Tangipahoa Crossing

PLANTING AND EROSION CONTROL TECHNIQUES IN A SCENIC LANDSCAPE

Associate Professor Dennis G. Abbey, ASLA

Louisiana State University

Baton Rouge, Louisiana 70803

February 1988

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"The goal of a properly designed bioengineered project has been reached when it no longer seems to be man made, but in fact appears to be the work of nature. This requires the skills of the engineer, the learning of the biologist, and the artistry of the landscape architect". (Schiechtl 1980)

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Abstract

This paper concerns itself with the role of the landscape architect, retained as a consultant, to plan, design and restore the banks of a scenic river that were severely damaged during pipeline construction. Illustration No. 1, Project Site, shows the point of convergence between the man made gas distribution system and nature's own drainage system. The site is located between Louisiana Highway 10 and Highway 16 in the sparsely populated town of Roseland, Louisiana just north of New Orleans, Louisiana. This paper acquaints the reader with the circumstances of the project which includes a cultural profile of Tangipahoa Parish, the natural profile of the general vicinity of the project site, and a design profile of the project.

Statement Of The Problem

Landscape Architects and The Rural Landscape

The American Society of Landscape Architects, (ASLA), adopted a Policy On The Rural Landscape in 1985 which embodies many of the principles landscape architects hold toward the land and which characterizes the profession of landscape architecture. The policy reflects the rural landscape as a "vital and productive qualitative resource" which recognizes the rural landscape as a "complex of ecological, economic and cultural qualities on which human and other life forms are dependent". The ASLA considers the continued misuse of the rural scenic or natural landscape threatening to present and future generations. (22)

Many landscape architects believe that the essential qualities of the natural and rural landscape can be conserved, while accommodating human needs, through the sensitive integration of human land uses, circulation systems, and structures with the natural systems of vegetation, soil, water, wildlife, and air. (4)

The landscape architect's impact upon rural planning and design issues is only now beginning to be appreciated. Their involvement with the rural issues of erosion control measures, sediment, control, stream bank preservation, and scenic rivers programs as well as utility system planning, design and construction is sure to be a growth area for landscape architecture in the future. In the area of pipeline planning and construction there is a demonstrated need to have landscape architects involved with all projects that traverse or encroach upon sensitive natural systems so that these man made systems become part of the sustainable landscape of America.

Illustration No. 1, Project Site

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Cultural Profile

History of The Site

The parish name of Tangipahoa is from the Indian tribe of the same name. Tangipahoa is variously translated to mean "ear of corn", "corn stalk", or "those who gather corn." The area of the parish (county), in which the project site is located is 803 square miles. The Parish is bordered on the north at North latitude 31 degrees by Amite and Pike County Mississippi and on the south at Pass Manchac on Lake Maurepas and Lake Pontchartrain. To the west is pastoral St. Helena, Parish, to the northeast is rural Washington Parish, and to the southeast, rapidly expanding New Orleans bedroom parish of St. Tammany.

Tangipahoa Parish, located near the center of the Florida Parishes, of Louisiana is a composite of most of the habitats typical of those parishes east of the Mississippi River with north-south trending rivers and streams. Prior to 1800, the region was sparsely populated. Dense forest of pine, oak, gum, ash, birch, holly, magnolia, poplar and cypress, lack of transportation and poor crop yields deterred settlers from migrating to the area. (21) Throughout the parish, from Greenlaw in the north to Lee Landing in the south, along the line of the Illinois Central railroad, are a number of 'hamlets", each containing at least one church, grocery store, gas station, school, restaurant, lounge and a fire station, polling booth or post office. (5) Illustration No. 2, Central Florida Parishes of Louisiana, after Cumley, shows the geographic distribution of the area.

People of Tangipahoa Parish

The cultural profile of Tangipahoa Parish is an interesting mixture of human characteristics. In the northern portion of the parish are found people with strong Anglo-Saxon Protestant heritage which can be traced to the upland hill regions to the east and northeast. In this region of piney woods, rugged individualism and upland south family traditions are the norm. Dairying and truck farming is the economic backbone of this section of the parish. Traditional ways are preserved and conservative attitudes toward change are common among the people. (21)

The southern portion of the parish in contrast is the most progressive and the most rapidly developing section of Tangipahoa Parish. This area hugging the swampy and marshy landscapes of Lakes Maurepas and Pontchartrain is populated by a people seeped in the general French cultural values of South Louisiana. These people, primarily French and Catholic, are rural and have a progressive spirit traced to the "joie de vive" of the Cajun life. A life in which Cajuns learned to live for the moment when living was good, and prayed and lit candles to Christ and the Virgin when times were bad. (26)

This area is rapidly developing into an urban industrial complex where commercial agriculture competes with business for economic supremacy.

