Chess chile be Caast, Eng: Ch CETA 82-3 Shore Erosion Control with Salt Marsh Vegetation by Paul L. Knutson and Margaret R. Inskeep COASTAL ENGINEERING TECHNICAL AID NO: 82-3 FEBRUARY 1982 Veg, Fae ax8 Mening oo Approved for public release; distribution unlimited. U.S. ARMY, CORPS OF ENGINEERS COASTAL ENGINEERING RESEARCH CENTER Kingman Building Fort Belvoir, Va. 22060 republication of any of this material Army Coastal Reprint or shall give appropriate credit to the U.S. Engineering Research Center. Limited free distribution within the United States of single copies of this publication has been made by Additional copies are available from: this Center. Nattonal Technical Information Service Operations Divitston ATTN: 0285 Port Royal Road 22161 Springfteld, Virginia The findings in this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents. NM TT i ty UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGE (When Data Entered) READ INSTRUCTIONS REPORT DOCUMENTATION PAGE 1. REPORT NUMBER 2. GOVT ACCESSION NO.| 3. RECIPIENT'S CATALOG NUMBER CETA 82-3 TITLE (and Subtitle) 5. TYPE OF REPORT & PERIOD COVERED Coastal Engineering SHORE EROSION CONTROL WITH SALT MARSH Technical Aid AUTHOR(s) 8. CONTRACT OR GRANT NUMBER(s) Paul L. Knutson Margaret R. Inskeep PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT, PROJECT, TASK AREA & WORK UNIT NUMBERS Department of the Army Coastal Engineering Research Center (CERRE-CE) Kingman Building, Fort Belvoir, Virginia 22060 631530 . CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATE Department of the Army February 1982 Coastal Engineering Research Center 13. NUMBER OF PAGES Kingman Building, Fort Belvoir, Virginia 22060 24 14. MONITORING AGENCY NAME & ADDRESS(if different from Controlling Office) 15. SECURITY CLASS. (of thie report) UNCLASSIFIED Sa. DECL ASSIFICATION/ DOWNGRADING SCHEDULE 16. DISTRIBUTION STATEMENT (of thie Report) Approved for public release, distribution unlimited. DISTRIBUTION STATEMENT (of the abstract entered in Block 20, if different from Report) 18. SUPPLEMENTARY NOTES KEY WORDS (Continue on reverse side if necessary and identify by block number) Erosion control Salt marsh vegetation Planting guidelines Shoreline stabilization. ABSTRACT (Continue on reverse side if necessary and identify by block number) Salt marsh plants are effective in stabilizing eroding shorelines in many sheltered coastal areas. Exceptional results have been achieved in a variety of intertidal environments at a fraction of the cost required for comparable structural protection. Techniques are available for the efficient propagation of several marsh plants for use in shore stabilization. This report provides a method for determining site suitability, establishes guidelines for planting marshes to control erosion, and compares the costs of vegetation to structural methods of erosion control. FORM DD . jan 73a 1473 = EDITION OF 1 NOV 6515S OBSOLETE UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGE (When Data Entered) ‘decile apeamitige INT eMS ae VRE: Oise: at ee La OTR { : a dairy apis ui 5 Css: 4 Ou 1 mee Om SY) ae Sk et = re § rr a ns ace fects dct) as ahhh DrpFprving oI Ria nee ij ‘ , sae UE epshiin ye eceen or nsicolh anh a SLamsglbleh AGM ve wll: Wty een ar P f; : Aa ancl Nati gem Pg Se eatihe 4 ‘ j i TORS hee oe Maia Hitec bl tars Ns — try ohne me Leder eal ages 4 { =t t ' in gy ne a ml gee ag cmmmigmes: me. Bo DWasg: Py ages LIF ee BA LeU) as hl ae ceri 1) aE Rey Bri 4 } f é TAry vena 4 aa AS i RELATE A athe Lie vec a) ‘es 9 sm Nea Aa te barra gre belo nee ha nimi la te wo hace dalle a sch aly wa iw tery Styeae ee ot RT ee 4%) L PREFACE This report provides criteria for planting salt marsh vegetation to control erosion. It is intended to update information presented in "Planting Guidelines for Marsh Development and Bank Stabilization,” CETA /7/7-3 (Knutson, 1977) and “Wetland Habitat Development with Dredged Material: Engineering and Plant Propagation,” TR DS-/8-16 (U.S. Army Engineer Waterways Experiment Station, 1978). The work was carried out under the coastal ecology research program of the U.S. Army Coastal Engineering Research Center (CERC). The report was prepared by Paul L. Knutson and Margaret R. Inskeep, Coastal Ecology Branch, under the general supervision of E.J. Pullen, Chief, Coastal Ecology Branch, Research Division. Illustrations were prepared by L. Martin. Comments on this publication are invited. Approved for