Stabilizing Coastal Sand Dunes in the Pacific Northwesfgi
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S4Fík.^, United States Department of H Agriculture Stabilizing Coastal Sand Dunes Soil Conservation Service in the Pacific Northwesfgi V Agriculture (y Handbook 687 (/-' r r\> ' to CO o: . U3 33 CO ~J3 > fNi > ___ \<^^. 2r k 'JO o -< PRICE /V^ Cover: European beachgrass ¡s the dominant plant for stabilizing frontal dunes in the Pacific Northwest. Photo credits: All photographs were taken by Ron Nichols, pubfic affairs specialist (former photographer), Soil Conservation Service, ex- cept for the black and white historic photo- graphs. All programs and services of the U.S. Depart- ment OT Agriculture, Soil Conservation Ser- vice, are offered on a nondiscriminatory basis without regard to race, color, national origin, religion, sex, age, marital status, or handicap. August 1991 stabilizing Coastal Sand Dunes in the Pacific Northwest by Jack Carlson,' Frank Reckendorf,^ and Wilbur Ternyik' ' Plant materials specialist, Soil Conservation Service, West National Technical Center, Portland, Oregon. ^ Sedimentation geologist. Soil Conservation Service, West National Technical Center, Portland, Oregon. ^ Former plant materials technician. Soil Conservation Service, Plant Materials Nursery at Warrenton, Oregon; current nurseryman and private consultant. Wave Beachgrass Nursery, Florence, European beachgrass. Oregon. Contents Introduction 3 Marsh Habitats for Wet Interdune Areas 38 Extent and location of dunes 3 Description 38 Formation of dunes 5 Species and mixtures 38 The need for selective stabilization of dunes 8 Cover for Dredge Spoils 40 Planning a Dune Control Program 9 Approach 40 Land use 9 Species 40 Dune management areas 11 Mixtures 40 Site investigation 13 Maintenance 14 Case History: Warrenton Dune Control Project 41 Specifications 43 Sand-Stilling Dunegrasses for Initial Stabilization 15 Specifications for contracts 43 Species 15 Labor and equipment requirements 43 Unsuitable plants 18 Summary of recommended plant material 43 When to plant sand-stilling grasses 19 Planting stock 19 Literature Cited 48 Tools for planting 21 Methods of planting 21 Glossary 49 Fertilizing the plantings 22 Maintaining dunegrass stands 24 Appendixes 50 Establishing and maintaining a source of beachgrass 25 I Common and Scientific Plant Names Used in This Publication 50 II Beaches and Dunes Site Investigation Checklist 51 Permanent Cover 27 Species 27 List of Tables Native seed harvest 30 Table ^ Page Planting times and seed mixtures for grasses and legumes 30 1 Plants Not Recommended for Controlling Sand Seeding methods 32 Movement in Coastal Dune Areas 18 Fire control 32 2 Hill Spacing and Culms Per Acre for European Beachgrass 24 Woody plantings 33 3 Time Requirements or Work Rates for Three Types Planting methods 33 of Dune Stabilization Tasks 43 Maintenance 34 4 Basic Recommended Plant Material Chart for Dune Stabilization 44 Temporary Mechanical Aids 35 5 Transplants Needed with Varied Space Requirements 47 Landscape Plants for Stabilized Dunes 37 Ground covers 37 Medium shrubs 37 Trees 37 Introduction F Extent and Location of Dunes this publication draws upon the more than 50 years of infield dune The Pacific Northwest Coast is management experience of the U.S. defined as the area from Cape Department of Agriculture's Soil Mendocino, California, to the Strait Conservation Service (SCS). it re- of Juan de Fuca, Washington. This views fundamental dune-building area has a similar climate, vegeta- processes, describes how to plan a tion, soil, and geology, as well as dune-control program, and explains similar variation in wind and wave the mechanical aids, plants, and action. planting techniques for dune stabili- Many types of sand dunes and zation. sand spits, which make up 250,000 The recommendations in this acres of the Pacific Northwest coast, publication apply specifically to the provide exceptional recreational op- dune lands in the Pacific Northwest. portunities as well as rich habitat ar- Some of the plants, however, have eas for wildlife. Of the total dune been grown successfully as far north area, about 26,000 acres are dunes as Vancouver Island, Canada, and as with essentially no vegetation; and far south as Morrow Bay, California. of these, nearly 5,000 acres are "ac- (See appendix I for common and sci- tive" dunes that threaten competing entific plant names used in this pub- land uses. Active dunes, so called lication.) because they lack a stabilizing plant cover and are subject to extensive movement by wind action, advance onto forests, lakes, stream channels, roads, railroads, estuaries, and agri- cultural land. Every year several hundred acres of vegetated dune land are disturbed, mainly as a result of human activity, and become new active dunes. Landowners