In the middle of the parish, commonly referred to at the flatwoods, the economy rests upon productive family farms, small businesses which serve the farm community and light industry. Within this area is a large contingent of family oriented Italians and industrious Hungarians both with cultural ties to their native European homeland. Interspersed throughout the parish is a non-white population numbering approximately 31.6 percent.(23)

In recent years, the strawberry industry, recreation and tourism has played an important part in the economy of the parish. (10)

Use of The Tangipahoa River

The Tangipahoa River is suitable for multiple use as a recreation resource, therefore allowing such diverse activities as boating, fishing, hunting, hiking, trapping, wildlife studies, photography, bird watching, and general nature study. (19) Other uses include swimming and sun bathing, camping, visitor interpretation, and the most common use of the river, 'tubing'.

On selected weekends and holidays during the summer months one researcher studied usage on the river at a location just south of the project site. He estimates from his data that during the months of May to August

Illustration No. 2, Central Florida Parishes of Louisiana, after Cumley

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one would expect to find an average of 1401 users per day. (15) An earlier study (1978), over a typical summer weekend, counted more than 4500 users on four different stretches of the river in the vicinity of the site. (18) With usage such as this, it is no wonder that the stream segment fronting the site is included within Louisiana's scenic river system.

Scenic River System

Through legislative effort in protecting scenic streams, society has recognized its interdependence on the river and is "slowly evolving toward a symbiotic relationship, man and the river working together, for mutual benefit where man is the 'steward' of the resource". (2) Responding to this trend, the Louisiana Natural and Scenic Stream System Act, ( Act 398,La R.S> 56:1843), was passed by the Louisiana Legislature in 1970 with the general purpose of "preserving, protecting, developing, reclaiming and enhancing the wilderness qualities, scenic beauties and ecological regimen of certain free-flowing streams in Louisiana. (15)

By definition, a 'natural and scenic river' means "a river, stream or bayou segment thereof that is in a free flowing condition, that has not been channelized , cleared and snagged within the past twenty five years. Further, scenic streams have not been realigned, inundated, or otherwise altered and have shorelines covered by native vegetation with no or few man made structures." Included with the 50 streams so designated as scenic, is that segment of the Tangipahoa River from the Louisiana-Mississippi state line to the Interstate 12 crossing in which the pipeline crossing takes place.

Presently the program is administered by the Louisiana Department of Wildlife & Fisheries who under the Administrative Procedures Act, R.S. 49:950 et seq., make rules to implement the program. Their role, as administrator of the program, is to insure the general preservation of the river and to monitor prohibited uses such as channelization, clearing, snagging, channel realignment, reservoir construction and clearcutting within the so called 'related adjacent land' or 100 feet of the edge of the stream. Permits are required for certain uses, such as pipeline crossings,and civil penalty with fines may be assessed for violation of the law.

Small bluffs, up to 50 feet high, occur with regularity along the river giving great scenic beauty to the river environment. Illustration No. 3, Natural Character Near Project Site

NATURAL PROFILE

The River Environment

The Tangipahoa River, pronounced "tan ja pa ho" by natives has its headwaters in south Mississippi near Osyka, and flows due south across the Quaternary Lowlands of the Gulf Coast coastal plain approximately 50 miles until it falls into Lake Pontchartrain south of Ponchatoula, Louisiana. Several terraces with underlying sediments of unconsolidated Pleistocene and recent gravels, sands, silts and clays are present as a result of changes in sea level caused by glaciation and down-tilting of the Gulf Coast area.

The climate of Tangipahoa Parish is described as mild, humid and subtropical with an average temperature in January of 52 degrees and in July of 82 degrees. Annual rainfall at nearby Pine Grove, Louisiana averaged 66.22 inches of rain yearly over a 17 year period of study making this area the place of highest annual rainfall in the state. (1) The period of heaviest rain is in July and the least in October. Flash flooding of the river and nearby streams result with heavy rainfall. Minor rains in the region have great impact on the level of the river and flooding is a perpetual problem. One such rain, dropping four to seven inches up stream on February 1 & 2, 1988, caused a rapid 12.45 foot rise at the gage at Robert, Louisiana just south of the project site. Normal water elevation at this location is 6 feet above msl while flood stage is recorded at 13 feet. As a result of this minor flood, an estimated 12 feet of bank at the project site eroded away in 24 four hours in the first week of February 1988.