publication in accordance with Public Law 166, 79th Congress, approved 31 July 1945, as supplemented by Public Law 172, 88th Congress, approved 7 November 1963. TED E. BISHOP Colonel, Corps of Engineers Commander and Director CONTENTS Page GORMRSTON AYNCHORS > WoSc CUSINOMNSE AKO) IMIG CSIL)ocooccacccoc00G00000 5) I JENA LOWDOKG LON Kis SOOO OO ODIO OOOO OOO OOD UO OOOO SOOO OOUGUSOOOUOGOSUOO 000 7 IL BACKGROUND crevevercvcieleverote leenevelehetelcvlelotetciolercioncretereloncteneneiclercvenccckorersioncteleleiotenenseneinan 7 SDE TE RMEN TENG SSiehhe S UMsRAB Mee Yecreveyeielekelohellelelelicl olelel sie) clielelelorekeloheolelelolehehelekekererene 7 Noi elanigullineyeriaves MEI) WIGNER 96 CG OCOD DOO O OOD D ODD OUD O0000O00000000000 7 Zo Other Environment allaba CteorSteloieieieleler el slalererelereleiel eleisloielel oiol el eielelerercron ners lO) IV PLANTING GUIDELINES <<. 42/0 sistsin «tis ciatove olererels ers) ste-niciele Siete cintels ee CRORE REO I. 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Pilanting Specifications, for Prineipall Specilesieje.\clslelerercieteleloloneetetenmnles BY Other Useful SX KISS OOOO OOOO UCD DUOMO OO COOOOO UCDO OOOO 000000000 16 V EHRGTISTTEZANTO MO Nictovenotiohelietelrelicveuelevobeloteleere)cliel cickerelcrolekchel eneiieiolioleleleneicveteloveletenoonenenenenete 19 VI MUAUIUN UE NIAIN GEistanenenotetoieterolieteneiel ovetellereilelevetercloloverencicieveleletchercloleieiebelctencrcheretonenorenenenenene 20 VIL COSTS herctrerokevotonclcterciciichotolercteyel ciel crcval ciiciclickelovelchelchelielevolheneneieheleheleletansuciereiehenciobenenenonenene 20 \WALICIL EXAMPLE EROBIGEMCrcnctelorehelstioneielcleneielerensiel cleheleroletelerenelieleleloicnerehereielereieleroneltclonenetenenele Dik LITERATURE GISTED eievotercievolicliclevevelolcicveterelelctelcleleieroielecclenelicielelsronctolenclerorerolchelencnenetene 24 FIGURES 1 Oldest recorded salt marsh plantingecceecccecccecsccrcescccsevscccevece 8 2 Vegetative stabilization site evaluation forme .cecccccsccccceccccccce 9 3) SMoOoO EN Condens Boles qcoccd0000D0DDD00DDODDDODRDDOODDDRDDDODOOOCN00000.— LIL 4 Hand planting by workers from North Carolina State at Raleigh......-.. 12 5 Machine planting by workers from North Carolina State at Raleigh....-..- 12 ) SieKoKelN CopealtacAISIGo GoG0DOO ODOC OO ODD DOU DD DDD0DDDDDNDDDDOOODDDOOOOOOCO0000. IA 7 Pacific COTAUZLASSe cocccevccccvcveveccceccccccveceseceseccesececesccece 115) Shame BeGkw@55oc00n0d00 OUD DU OO DODO OKO ODDDDOODDDODDDDOODODDODUDOOO0D000.. IY 9 Tufted HALLZLASSececevevcececeveccceveccscecscveseseereceseceseeeseses 18 10 Cost comparison of various shore stabilization methods...eeccccceeveee 21 CONVERSION FACTORS, U.S.- CUSTOMARY TO METRIC (SIL) UNITS OF MEASUREMENT U.S. customary units of measurement used in this report can be converted to metric (SI) units as follows: Multiply by To obtain TnehoS a Ga 25.4 millimeters 2254 centimeters square inches 62452 Square centimeters cubic inches 16.39 cubic centimeters feet 30.48 centimeters 0.3048 meters square feet 0.0929 square meters cubic feet 0.0283 cubic meters yards 0.9144 meters Square yards 0.836 square meters cubic yards 0.7646 cubic meters miles 1.6093 kilometers Square miles 259.0 hectares knots 1.852 kilometers per hour acres 0.4047 hectares foot-pounds 1.3558 newton meters MLL ERS Lo ONGY sz 1073 kilograms per square centimeter ounces 28.35 grams pounds 453.6 grams 0.4536 kilograms ton, long 1.0160 metric tons ton, short 0.9072 metric tons degrees (angle) 0.01745 radians Fahrenheit degrees 5/9 Celsius degrees or Kelvins! lT> obtain Celsius (C) temperature readings from Fahrenheit (F) readings, use formula: C = (5/9) (F -32). To obtain Kelvin (K) readings, use formula: K = (5/9) (F -32) + 273.15. HAMA T BAR Qf hasyarios age 1a) Geers Lib Pos 4 By WoW, =} ; na ee ay batt ani co a ; se rei , ‘ bey her “poche: : apa). a Wi ay.” frie She haobase . ti ty Ww ala) he bay . Rae. hed Hh eee Lia mii ( i mi [Siw » « ’ 5 lah an) Wiss” ae taxivab. thik wo ie situa: ax idle Pree = Saga omenair ram cin mre one Lagrtbsed ¢ Sy Stare oh det oars ‘dt Tod ° 330 orks ba y ee 3 er eer ee eee CL eEVE te Chem A) COVS) mad, aaah ins Lane ts RW eR eR a4 + mid Wilkie ac wv, Wins Ooeng rhe i oe SHORE EROSION CONTROL WITH SALT MARSH VEGETATION by Paul L. Knutson and Margaret R. Inskeep I. INTRODUCTION Erosion in salt and brackish water areas of the contiguous United States can be controlled