAIMER Neither the State of Washington, nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the State of Washington or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the State of Washington or any agency thereof. This map product has undergone a high level of internal agency review by geologists, cartographers, and editors.

WASHINGTON STATE DEPARTMENT OF NATURAL RESOURCES Peter Goldmark—Commissioner of Public Lands

DIVISION OF GEOLOGY AND EARTH RESOURCES David K. Norman—State Geologist John P. Bromley—Assistant State Geologist

Washington Department of Natural Resources Division of Geology and Earth Resources Mailing Address: Street Address: MS 47007 Natural Resources Bldg, Rm 148 Olympia, WA 98504-7007 1111 Washington St SE Olympia, WA 98501 Phone: 360-902-1450; Fax: 360-902-1785 E-mail: [email protected] Website: http://www.dnr.wa.gov/geology

Publications List: http://www.dnr.wa.gov/ResearchScience/Topics/GeologyPublications Library/Pages/pubs.aspx

Washington Geology Library Catalog: http://www.dnr.wa.gov/ResearchScience/Topics/GeologyPublications Library/Pages/washbib.aspx

Washington State Geologic Information Portal: http://www.dnr.wa.gov/portal

Suggested Citation: Slaughter, S. L.; Hubert, I. J., 2014, Geomorphic Mapping of the Chehalis River Floodplain, Cosmopolis to Pe Ell, Grays Harbor, Thurston, and Lewis Counties, Washington: Washington Division of Geology and Earth Resources Information Circular 118, 59 p. map book, scale 1:28,000 and 2 p. text.

© 2014 Washington Division of Geology and Earth Resources Published in the United States of America Geomorphic Mapping of the Chehalis River Floodplain, Cosmopolis to Pe Ell, Grays Harbor, Thurston, and Lewis Counties, Washington by Stephen L. Slaughter and Ian J. Hubert Washington Division of Geology and Earth Resources MS 47007; Olympia, WA 98504-7007

SUMMARY This map book is a visualization tool intended to assist in identification of geomorphic and anthropogenic landforms in the approximate Chehalis River 100-year floodplain. The map book delineates subtle landforms on the floodplain for a 110-mile reach of the Chehalis River between Pe Ell and Cosmopolis, Washington. The intended users of the map book include biologists, wetland scientists, land managers, property owners, geologists, botanists, floodplain managers, watershed managers, and those interested in the subtle geomorphic features of the Chehalis River floodplain. All landforms were interpreted from remote analysis of lidar and aerial imagery and no field validation was performed for any portion of this project. Note that this is not a flood prediction or flood depth map and cannot be used as such; it is only intended as a visualization tool for the geomorphology of the Chehalis River floodplain.

DESCRIPTION Data was interpreted by a geologist using a geographic information system (GIS) to analyze a relative elevation model derived from 1- and 2-meter lidar digital elevation models (DEMs) and 12-inch-resolution aerial images from 2011. These maps are relative elevation models (REMs) that represent the elevation of features on a floodplain relative to the Chehalis River’s water surface by removing downstream changes in elevation associated with the channel gradient, a process termed ‘detrending’ (Wash. Dept. of Ecology, unpublished documents, 2013). Essentially, the elevation of the river between Pe Ell and Cosmopolis was adjusted to 0 feet, and the elevation of the features adjacent to the river were also reduced by a similar elevation. This visualization method reveals subtle changes in floodplain elevation, specifically geomorphic features within the floodplain, such as abandoned channels, ditches, stream channels, roads, and other natural and anthropogenic features. In this map book, features include lines that delineate primary channels, secondary channels, sloughs, swales, elevated grades, natural levees, and artificial levees. The final three mapped landforms (elevated grades, natural levees, and artificial levees) are raised features on the floodplain that exceed approximately 1-foot elevation above the adjacent floodplain. Primary and secondary channels, slough, and swale landforms are incised features or depressions in the floodplain that exceed approximately 1-foot elevation below the adjacent floodplain.

DEFINITIONS OF THE GEOMORPHIC LANDFORMS Because this project was limited to reconnaissance mapping techniques, there was no detailed field validation of landforms. Therefore, we used broad landform categories to encapsulate geomorphic and anthropogenic features. For instance, any raised and elongate feature with an elevation approximately 1 foot above the floodplain (both modern and abandoned) and not used as a transportation network (paved road, gravel road, railroad line, etc.) is categorized as an ‘artificial levee’. There may be cases where poor lidar returns will show dense, stream-adjacent brush as an elevated feature that resembles an artificial levee, and the feature will likely be mapped as such. These are considered acceptable errors for reconnaissance mapping. Below are descriptions of the landforms identified on the floodplain and other terms used in this report.