The course of the river is very active in its flood plain in response to the heavy floods and the unconsolidated nature of its bed. During the summer of 1987 the river was observed by the author to have changed its course over 15 feet in distance. The wild character of a river such as this makes it quite natural and very scenic and a focal point of recreational activity in the region.

Soil series near the project site are Ouachita, Ochlockonee and Guyton soils which are frequently flooded. (24) These loamy soils are gently undulating and strongly acidic at the surface. Specific soil samples taken from four locations on and adjacent to the project site show an average ph of 5.3, little or any organic matter except in one sample which had a content register of 3.15%, and deficiencies in nitrogen, phosphorus, potassium, calcium and magnesium. (29)

The potential for plant growth is poor. The main limitations are wetness, low fertility, and flooding hazard. (25)

Vegetation of The Region

The formation of the ridge and swale type of land in proximity to streams may be attributed to periodic bank flooding. The higher and dryer ridges have pine-oak communities of plants.(3) The vegetation of the sandy ridges and marshy depressions is preponderantly of the shrub and small tree type. The natural vegetation of the sandy ridges includes the dominants Illicium floridanum, Rhododendron canescens and the shrubby Simplocos tinctoria. Other native plants of the area include Crataegus spp., Acer rubrum, Quercus alba, Quercus lyrata, Quercus nigra, and Carya tomentosa. Chionanathus virginica and Oxydendrum arboreum are scattered with Cornus florida abundant on the more stable soils together with Rhus copallinum. (3)

Illustration no. 3, Natural

Character Near Project Site

Active components of the herb flora of the ridges include Ruellia parviflora, Arisaema quintum, Hexastylis arifolia and Dasystephana saponaria. Conspicuous because of color are Salvia coccinea, Salvia lyrata, Aster patens, Helenium nudiflorum and many species of Solidago. Brintonia discoides is prevalent everywhere.

The vegetation of the swales and shallow depressions is dominated by Asyrum stans, Ilex decidua and Ilex amelanchier.(3) The vegetation of Tangipahoa Parish can be broken down into three major forest groups.

Forested sites are further subdivided into the Longleaf Pine belt, the Flatwoods belt, and the Bottomland Hardwood and Cypress Forest belt along major streams, and the Cypress Forest belt near the edge of Lake Maurepas and Lake Pontchartrain. These natural vegetation regions parallel the gulf coast from north to south. (14) Illustration No. 4, Natural Vegetation Regions of Tangipahoa Parish, Louisiana

Illustration No. 4, Natural Vegetation Regions of Tangipahoa Parish, La.

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The Longleaf belt occurs in the north of the Parish where the topography presents some of the most interesting relief in Louisiana. Representative species of this belt include:

longleaf pine (Pinus palustris) slash pine (Pinus elliottii)

spruce pine (Pinus glabra) cypress (Taxodium distichum)

oak (Quercus marilandica) bitternut (Carya tomentosa)

honeysuckle (Lonicera spp.) huckleberry (Gaylussacia dumosa)

farkleberry (Vaccinium arboreum) native azalea (Azalea canescens)

Longleaf pine grows in open stands on the dryer sites of the Parish. Generally large spaces occur between individual trees. Spaces between are occupied by scattered groups of shrubs such as Myrica cerifera, Baccharis halimifolia, Ilex vomitoria, Vaccinium darrowii and Vaccinium arboreum. (1)

The Flatwoods belt has low relief and is nearly level with only slight undulations and topography broken by streams. The Flatwoods occur between the Longleaf Pine belt and the Cypress Forest (swamps) belt to the south. The distinct soils and internal drainage characteristics of the flatwoods have given rise to:

longleaf pine (Pinus palustris) loblolly pine (Pinus taeda)

southern red oak (Quercus rubra) scrub oak (Quercus ilicifolia)

black oak (Quercus velutina) willow oak (Quercus phellos)

water oak (Quercus nigra) swamp red maple (Acer rubrum var Drummondii)

green ash (Fraxinus pennsylvanica) magnolia (Magnolia grandifolia)

palmetto (Sabal minor) wiregrass (Spartina patens)

Associated species include most of the same species found in the Longleaf Pine belt with the addition of Ilex glabra, Cornus stricta and many species of Poaceae, Cyperaceae and Asteraceae. (1) Within low areas and depressions, plant species parallel those found in the Cypress Forest belt to the south.