either structurally or with recently developed nonstructural techniques using native marsh plants. Vegetation, where feasible, is usually more cost-effective than structures built to control erosion. This report provides a method for determining site suitability, establishes guidelines for planting marshes to control erosion, and compares the costs of vegetation to structural methods. II. BACKGROUND Coastal marshes are herbaceous plant communities along shorelines periodically flooded by salt or brackish water. Vulnerability to wave attack during early stages of establishment prevents the natural invasion of marshes along many shorelines. Even mature natural marshes may suffer permanent damage from severe storms. A common form of damage is the formation of a scarp or bank on the seaward edge of the marsh. Once a scarp is formed it becomes a focal point of continued erosion. Both natural and planted marshes (Fig. 1) function in three ways to reduce shore erosion: (1) wave attenuation, (2) sediment capture, and (3) sediment stabilization. Both wave attenuation and sediment capture are directly related to stem density and marsh width (landward to seaward) (Dean, 1978). Stem density is dependent on many variables, including (1) species, (2) geographical area, (3) elevational zone within the marsh, (4) season, (5) Maturity of the marsh, and (6) wave climate. Marsh width is influenced by shore slope and tidal range. During the winter when the aerial stems provide only limited resistance to wave energy, the sediment stabilizing function of the plant roots becomes critical. Root mass may increase the shear strength Of Soils) bya factor lof Zeon 3 (Gray, 19/4). Planted marshes can often succeed on shorelines where natural processes have failed to provide plant cover. These marshes, like natural marshes proceed through a cycle which includes a period of establishment, a period of stability, and a period of erosion, where wave-induced erosion is a factor (Knutson, et al., 1981). The functional life of planted marshes will be shorter in areas where waves are more sSeveree III. DETERMINING SITE SUITABILITY 1. Evaluating Wave Climate. ae Indicators of Wave Severity. In brackish and salt water tidal areas, wave climate severity has a major influence on marsh establishment. Three shoreline characteristics--fetch, shore configuration, and sediment grain size--are useful indicators of wave climate severity and planting success (Knutson, et al., 1981). Fetch, the distance the wind blows over water to generate waves, is inversely related to successful erosion control. Shore Figure 1. Oldest recorded salt marsh planting (planted in 1928), Cherry Stone Inlet, Virginia. configuration, the shape of the shoreline, is a subjective measure of the shoreline's vulnerability to wave attack. For example, a cove is relatively sheltered while a headland is vulnerable to wave attack from many directions. The gratin size of beach sands is also related to wave energy. Fine-grained sands frequently indicate low energy beaches while coarser materials indicate higher energy beaches. Two additional factors should be considered when evaluating wave climate--boat traffic and offshore depth. Shore areas in close proximity to boat traffic will be subject to ship-generated waves. Shallow offshore depths impede the development and growth of larger waves. However, no method is available for numerically evaluating boat traffic and offshore depth. be Method for Evaluating Wave Climate. Knutson, et al. (1981) developed a method for evaluating wave climate based on observed relationships between fetch, shore configuration, grain size, and success in controlling erosion in 86 salt marsh plantings in 12 coastal states. The method evaluates planting potential on a case-by-case basis, using a vegetative stabilization site evaluation form (Fig. 2). Each of the four Shore Charactertstics on the form is measured for the area in question, the Descriptive Categories best describing the area are identified, and the Weighted Score associated with each descriptive category is notede A Cumulative Score is calculated, and the success rate associated with the appropriate range of cumulative scores is noted under Score Interpretation. Sites with a cumulative score of 300 or greater (observed success rate of 80 to 100 percent) are very promising planting environments. However, even sites with a cumulative score of 201 to 300 (observed success rate of 30 to 80 percent) will often constitute an acceptable risk considering the higher costs associated with structural shore protection alternatives (see Sec. VIL). be SlOle CHARACTERISTICS a. FETCH-AVERAGE AVERAGE DISTANCE IN KILOMETERS (MILES) OF OPEN WATER MEASURED PERPENDICULAR TO THE SHORE AND 45° EITHER SIDE OF PERPENDICULAR 2. DESCRIPTIVE CATEGORIES | 3 (SCORE WEIGHTED BY PERCENT SUCCESSFUL) WEIGHTED SCORE GREATER THAN 9.0 b. FETCH-LONGEST LONGEST DISTANCE IN KILOMETERS (MILES) OF OPEN WATER MEASURED PERPENDICULAR TO THE SHORE OR 45° EITHER SIDE OF PERPENDICULAR i (5.6) i ce 2. 