• Cut-off. An abandoned meander bend that has been short-circuited by the river flow. Cut-offs become infilled over time by a process of abandoned-channel accretion. For these maps, the terms ‘cut-off’ and ‘oxbow lake’ may be used interchangeably due to difficulties in observing surface water in aerial imagery. • Ditch. An artificial, typically linear excavation used to aid in drainage and movement of surface water. Ditches are typically linear whereas natural stream channels are sinuous; however, there may be occasions where the two are difficult to discern and so the terms may be used interchangeably. • Flood channel. A channel that bypasses the main channel during flooding. Flood channels are typically relatively straight, have a lesser depth than the main channel, and remain dry for much of the year, only becoming filled with water as flow approaches bankfull or channel capacity. • Grade, elevated. Any transportation network constructed on fill above the floodplain, including highways, secondary roads, gravel roads, railroads, etc. They can be either in use or abandoned. Road beds must be elevated at least 1 foot above the adjacent floodplain to be included. • Levee, artificial. Any linear feature constructed above the floodplain that does not act as a transportation network (see Grade, elevated). Artificial levees are typically broad at the base and taper with height. These elongate features may be several miles long or very short and simply encircle a structure in the floodplain. Levees may be used for flood defense to increase channel capacity at high flows • Levee, natural. An elongated, raised ridge formed at the channel–floodplain boundary during overbank flow. The height of a levee is scaled to the size of the channel, and its presence implies a relatively stable channel location. Note that what appears to be a levee on the lidar may actually be dense vegetation impenetrable to lidar. This is particularly likely in Thurston County, where bare-earth lidar returns are very poor in places with tree canopy because the lidar was collected during deciduous leaf-on conditions. • Lidar. An acronym for Light Detection and Ranging, a remote-sensing method that uses light from a pulsed laser to measure the distance to the Earth’s surface. When combined with other data recorded by the airborne system, it can generate precise, three-dimensional information about the ground surface. • Meander scroll bar. A former point-bar deposit that now appears as ridge-and-swale topography at the location of the former point bar. • Oxbow lake. A lake, typically U-shaped, formed by an abandoned meander bend (cut-off). For these maps, the terms ‘cut-off’ and ‘oxbow lake’ may be used interchangeably due to difficulties in observing surface water in aerial imagery. • Paleochannel.A longer section of an abandoned channel that may exhibit a wide range of different shapes on the map. Paleochannels gradually become infilled by abandoned-channel accretion; the degree of infilling reflecting the age of the channel. The rate of infilling is dependent on factors such as the geometry of the paleochannel and its position on the floodplain in relation to overbank deposits. • Primary channel. The Chehalis River channel from Pe Ell to Cosmopolis, delineated using lidar bare-earth hillshades. • Secondary channel. Any stream channel or ditch that could transport surface water to the Chehalis River. • Slough. A seasonally inundated, active channel or floodplain depression typically not connected with the primary channel at low flow, including oxbow lakes and flood channels. • Stream channel. Any secondary stream that flows into the Chehalis River. Ditches are typically linear whereas natural stream channels are sinuous; however, there may be occasions where the two are difficult to discern and so the terms may be used interchangeably. • Swale. An active channel or floodplain depression that is disconnected from the primary channel at low flows, but inundated at highest flows. This landform includes cut-offs, meander scroll bars, and paleochannels. Map Index. Area of geomorphic mapping of the Chehalis River floodplain between Pe Ell and Cosmopolis showing relative elevation and areas of detailed figures (black boxes) in the following map book. Two types of maps are provided for each numbered map area: the first map contains interpreted geomorphic features; the second map shows the relative elevation model. If viewing digitally, click the numbered yellow boxes on the inset map (above) to navigate to the corresponding Map Sheets in the map book. The link provided on the top of each map book page navigates back to the Map Index. Click here to return to map index