On the slopes leading from the loblolly pine forests to the stream bottoms can be found one of the most interesting mixtures of plant materials to be found in the parish. Rich in diversity, texture and ornamental characteristics are such plants as Polystichum acrostichoides, Fagus grandifolia, Cornus florida, Tilia americana, Prunus serotina and Quercus shumardii. The floor of the slopes are covered with color throughout the year with such herbaceous plants as Viola spp., Hexastylis arifolia, Phlox divaricata. Uvularia perfoliata and Podophyllum peltatum. (1)

On stream bottoms are generally found the hardwoods and plants that colonize active sedimentation zones. Pinus taeda and Pinus glabra can sometimes be found along stream bottoms but most common plants include Halesia diptera, and Illicium floridanum. Other shrubs that will take occasional inundation include Viburnum dentatum, Sambucus canadensis, Itea virginica, Symplocos tinctoria, and the herbs Viola primulifolia, Poa autumnalis, and Polygonum spp..

Cypress forests occur along streams, in overflow areas and depressions and along the margins of the two lakes. Dominant species include:

bald cypress (Taxodium distichum) tupelo gum (Nyssa aquatica)

swamp maple (Acer rubrum drummondii) water oak (Quercus nigra)

bitternut hickory (Carya cordiformis) button bush (Cephalanthus occidentalis)

water ash (Fraxinus caroliniana)

Shrubs and herbaceous plants found associated with this landscape zone include Itea virginica, Ilex verticillata, Leucothoe racemosa, Onoclea sensibilis and Proserpinaca palustris. In areas of deep and prolonged flood and in active sedimentation zones one would expect to find the following plants:

cottonwood (Populus deltoides) sandbar willow (Salix interior)

southern catalpa (Catalpa bignoniodes) sycamore (Platanus occidentalis)

black willow (Salix nigra) sweet gum (Liquidambar styraciflua)

swamp privet (Forestiera acuminata) water locust (Gleditsia aquatica)

river birch (Betula nigra) blackberry (Rubus spp.)

Mention of the common plants may be of interest in that plants native to these environments are the early colonizers of the parish and relate directly to the design concept expressed below.

Design Profile

Design Concept

Water is one of the most powerful forces of nature, shaping the landscape, giving it character and providing contour and structure for the habitats of man, animal and plants.(17) Where water meets land there is constant flux and change. In Louisiana there are numerous zones in which water, land and man are in constant conflict, each trying to gain dominance over the other. In fact, one writer once said about Louisiana that "it is a place that seems often unable to make up its mind whether it will be earth or water, and so it compromises". (11) The result is that much of South Louisiana belongs to neither element and the line of demarcation between earth and water is vague and changing.

The river bank is the scene of the most dramatic interaction between water and land. Management of the water land conflict zone, the river bank, on the project site is the essential design problem. This problem is compounded by a crossing of an interstate pipeline system. Illustration No. 5, Site Restoration Master Plan, is used to guide the restoration project which followed the construction of a 30" gas pipeline crossing of the scenic river.

The 30" pipeline, part of an 1800 mile long duel pipeline system, is the sole supplier of natural gas to peninsular Florida. An existing 24" line, constructed in the 1950's, operated at near one hundred percent capacity during 1986 delivering 828 million cubic feet of natural gas a day to end users that included most of the state's electric utility companies. In order to serve a new contract for 345 million cubic feet of gas a day over fifteen years, with Florida Power & Light, the pipeline company began an expansion of the pipeline estimated to cost 188.5 million dollars. This expansion program consisted of adding a 30" line parallel to and at a greater depth than the existing line in order to increase the system capacity by 200 million cubic feet a day.

As the pipeline was dredged across the river the operations left denuded and exposed banks totaling 1600 linear feet that were out of character with the rest of the scenic qualities of the river. The banks were clearcut in the work areas of the pipeline crossing to a depth of approximately 630 feet. The south bank of the river, the cut bank, happened to be in the vicinity of an abandoned gravel pit and the site of the dredging operation. Due to the poor soil structure in this area it was eroding into the stream and causing turbidity downstream. Unconsolidated sands and gravels were at at the mercy of heavy and frequent rains in the area.