6.1 | GREATER | - THAN Bo c. SHORELINE GEOMETRY GENERAL SHAPE OF THE SHORELINE AT THE POINT OF INTEREST PLUS 200 METERS (660 FT) ON EITHER SIDE | d. SEDIMENT GRAIN SIZE OF SEDIMENTS IN SWASH ZONE (mm) MEANDER OR => STRAIGHT ~ less than 0.4 04-08 4 CUMULATIVE SCORE 9. SCORE INTERPRETATION a. CUMULATIVE SCORE b. POTENTIAL 9 SUCCESS RATE Figure 2. 122 = 200) ZOl = 300) 300 — 345 30 to 80% 80 to 100% Vegetative stabilization site evaluation form. 2. Other Environmental Factors. Salinity is a major stress on all plants growing within the intertidal ZONE€e However, the species specified for use in this report are all salt tolerant. The salinity tolerance range for each species is presented in the following section on planting guidelines. Soil type will mainly affect the planting technique and need for ferti- lizer since most salt marsh plants tolerate a wide range of substrates. The actual planting will be easier in loose sandy soils than in heavy plastic or very compact soils. Strong tidal action can undermine plantings; therefore, location and migration of tidal channels in the vicinity of prospective plantings should be considered. The presence of healthy marsh patches on or near the site is an excellent indicator that there are no environmental factors which are likely to limit plant establishment at the site. IV. PLANTING GUIDELINES 1. Selecting Plant Species. For erosion control projects, the intertidal zone is the most critical area to be planted and stabilized. If a healthy band of intertidal marsh can be established along a shore, revegetation of the slope behind it will occur through natural processese Four species of pioneer plants have demonstrated potential in stabilizing the part of the intertidal zone which is in direct contact with waves: smooth cordgrass (Spartina alternitflora) along the gulf and Atlantic coasts, Pacific cordgrass (Spartina foltosa) on the Pacific coast from Humboldt Bay south to Mexico, and Lyngbye's sedge (Carex Lyngbyet) and tufted hairgrass (Deschampsta caespitosa) in the Pacific Northwest. oe Srl Preparation. The width of the substrate at an elevation suitable for plant establish- ment will determine in part the relative effectiveness of the erosion control planting. A practical minimum planting width for successful erosion control is 20 feet (6.0 meters) (Knutson, et al., 1981). On the Atlantic and gulf coasts, marsh plants will typically grow in the entire intertidal zone. Marsh plants seldom extend below the elevation of mean tide on the southern Pacific coast or below lower high water in the Pacific Northwest. Because of these elevational constraints, the more gradual the shore slope, the broader the potential planting width. On steeply sloping shores, there may be little area suitable for planting. If the potential planting area is not 20 feet in width, the shore must be sloped or backfilled to extend ite Backfilling must be done enough in advance of planting to allow for settling and firming. Salt marsh plants rely heavily on exposure to direct sunlight and will not grow in shaded areas. Therefore, any overstory of woody vegetation present at a site should be cleared above the planting area and landward to a distance of 10 to 15 feet (3 to 5 meters). 