Geomorphic Features - Map Sheet no. 1

123'49'W 123' 48'W 123' 47'W

River s hali Che

123'49'W 123'48'W 123' 47'W

N 0 0.5 1 mile A Click here to return to map index

Relative Elevation Model - Map Sheet no. 1

46"59'N

46"58'N

46"S8'N

46"57'N

N 0 0.5 1 mile A Click here to return to map index

Geomorphic Features - Map Sheet no. 2

123"46'W 123"45'W 123"44'W

46°59'N

46"59'N

46' 58.N

46' 58'N

River s hali Che

46' 57'N

123'46'W 123' 45'W 123' 44'W

N 0 0.5 1 mile A Click here to return to map index

Relative Elevation Model - Map Sheet no. 2

123°46W 123"45W 123"44W

123' 46W 123' 45W

N 0 0.5 1 mile A Click here to return to map index

Geomorphic Features - Map Sheet no. 3

123•43w 123'42'W 123'41'W

46'SS'N

ver Ri Chehalis

46' 57'N

46'57'N

46°56'N

46'56'N

123°43'W 123°42'W 123'41'W

N 0 0.5 1 mile A Click here to return to map index

Relative Elevation Model - Map Sheet no. 3

123"43W 123"42W 123"41W

46"58'N

46' 58'N

46' 57'N

46•S7'N

46*56'N

N 0 0.5 1 mile A Click here to return to map index

Geomorphic Features - Map Sheet no. 4

123'40'W 123'39'W 123'oSW

46'59'N

46' 58'N

46'58'N

46' 57'N r e v 46' 57'N C i h R eha lis

123' 40W 123' 39W 123' 36'W

N 0 0.5 1 mile A Click here to return to map index

Relative Elevation Model - Map Sheet no. 4

123' 40W 123' 39W 123' :laW

46' 59'N

46'58'N

46*57'N

123' 40W 123' 39W 123':laW

N 0 0.5 1 mile A Click here to return to map index

Geomorphic Features - Map Sheet no. 5

123"37W 123'36W 123'35W

46'59'N

r 46' S8'N e i v R 46' S8'N

is al h e h C

46'57'N

123' 37W 123'36W 123' 35W

N 0 0.5 1 mile A Click here to return to map index

Relative Elevation Model - Map Sheet no. 5

123"37W 123'36W 123' 35W

46'59'N

46' 59'N

46'58'N

46•S8'N

46' 57'N

123' 37W 123' 36W 123' 35W

N 0 0.5 1 mile A Click here to return to map index

Geomorphic Features - Map Sheet no. 6

123'34'W 123'33'W 123'32'W

47°0'N

46'S9'N

46'5S'N C heh al is River

123' 34'W 123'33'W 123'32'W 123'31'W

N 0 0.5 1 mile A Click here to return to map index

Relative Elevation Model - Map Sheet no. 6

123"34W 123"33W 123"32W

123' 34W 123' 33W 123' 32'W 123' 31W

N 0 0.5 1 mile A Click here to return to map index

Geomorphic Features - Map Sheet no. 7

123' 31'W 123' 30'W 123"29'W

r ve Ri

alis Cheh

123' 31'W 123'30'W 123' 29'W 123'28'W

N 0 0.5 1 mile A Click here to return to map index

Relative Elevation Model - Map Sheet no. 7

123"31W 123"30W 123"29W

47"0'N

46' 59'N

46"59'N

46'58'N

46' 58'N

123"31W 123' 30W 123' 29"W 123' 28W

N 0 0.5 1 mile A Click here to return to map index

Geomorphic Features - Map Sheet no. 8

123' 28'W 123'27W 123'26'W

47° 1'N

47' 0'N

46' 59'N

River

Ch eh alis

123'28W 123'27'W 123'26W

N 0 0.5 1 mile A Click here to return to map index

Relative Elevation Model - Map Sheet no. 8

123' 28'W 123'27'W 123' 26'W

123' 28'W 123' 27'W 123' 26'W

N 0 0.5 1 mile A Click here to return to map index

Geomorphic Features - Map Sheet no. 9

123' 25'W 123' 24W 123'23'W

47'0'N

lis ha he C

46' 59'N

Riv er

46' S8'N

123' 25W 123' 24W 123' 23W

N 0 0.5 1 mile A Click here to return to map index

Relative Elevation Model - Map Sheet no. 9

123' 25W 123'24W 123' 23W _,

47'0'N

46' 59'N

46'58'N

123' 25W 123' 24W 123' 23W

N 0 0.5 1 mile A Click here to return to map index

Geomorphic Features - Map Sheet no. 10

123•22w 123•21w 123·2QW

46' 59'N

Ch ehalis 46' 5a'N

R iv er

46'57'N 123'22'W 123' 21'W 123' 20'W

N 0 0.5 1 mile A Click here to return to map index

Relative Elevation Model - Map Sheet no. 10

123' 22'W 123' 21W 123' 20W

46' 59'N

46' S9'N

46' S8'N

46' 58'N

46'S7'N

46'57'N 123' 22W t 23' 21W 123"20W

N 0 0.5 1 mile A Click here to return to map index N srN · r56"N ·•ss · "t6W 23 1 1sw • 123 11 N no. A 123"19'\V