The master plan developed by the landscape architects, Abbey Associates, Inc. Baton Rouge, Louisiana organized all landscape construction and revegetation at the pipeline crossing following pipeline construction. The plan shows in a general way the types of work, grading, irrigation, erosion matting, and planting etc., involved with the restoration of the site.

Erosion Problem

During the preparation of the Site Restoration Master Plan a major design goal was placed upon the importance of high visual quality for canoeists and tubers. This was planned using native landscape features and materials and blending them in such a way that the crossing site would be un-noticed for recreationists floating south along the river.

Two types of erosion were identified during the planning phases of the project. Overland and rainfall erosion (type one erosion), were occurring as a result of the removal of the natural vegetation cover unconsolidated nature of the soils. Problems caused by type one erosion were limited to sedimentation into the river thereby raising turbidity levels downstream and a resultant public outcry. A more complex and dangerous type of erosion identified was involved with stream migration (type two erosion). This type going unchecked, would eventually remove the overburden of the 24" line which at one point within the work area was found to be 18" below grade.

Illustration No. 5, Site Restoration Master Plan

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Illustration No. 6, Alternative Erosion Devises, after GAI Consultants

The discussion below pertains to solving the problems of type one erosion overland flow and rainfall. To accomplish this goal of native character, it was determined at an early date in the design process by the landscape architects and clients that natural techniques (biotechnical engineering erosion control) would be used rather than structural devices to stabilize the banks of the river from overland and rainfall erosion, and restore them to a native character.

Biotechnical Site Engineering

This decision was based upon the following: Biotechnical engineering methods would be less expensive, easier and quicker to install, and would look better in the natural landscape. An additional factor considered was that the public wanted immediate effects while the pipeline company wanted all public attention on the matter dropped as quickly as possible. Illustration No. 6, Alternative Erosion Devises, after GAI Consultants , exhibits various erosion control devises that might be considered for projects such as this and their probable impact upon a range of shoreline activities.

The use of structural measures such as concrete and wood pile sills, turfblocks, gobimats, lokgards, fabric bags, grout-filled mattresses and concrete revetments, quarrystone gabions and structural bulkheads on a scenic river would be quite controversial. (6) In almost every instance, structural measures effect land use and the visual features and adds to the complexity and distortion of what are considered the three essential elements of a scenic stream. The elements of landform, vegetation pattern and water expression are essential for a quality river environment. (12)

Vegetation might be selected over the many structural and proprietary devices and specialty materials available for the prevention of erosion for several reasons. (13) Studies during the 1930's indicate biotechnical techniques provide for multiple-use of vegetation for wildlife habitat, natural beauty, slope stabilization, increasing groundwater infiltration, trapping wind blown sands, intercepting raindrops, retaining ground moisture and diminishing the rate of overland flow.(7)

Recent technical studies of biotechnical erosion control measures by Grey and Leiser, 1982, have examined the influence of vegetation on soil erosion. They found that foliage and leaf residues intercept rainfall, dissipate energy and increase surface roughness which slows the velocity of runoff. Root systems physically bind or restrain soil particles and both roots and residues increase infiltration by maintaining soil porosity and permeability. Finally they conclude that plants deplete soil moisture through transpiration giving the ground something of a sponge effect to allow it to absorb water. (9)

Other studies indicate that both live and dead plants can be useful in preventing erosion. (20) In the last few years it has become a widely accepted practice, for instance, to use such elements as erosion control blankets made of biologically inactive plant materials to slow the process of erosion. Erosion control blankets of organic matter are somewhat similar to 'brushmattresses' which have traditionally been used in Louisiana on streambanks for control of the land water conflict. In Louisiana, brushmattresses of willow (Salix nigra), have been used in the past to prevent levees from washing out during flood. Erosion blankets provide temporary cover for exposed soils and moderate the effects of rainfall impact, runoff velocity, and blowing winds. Erosion blankets are effective with type one erosion only.