10 3. Planting. Vegetative transplants are used for erosion control plantings as direct seeding is very unlikely to be effective on sites subject to erosion. Vegetative transplant types include (a) sprigs, stems with attached root material (Fig. 3); (b) pot-grown seedlings; or (c) plugs, root-soil masses containing several intact plants dug from the wild. Sprigs are the least expensive to obtain and easiest to handle, transport, and plant. They may be obtained from field nurseries, planted at least a year in advance, or col- lected from young marshes or the edges of expanding established marshes. Pot- grown seedlings are more expensive to grow and plant, more awkward to handle and transport, but relatively easy to produce and are superior to sprigs for late season plantings. Plugs are the most expensive to obtain, difficult to transport, and should probably be used only when no other sources are avail- able. Plugs are usually necessary only when a dense root mat or cohesive sediments in the harvest area complicate the separation of plants into sprigs. The Soil Conservation Service may be helpful in locating and obtaining plant materials. A Soil Conservation Service State conservationist is located in all the State capitals. Figure 3. Smooth cordgrass sprig. Requirements for the successful transplanting of salt marsh plants include (a) opening a hole or burrow deep enough to accommodate the plant, (b) keeping the hole open until the plant can be properly inserted, (c) inserting the plant to the full depth, (d) closing the opening, and (e) firming the soil around the plant. Three to five sprigs are inserted in each planting hole. Plugs and pots are planted individually. Planting must be done during low water when the site is exposed. Hand planting (Fig. 4), using dibbles, spades, and shovels, is the most practical method for small-scale plantings (less than 1 acre). ila Figure 4. Hand planting by workers from North Carolina State at Raleigh (photo courtesy of W.eW. Woodhouse, Jr., ED. Seneca, and S.We Broome, North Carolina State at Raleigh). Normally, planting crews work in pairs with one worker opening holes and the other inserting the plant and closing the hole. The fertilizing may be done by a third worker during planting or may be handled as a separate opera- tion. Machine planting (Fig. 5) of sprigs, where the terrain allows, can do a Figure 5. Machine planting by workers from North Carolina State at Raleigh (photo courtesy of W.-W. Woodhouse, Jr., E.D. Seneca, and S.We Broome, North Carolina State at Raleigh). 12 more uniform job and is far more economical than hand planting in large-scale plantings. The tractor-drawn planters used for planting cabbage, tomatoes, tobacco, etc., require either no alteration or a simple adjustment of the row opener for certain soils. Barriers to machine planting are inadequate traction on compact substrates, insufficient flotation on soft sites, or the presence of tree roots or stones (Woodhouse, 1979). Planting depth is basically independent of the method or material used. Most species do best when planted 1 or 2 inches (3 or 5 centimeters) deeper than they were growing. Where erosion is expected, deeper planting is recom- mended. If, on the other hand, deposition is likely, plants should be set very close to the depth they were growing when dug or when removed from pots (Woodhouse, 1979). 4. Planting Specifications for Principal Species. ae Smooth Cordgrass (Fig.6). (1) Planting techniques--sprigs, pot-grown seedlings or plugs. (2) Plant spacing--3 feet (1 meter) on sheltered sites (4,000 transplants per acre), 1.5 feet (0.5 meter) on exposed sites (16,000 propagules per acre). (3) Planting zone--mean low water to mean high water where the tidal range is less than 6 feet (2 meters); mean tide to mean high water where tidal range is greater than 6 feet. (4) Planting width--the entire planting zone should be planted when practicable. However, there is typically no advantage in planting to a width of more than 60 feet (20 meters). A practical minimum width is 20 feet or 60 percent of the intertidal zone, whichever is larger. When only a part of the planting zone is to be planted, the planting should be from mean high water seaward. (5) Salinity range--5 to 35 parts per thousand. (6) Optimal planting dates--northern range, April and May; Mid- Atlantic, March, April, and May; southern range, February, March, April, and May. b. Pacific Cordgrass (Fig. 7): (1) Planting techniques--sprigs, pot-grown seedlings or plugs. Since the natural spread of Pacific cordgrass is relatively slow, no more than 10 percent of harvest area should be disturbed when col- lected in the wild. (2) Plant spacing--1.5 feet (16,000 propagules per acre). (3) Planting zone--mean tide to mean low high water. (4) Planting width--the entire planting zone should be planted when practicable. However, there is usually no advantage in planting to a width of more than 60 feet. A practical minimum width is 20 feet or 60 percent of the upper one-half of the intertidal zone, whichever is larger. When only part of the planting zone is to be planted, the planting should be from mean low high water seaward. Ls ae Seed head (inflorescence) b. Distribution (shaded area) Figure 6. Smooth cordgrass. 