Sheet River 123'19W mi!e s 1 li Map a h - e h C 5 . 0 Features 123"20W 123'20'W 0 Geomorphic 123"21W 123"21W S6'N " 46 46"55"N 46"5n< Click here to return to map index 58'N 5rN 1sw · ,n 18W ' 123 11 no. J'1 A Sheet 123"19'W e l 123"t9W mi 1 Map - Model 0.5 123'2

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Geomorphic Features - Map Sheet no. 14

123•11w 123'16'W 123' 15W

Ch e h a l i

R iv e r

123'17'W 123' 16'W 123•1sw

N 0 0.5 1 mile A Click here to return to map index

Relative Elevation Model - Map Sheet no. 14

123•11w 123•1sw 123•1sw

46.SO'N

46*49'N

123' 17W 123' 16W 123' 15W

N 0 0.5 1 mile A Click here to return to map index

Geomorphic Features - Map Sheet no. 15

123"14W 123•13w 123•12w

46•50'N

46'49'N

lis C heha R i ve r

46°4 8'N

123' 14'W 123' 13W 123•12w

N 0 0.5 1 mile A Click here to return to map index

Relative Elevation Model - Map Sheet no. 15

123•14W 123' 13W 123•12w

123• 14w 123•13w 123• 12w

N 0 0.5 1 mile A Click here to return to map index

Geomorphic Features - Map Sheet no. 16

123"11W 123"10'W 123"9'W

46"50'N

46"49'N

River

C he ha 46"48'N lis

123"11'W 123' 10'W 123"9'W

N 0 0.5 1 mile A Click here to return to map index

Relative Elevation Model - Map Sheet no. 16

123• 11w 123•1ow 123•9w

46' 50'N

46' 49'N

46' 48'N

123' 11W 123' 10W 123' 9W

N 0 0.5 1 mile A Click here to return to map index

Geomorphic Features - Map Sheet no. 17

123' 8'W 123•7W 123' 6'W

46' 50'N

46•49'N

Chehalis

River 46• 48'N

123•sw 123' 7'W 123' 6'W

N 0 0.5 1 mile A Click here to return to map index

Relative Elevation Model - Map Sheet no. 17

123'8W 123' 7W 123' 6W

46•SO'N

46' 49'N

46' 48'N

123'8W 123' 7W 123' 6W

N 0 0.5 1 mile A Click here to return to map index

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Geomorphic Features - Map Sheet no. 24

r ve Ri

s l i h a Che

R iv er

N 0 0.5 1 mile A Click here to return to map index

Relative Elevation Model - Map Sheet no. 24

123•sw 123•7w 123.6W

46' 39'N

45•39•N

46'38'N

46' 38'N

46.37'N

46' 37'N

123' 8W 123' 7W 123' 6'W 123' 5W

N 0 0.5 1 mile A Click here to return to map index 23"TW 1 123"TW 25 N no. A 123'1!'W 123"8W Sheet e mil 1 Map

123"9W r

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123"9W i 0.5

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Geomorphic Features - Map Sheet no. 28

v i

alis eh h C

N 0 0.5 1 mile A Click here to return to map index

Relative Elevation Model - Map Sheet no. 28

123' 18'W 123' 17W 123' 16W

46' 38'N

46'37'N

46' 36'N

123' 18W 123' 17W 123' 16W 123' 1SW

N 0 0.5 1 mile A Click here to return to map index

Geomorphic Features - Map Sheet no. 29

123'18W 123' 17W 123'16W

46' 36N

46' 36'N

r ve Ri

46' 3S'N

46' 35'N s i l a h e h C

46' 34'N

123' 18W 123' 17W 123' 16W

N 0 0.5 1 mile A Click here to return to map index

Relative Elevation Model - Map Sheet no. 29

123•1aw 123' 17W 123' 16'W

46.36'N

46.35'N

45•34'N

123' 18W 123' 17W 123' 16W

N 0 0.5 1 mile A