Erosion control blankets are generally used to reduce soil erosion on slopes and to provide protective cover for seedbeds by moderating soil temperatures, reducing evaporative losses, and stabilizing seed locations until germination. (27) Often made of straw, wood excelsior, coconut fiber or synthetic materials fastened between layers of "biodegradable netting," erosion blankets are popular because of their 'unitized' format, ease of handling, and slow rate of decomposition. Although the blankets are of relative high cost as opposed to 'blowing straw,' studies have indicated that they are quite effective on roadside cuts, in drainage swales, and on open seeded areas all of which need to be stabilized following construction and removal of original vegetative cover. Reduction in soil loss of up to 99% over bare soil and reductions in water velocities of up to 78% are to be expected with the use of blankets.

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PLANT SPECIES SUITABLE FOR BIOTECHNICAL ENGINEERING IN SOUTH LOUISIANA

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maple (Acer) elm (Ulmus)

birch (Betula) barberry (Berberis)

ash (Fraxinus) dogwood (Cornus)

Ironwood (Carpinus) cotoneaster (Cotoneaster)

cherry (Prunus) sumac (Rhus)

poplar (Populus) hawthorn (Crataegus)

oak (Quarcus) privet (Ligustrum)

willow (Salix) rose (Rose)

honeysuckle (Lonicera) elderberry (Sambucus)

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Table No. 1, Plants Suitable For Biotechnical Engineering in South Louisiana

after Schiechtl 1980

Unitized blankets in four and six and one half foot widths, and covering areas of 60 to 80 square yards, are installed with prefabricated 9 or 11 gauge wire staples two to four feet on center over the area to be covered. The wire staples, six or eight inches long, are installed by hand or with a special device known as a 'gun'. Because of the ease of the installation of the units, blankets are very useful on steep slopes that are inaccessible to equipment and must be worked by hand. Illustration No. 7, Installed Unitized Erosion Blankets

Project Sequence

The first phase of the project planned between June and August of 1987 with construction commencing in September of 1987 was to cover some 1600 linear feet of river bank with blankets to prevent sediment erosion into the scenic stream while revegetation activities and re-grassing were taking place. Landscape construction activities during this phase included site preparation by shaping and grading of the river banks, seedbed construction and soil building, and seeding prior to the actual installation of the blankets.

A landscape barrier of 18" treated pine posts installed on 12" centers was designed to prevent the encroachment of recreational vehicles within the limit of work area. Soon thereafter, installation of an artificial irrigation system with quick coupling heads insured the survival of the germinating grass and ease of seedbed maintenance during the early growth stages of the emerging grass.

Following soil testing that indicated poor acidic soils, planting areas were improved by working into the top six inches of the site clean topsoil, organic matter, lime and fertilizers. Three types of grasses, to act as a cover crop were planted . Coastal bermuda (Cynodon dactylon) and annual ryegrass (Lolium perenne) were planted at an average depth of 1/4" while scarified Pensacola bahia grass (Paspalum notatum), was planted at a somewhat greater depth. Native wildflowers such as Scarlet flax, Painted daisy, Lanceleaved coreopsis, Black eyed susan, Cosmos, Chicory, and Indian blanket were hand seeded in specified areas to provide accent planting for the delight of the canoeing public.

Although the dominant species used for bioengineering were the native river birch (Betula nigra), and the colonizer willow (Salix nigra), other species of plants with similar suitability for biotechnical control were available. They are indicated in Table No. 1, Plants Suitable For Biotechnical Engineering in South Louisiana

Illustration No. 7, Installed Unitized Erosion Blankets

Illustration No. 8, Site Planting Concept Perspective

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Prior to placement of the blankets, areas for the construction of bioengineering features such as "slope facines," "cordons," and "tree islands" were considered for subsequent installation. These were designed to add to the length of the run to reduce overland flow and therefore reduce water velocities on the slope.

Brushmattresses, additional biotechnical erosion devices, were planned to be installed to help stabilize the banks from river rise flooding and to slow the current of the river during early spring rises in the vicinity of the bank. Slope facines of bundled willow cuttings averaged 24" wide and were spaced ten feet on the contour and perpendicular to the slope were also planned for the job. The placement of the facines slowed overland flow. Cordons were willow cuttings pegged in zig zag fashion up the slope to increase the length of run and thereby reduce the gradient of the runoff.

These erosion biotechnical control features were planned for placement on severe slopes with plant cuttings of native materials exhibiting adventitious root systems and a capacity to resist mechanical forces. Plants with the ability of the root system to consolidate and stabilize the soil with the added quality to develop sufficient tensile strength in the root system were sought.