14 ae Seed head (inflorescence) be Distribution (shaded area) Figure 7. Pacific cordgrass. 15 (5) Salinity range--less than 35 parts per thousand. (6) Optimal planting date--March and April. ce lLyngbye's Sedge (Fig. 8): (1) Planting technique---sprigs. Plants can be readily moved from high to low salinity sites but not the reverse. (2) Plant spacing--1.5-foot centers or about 16,000 plants per acre. (3) Planting zone--mean lower high water to mean higher high watere (4) Planting width--the entire planting zone should be planted when practicable; however, there is typically no advantage in plant- ing to a width of more than 60 feet. A practical minimum width is 20 feet or 60 percent of the planting zone, whichever is greater. When only part of the planting zone is to be planted, the planting should be from mean higher high water seaward. (5) Salinity range--O to 20 parts per thousand. (6) Optimal planting period--April, May, and June. de Tufted Hairgrass (Fig. 9): (1) Planting technique--sprigs. (2) Plant spacing--3 feet or about 4,000 transplants per acre. (3) Planting zone--mean higher high water and above. (4) Minimum planting width--none. (5) Salinity range--fresh and brackish. (6) Optimal planting period--April, May, and June. 5. Other Useful Species. The above four species, generally the effective pioneers in the intertidal zone, provide an environment into which other species may invade. In some cases, however, planting of the entire slope is advisable to control erosion caused by storm tides, surface runoff, or wind. The species potentially useful in such cases are as follows: (a) Black needle rush (Juncus roemerianus) (b) Common reed (Phragmites australis) (c) Cordgrasses: (1) Big cordgrass (Spartina cynosuroides) (2) Gulf cordgrass (Spartina spartinae) (3) Saltmeadow cordgrass (Spartina patens) 16 ae Seed head (inflorescence) be Distribution (shaded area) Figure 8. Lyngbye's sedge. 17 ae Seed head (inflorescence) b. Distribution (shaded area) Figure 9. Tufted hairgrass. 18 (d) Mangroves: (1) Red (Rhizophora mangle) (2) Black (Avtecennia germinans) (3) White (Laguneularia racemosa) (e) Saltgrass (Distichlis sptcata) (f) Seaside arrowgrass (Triglochin maritima) (g) Siltgrass (Paspalum vagtnatum) V. FERTILIZATION Fertilization is recommended for all plantings subject to wave stress except where previous experience has indicated it is not needed. Two general types of fertilizer can be used--soluble or slow release. Soluble materials should be broadcast and disked in before planting, spread in the planting furrow, placed in a second hole beside the planting hole, or placed in the bottom of the planting hole and covered with soil before the plant is inserted. Slow-release materials, such as Osmocote or Mag Amp, should be effective when applied in the planting hole or furrow. If soluble materials are used, they should be applied at a rate of 100 pounds per acre (1 kilonewton per hectare) of nitrogen (N) and 100 pounds per acre of phosphate (Po 0g ) at time of planting. In conventional mixed ferti- lizers, the number designations such as 10-10-10 represent the percentages (by weight) of nitrogen (N), phosphate (P)0,), and potash (K20), respectively, in the mixture. Therefore, the amount of 10-10-10 fertilizer per acre needed to provide 100 pounds of nitrogen and 100 pounds of phosphate would be 1,000 pounds. A topdressing of an additional 100 pounds per acre of soluble nitro- gen (N), 6 to 8 weeks after planting, will be helpful on deficient sites and a third 100-pound application 6 weeks later will be advisable on acutely defi- cient sites. Slow-release materials, if used in lieu of soluble fertilizer, should be applied at a rate of 100 pounds per acre of nitrogen at time of planting. Slow-release materials should always be placed in the planting hole or furrowe For conventional slow-release mixtures (14-14-14 or 16-8-12), about 0.5 ounce (15 grams) of fertilizer should be placed in each hole.