and community planners face the challenge of select- ing a dune stabilization plan that protects adjoining property and natural resources yet preserves suffi- cient open, active dune land for public recreation, aesthetics, and scientific purposes. To assist them. Typical dune development in early stages of natural revegetation. Residential and resort development are common on stabilized dunes, but vegetative cover must be maintained and managed to minimize sand deposition and damage to buildings. Building in beachgrass vegetation on or near foredunes is considerably more risky than further inland on much older stabilized dunes. Formation of Dunes break at an angle to the shoreline, from the northwest during the sum- Northwest coast. Their preliminary they generate a current that flows mer months. As a result, littoral drift results indicate longshore transport is changes direction from season to bounded by major headlands and is Coastal dune formation is deter- parallel to the shoreline (Komer season. highly correlated to the prevailing mined by four factors: wind action, 1976). This current, together with Recent work (Chesser and wave approach angle. They also wave action, vegetation, and source the waves, produces a transport of sand along the beach known as lit- Peterson 1987) based on physi- concluded that episodic events may of sand. The two immediate sources ographic and minéralogie analysis overshadow seasonal cycles of of dune sand particles are the ero- toral drift (Komer 1979). Winds and indicates that there are at least 1 7 transport. sion of coastal formations exposed to associated waves arrive from the major littoral cells along the Pacific wave attack, and sediment load from southwest during winter months and rivers. Ocean currents move sand from eroding headlands, and from the mouths of rivers, to where there are indentations in the coastline. As sand is deposited on beaches, it is exposed at low tide, dries quickly, is caught by the wind, and is carried inland. Along the Pacific coast there is almost always a moderate wind. At times the wind approaches hurri- cane force. High-velocity winds move enormous amounts of sand in- land. After a winter storm, rivers and streams carry a heavy load of sedi- -^ ments from the upper watershed. This sand is combined with that de- rived from storm waves attacking sea '^' . cliffs, dunes, and spits. These storms >/./*? provide a seasonal near-shore sand supply, whereas lower-energy waves and currents, which occur more on a continual basis, transport the near- shore sand to beaches and tidal in- lets (Peterson et al., 1982). Waves reaching the coast gener- ate longshore currents in the near- shore area that are important in the movement of sand along the beach and in beach erosion. When waves Dunes form and reform naturally or from human activities. Concentrated wind channels frequently create blowouts, or areas where wind removes existing vegetation. The three largest littoral cells are wind and trap the sand. Thus, in- associated with the three largest riv- stead of a hummocky landscape or a ers—the Columbia, the Umpqua, series of transverse and oblique and the Eel (Chesser and Peterson ridges of barren sand, a grassy 1987). Therefore, it is no surprise foredune develops parallel to the that some of the largest dune areas coastline (Cooper 1958). The great- occur in areas near these major riv- est amount of sand movement along ers. Jetty construction on the Pacific the North Pacific coast takes place Northwest coast also has a major ef- during the high-velocity winter wind fect on littoral sand drift and accu- storms. At this time sand engulfs the mulation. Sand accumulates on both foredune vegetation. During the the north and south sides of jetties spring and summer, however, veg- from the seasonally reversing waves. etation grows up through the sand Embankments, formerly at the mouth and forms a lush growth. This is cov- of rivers, are filled with sand. This ered again the next winter, and a sand accumulation can be quite fast, continuous sand ridge, built layer by such as behind the south jetty of the layer, extending without interrup- Columbia River. Between 1885 and tion, and parallel to the coastline, re- the 1930's, a prograding beach de- sults. The lands lying to the leeward veloped in this area, resulting in of the foredune are protected from 3,000 acres of open, active sand the scouring action of the sand-laden dunes. wind and a dense sod or forest cover Vegetation is a major factor af- eventually develops. fecting dune formation. Along a bar- If sand is deposited more rapidly ren shore, dunes are oriented than it is blown inland, the beach transversely or obliquely to the line will build oceanward. The veg- wind, depending on the existing etation will advance to a new storm wind regime. Prior to 1900,