Illustration No. 8, Site Planting Concept Perspective, shows the overall design scheme for the riverbank revegetation. The conceptual basis for the design rests upon the creation of 'tree islands'. The tree islands are representative natural features of the region and were conceived to be placed throughout the site in natural patterns simulating the effects of natural river processes.

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Illustration No. 9, Site Planting Concept

Tree islands are created naturally along the rivers of the Florida parishes. In this section of Louisiana, rivers are shallow with sandy, gravelly beds. As a result of the meandering of the river and deposition following the rise and fall of the river, a ridge and swale (accretion) topography results in the shoal area on the fill banks. (14) This natural process leads to the creation of islands which parallel the river. Because these islands are somewhat higher than their surroundings, pioneer species of vegetation find the opportunity to colonize.

On Thompson's and Alexander's Creek in West Feliciana Parish, the Amite River on the St. Helena Parish Line and on the Tangipahoa, these patterns of nature are very prevalent. Generally the initial colonizers of the ridges are black willow (Salix nigra), and river birch (Betula nigra), and their natural arrangement on the ridge is in a layered manner-oldest plants to the rear, youngest to the front.

Advantages of the tree island concept included the fact that the plantings could be used to slow runoff, stabilize the soil, direct, block and modulate views, as well as add native character to the site while at the same time concealing the row openings required above the buried pipelines.

A tree island exhibits a layered effect and illustrates the screenability of the planting. Plantings are in 'clusters' and typical islands on the site will have several species of trees ranging in size from bare root seedlings to 1 gal. and 5 gal. container plants. In addition, specimen trees in the 1"to 3" caliper range were planned to help stratify the layers. Native shrubs, to provide density to the screen, were added to the riverside of the tree plantings. 1

The islands parallel the river and are planted conceptually in ascending topographical order, from aquatics at the subaerial waters edge, through sandbank colonizers to bottomland hardwoods and terrace pines. Native bluffland hardwoods were planted at the top of the bluff. Illustration No. 9, Site Planting Concept, for the riverbank restoration.

In practice, this concept was limited by available plant materials in the trade and a knowledge of which plants might naturally restore themselves to the site. The design concept used in this project fits the need of restoring the site to its native character. Knowledge of which plants would thrive and be adaptable to the particular site, its soil, flooding characteristics, and human use requirements were instrumental to the success of this project.

Summary

Landscape architects serve an important function in fitting the built landscape and man made systems into the natural landscape. Their training in design, engineering, and biology can be useful to pipeline companies who must traverse sensitive landscapes such as scenic rivers. For maximum benefit to all parties involved with pipeline construction, the company, the landowner and the environment, the landscape architect must be involved with the project from an early date and must stay involved throughout construction and into the maintenance period.

At the time this paper was being written, the author has not had the time to evaluate long term effects. Time will tell how well the bioengineering erosion control measures worked to restore the riverbanks to the scenic river qualities that are characteristic of the Tangipahoa River in South Louisiana. The benefits of the landscape architect on projects such as the one described are only now being recognized. His most important function however is as his artistic eye for preserving and restoring nature and 'fitting in' the built works of man.

In the words of one old cajun pipeliner, "fo years, after we finish layin de pipe, we jus move' on. The idear of plantin de grass seed is new, hiring a landscape arch-a-tect to design is even newer. I don't believe de company ever hired a landscape arch-i-tect before now." (28)

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REFERENCES

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1) Allen, C., "A Flora of The Vascular Plants of St. Helena Parish, Louisiana", Louisiana State University Thesis, Baton Rouge, 1972

2) Benson, P., "Stewardship- Beyond Scenic Values to a River's Total Potential", Papers, 1977 Scenic Rivers Symposium, Louisiana State University, Baton Rouge, 1977

3) Bougere, L., "Vegetational Studies in Eastern St. Tammany Parish", Louisiana State University Thesis, Baton Rouge, 1953

4) Coen, D., Nassauer, J., Tutle, R., "Landscape Architecture In The Rural Landscape", Latis Series 10-American Society of Landscape Architects, Washington D.C., 1987

5) Cumley, J., "Hamlet Stability In The Florida Parishes Of Louisiana," Louisiana State University Thesis, Baton Rouge, 1986

6) GAI Consultants, "Low Cost Shore Protection/Guide For Engineers & Contractors", U.S. Army Corps of Engineers, Washington D.C., 1981

7) GAI Consultants, "Low Cost Shore Protection/Guide For Property Owners", U.S. Army Corps of Engineers, Washington D.C.,1981

8) Gayarre, C., "To Capitalists and Manufacturers", Illinois Central Railroad, New Orleans, n.d.