- When slow- release materials are used, no additional applications are necessary during the first growing season. If plant cover and development are not adequate by the second growing season, fertilize again with 100 pounds of nitrogen using a soluble source broadcast at low tide in early spring. After establishment, the color of the grass itself can be used as a general indicator of available nitrogen. Dark green leaves indicate an adequate supply while lighter shades of green and yellowing lower leaves during active growth result from too little nitrogen. Wg) VI. MAINTENANCE Once a site is planted, it will be necessary to keep it free from debris that might smother the plants, especially during the first two growing seasonSe Litter such as wood, styrofoam, algae, and dislodged submerged plants forming a strandline should be removed in both the fall and the spring. Another source of possible plant damage in some regions is predation from Canada and snow geese which are fond of the roots and rhizomes of marsh plants. Rope fences on the seaward edge of the marsh will exclude waterfowl during the first few growing seasons. Fences should consist of wood, metal, or plastic pickets strung with nylon rope spaced at 6-inch (15 centimeter) intervals from the sediment surface to mean high water (E.W. Garbisch, Environmental Concern, Ince, personal communication, 1977). VII. COSTS The principal cost of a project (unless site preparation or temporary protection is required) is the labor required to obtain or produce propagules and plant theme Harvesting and planting must usually be confined to about a 5-hour period per tide which substantially affects the cost of labor. Smooth cordgrass, Pacific cordgrass, Lyngbye's sedge, and tufted hair grass sprigs can be harvested, processed, and planted by hand at a rate of about 10 man- hours per 1,000 sprigs. Using plugs of any species is at least three times more time-consuming than using sprigs (30 man-hours per 1,000 plugs). Pre- paring and planting nursery seedlings of any species takes about 23 man-hours per 1,000 seedlings. To estimate labor requirements for a particular project, first determine the number of planting units required as follows: 1 No. of planting units = area of planting x (plant spacing)? (Plant spacing for erosion control projects is typically 1.5 feet.) Second, determine the labor required to prepare and plant these units as follows: ired = i Sean hours aaa Labor required = Noe of planting units x 1,000 planzina omitc (As noted above, sprigs require about 10 man-hours per 1,000 planting units, plugs about 30 man-hours per 1,000 planting units, and nursery seedlings about 23 man-hours per 1,000 planting units.) The cost of fertilizer varies but will probably cost no more than $50 to $100 per acre (1980) including labor or about 5 to 10 cents per linear foot for a 30-foot-wide (10 meter) planting. Slow-release fertilizer is more expensive, about $500 to $1,000 per acre or $0.50 to $1.00 per linear foot for a 30-foot-wide planting. However, the use of slow-release materials will eliminate the need for postplanting fertilizer applications. Figure 10 compares planting costs per foot with the costs per foot of several alternative structural devices. (Labor costs assumed to be $15 per hour plus 100 percent overhead.) Vegetative stabilization is lower in cost than any structural erosion control measure. 20 300 50 40 & = 28 - ao ° (=) 20 15 9 4 Wood Sheeting Gabions Rock Sandbag Marsh Marsh Bulkhead 3 Feet High Revetment Revetment 30 Feet Wide 30 Feet Wide 3 Feet High 3 Feet High 3 Feet High Plonted with Planted with Nursery Sprigs Seedlings Figure 10. Cost comparison (dollars per linear foot) of various shore stabilization methods (structural costs after Eckert, Giles, and Smith, 1978). Design life of vegetative stabilization projects is about 5 to 10 years (Knutson, et ale, 1981), which is comparable to other low-cost shore protec— tion measures. EXAMPLE PROBLEM The following examples demonstrate the use of guidelines for a property owner who wishes to stabilize 300 feet (90 meters) of shoreline: 1. Determining site suitability: GIVEN: The shoreline is located along a tidal river. The distance across the river (fetch perpendicular to shore) is about 0.6 mile (1 kilometer). The distance across the river 45° to either side of perpendicular is about 0.9 mile (1.5 kilometers). The shoreline is relatively straight and the sand on the eroding beach is fine (0.25 millimeter). Dal FIND: Determine the likelihood of successful stabilization with salt marsh vegetation at this site using the vegetative stabilization site evaluation form (Fig. 2). SOLUTION: The cumulative score for this site is 87 + 89 + 62 + 84 = 322, which indicates that successful stabilization at this site is nearly certain. 