9) Gray, D., Leiser, A., "Biotechnical Slope Protection and Erosion Control", Van Nostrand Reinhold, New York, 1982

10) Hopper., A., "The Strawberry Industry In Louisiana," Louisiana State University Thesis, Baton Rouge, 1931

11) Kane, H., "The Bayous of Louisiana", Bonanza, New York, 1953

12) Litton, R. "River Landscape Quality and its assessment," Proceedings, River Recreation Management & Research, University of Minnesota-College of Forestry, Minneapolis, 1977

13) Lopez, S., "Coastal Design With Natural Processes", Latis Series 9-American Society of Landscape Architects, Washington D.C., 1985

14) Newton, M., "Atlas of Louisiana," School of Geoscience, Louisiana State University, Baton Rouge, 1972

15) Ochsner, S., "User Characteristics And Preferences on the Tangipahoa River, Louisiana", Louisiana State University Thesis, Baton Rouge, 1986

16) Palmer, T, "Wild and Scenic River Planning", Papers, 1977 Scenic Rivers Symposium, Louisiana State University, Baton Rouge, 1977

17) Rogers, Golden, Halpern, "Low Cost Shore Protection", U.S. Army Corps of Engineers, Washington D.C., 1981

18) Popadic, J., "Recreational Use of the Tangipahoa River, April 1977-1978." 1978

19) Popadic, J, Fannaly, M, Mclain, J. "Multiple Uses of Scenic Rivers ", Papers, 1977 Scenic Rivers Symposium, Louisiana State University, Baton Rouge, 1977

20) Schiechtl, H., "Bioengineering For Land Reclamation and Conservation," University of Alberta Press, Edmonton, Canada, 1980

21) Verret, M., "A Socio-Economic Profile of Tangipahoa Parish", Louisiana State University Thesis, Baton Rouge, 1966

22) __________, "ASLA Members Handbook," American Society of Landscape Architects, Washington D.C., 1986

23) __________, "Statistical Profile of Tangipahoa Parish," Public Affairs Research Council of Louisiana, Baton Rouge, 1973

24) __________, "Soils Report for Tangipahoa Parish, Louisiana," Soil Conservation Service, Alexandria , Louisiana, 1985

25) __________, "Soils Survey, East Baton Rouge Parish, Louisiana" Soil Conservation Service, 1968

26) Hollowell, C. "People of The Bayou" , Dutton Publications, New York, N.Y. , 1979

27) ______________ , "Nature's Blanket", North American Green, Evansville, IN, 1986

28) Thibodeaux, L. , " Personal Interview," Amite, Louisiana, 1987

29) _______________, Soils test, LSU Agronomy, 1987

Biography

Dennis G. 'Buck' Abbey, ASLA is Associate Professor of Landscape Architecture at LSU and a practicing landscape architect as Principal and C.E.O of Abbey Associates,Inc. Landscape Architects-Planners, Baton Rouge, Louisiana.

His education is strongly design oriented with degrees from Harvard, Michigan State and Jackson Community College.

Currently he is involved with a variety of professional master planning and site design projects with a number of landscape construction projects in various stages of completion. During 1987-88 he is exploring the relationship between landscape architecture and food culture as a NEA funded Louisiana State Arts Council Fellowship recipient.

Abbey is Secretary of the Louisiana Chapter of the American Society of Landscape Architects. He can be reached at (504) 388-1434 or 383-6078.

LIST OF ILLUSTRATIONS AND TABLES

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Illustration No. 1, Project Site

Illustration No. 2, Central Florida Parishes of Louisiana, after Cumley

Illustration No. 3, Natural Character Near Project Site

Illustration No. 4, Natural Vegetation Regions of Tangipahoa Parish, La.

Illustration No. 5, Site Restoration Master Plan

Illustration No. 6, Alternative Erosion Devises, after GAI Consultants

Illustration No. 7, Installed Unitized Erosion Blankets

Illustration No. 8, Site Planting Concept Perspective

Illustration No. 9, Site Planting Concept

Table No. 1, Plants Suitable For Biotechnical Engineering in South Louisiana

1 Due to changes in the construction schedule, this part of the project was delayed and had not been implemented while this paper was being written.

Tangipahoa Crossing

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