2. Selecting plant species: GIVEN: Property is on the Atlantic coast. FIND: Determine the appropriate species to plant in this region. SOLUTION: Smooth cordgrass would be the proper plant to use in this area (see Saxe5 IV 5c 3. Preparing the site: GIVEN: The property owner estimates that the wetted part of the intertidal zone (mean high water to mean low water) is about 30 feet (9 meters) wide. Tidal range on the river is about 1.5 feet. About one-half of the shoreline is shaded by trees. FIND: What site preparation is needed at this site? SOLUTION: Smooth cordgrass grows throughout the intertidal zone in areas where tidal range is less than 6 feet (Sec. IV,2). Therefore, the entire wetted part of the intertidal zone (30 feet) can be planted. Because this exceeds the minimum width for erosion control plantings (20 feet), no shoreline sloping or backfilling will be necessary. However, the trees shading the shoreline will have to be cleared for a distance of 10 to 15 feet landward of mean high water (Sec. IV,2). 4. Planting specifications: GIVEN: There are several natural stands of cordgrass near the site, and there is a 30-foot-wide shoreline available for planting. FIND: Determine the width and overall area of the planting, the type of transplant that will be used, plant spacing, and the method of planting. SOLUTION: It is recommended for smooth cordgrass (Sec. IV,4) that the entire available planting zone be planted when practicable. Therefore, the planting width should be 30 feet, and the area of the planting is 30 feet by 300 feet or 9,000 square feet. Sprigs are the lowest cost type of transplant and are available from natural stands near the site. Hand planting would be favored on this site because the area of the site is less than 1 acre (43,560 square feet) and there is a possibility of encountering tree roots during planting. 22 5. Fertilization: GIVEN: The property owner has elected to use a soluble fertilizer which has a composition of 10-10-10 because of its lower cost. FIND: Determine the amount of fertilizer that will be required for the initial application. SOLUTION: Initial fertilization with soluble fertilizer is 100 pounds of nitrogen (N) and 100 pounds of phosphate per acre (43,560 square feet). This planting is 9,000 square feet or 0.2 acre (0-1 hectare) and will require 20 pounds of nitrogen--20 pounds of phosphate. 10-10-10 fertilizer is 10 percent nitrogen and 10 percent phosphate by weight. Therefore, 200 pounds of fertilizer will be needed to provide the 20 pounds of nitrogen and 20 pounds of phosphate needed for this planting (see Sec. V). 6. Estimating planting costs: GIVEN: The planting is 9,000 square feet in size, and sprigs will be used at a spacing of 1.5 feet. FIND: Determine the number of planting units and man-hours required to plant this project. SOLUTION (see Sec. VII): (1) No. of planting units = area of planting x A (plant spacing)? or 4,000 planting units = 9,000 square feet x aaa’ feet G5) 3 te: é P man-hours (2) Man-hours required = No. of planting units x 1,000 planets wmtes or 10 man-hours 40 man-hours = 4,000 planting units x 1,000 planting units 23 LITERATURE CITED DEAN, R.G., “Effects of Vegetation on Shoreline Erosional Processes,” Reprint, Wetland Functions and Values: The State of Our Understanding, American Water Resources Association, Minneapolis, Minn., Nov. 1978. ECKERT, J.W., GILES, MeLe, and SMITH, G.M., “Design Concepts for In-Water Containment Structures for Marsh Habitat Development,” TR D-/8-31, Dredged Material Research Program, U.S. Army Engineer Waterways Experiment Station, Vicksburg, Miss., July 1978. GRAY, D.M., “Reinforcement and Stabilization of Soil by Vegetation," Journal of Geotechnical Engineering Dtvtston, Vol. 100, Noe GT6, June 1974, pp. 696- 699. KNUTSON, P.L., “Planting Guidelines for Marsh Development and Bank Stabiliza- tion,” CETA 77-3, U.S. Army, Corps of Engineers, Coastal Engineering Research Center, Fort Belvoir, Va, Aug. 19/77. KNUTSON, P.Le, et ale, “National Survey of Planted Salt Marshes, Vegetative Stabilization and Wave Stress,” Wetlands, Journal of the Soctety of Wetland Setenttsts, Sept. 1981. U.S. ARMY ENGINEER WATERWAYS EXPERIMENT STATION, “Wetland Habitat with Dredged Material: Engineering and Plant Propagation,” TR DS-78-16, Vicksburg, Miss., Dec. 1978. 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