Ohio Coastal Design Manual
|Chapter 1 |
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Promote better projects along the coast that balance the use of Lake Erie as a shared natural resource along with the property owners’ need for lakefront erosion protection and the benefit of access to the lake.
Chapter 1 describes the types of site-specific information that are usually needed by the engineer or surveyor in the development of a successful design for a project along the Lake Erie shore.
Most of the information described here would be incorporated into design drawings and submittals to the regulatory agencies that issue authorizations. Most of the information is readily available from county recorder’s and auditor’s offices, on-line sources, site inspections, the property owner and, in some cases, the ODNR Office of Coastal Management (OCM).
The sections of this chapter note why each type of information is important to the planning and design of a project and highlights conditions at a site that may impact the success of a design.
General vicinity map
A map showing the general location of the project is needed by the regulatory agencies and the public so that the project can be easily located. It also provides a larger frame of reference for the project and is used as a means of identifying nearby areas that may impact or be impacted by the project. Maps from on-line resources or maps from county auditor web sites are usually sufficient. It has also been common to use copies of a United States Geological Survey 7.5-minute topographical map, also known as a “quad” map. (top)
Identification of adjoining and nearby property owners
The agencies that authorize projects along Ohio’s Lake Erie coast are required to notify the property owners adjacent to the proposed work, and to request comments on the project. The names and addresses (both property and mailing) of all owners of properties that abut, adjoin or are adjacent to the project property along the lake shore must be identified. (top)
Each county auditor maintains this information and it is available through their web sites. In some cases, there may be multiple owners, or ownership associations that hold adjacent property. Subdivision plats, parcel deeds and association agreements should also be obtained and reviewed to identify the names and addresses of those with an interest in the property. All persons with an ownership or non-possessing interest, (such as an easement or a reservation of rights of way) in an adjacent property must be identified so that regulatory agencies can provide notice of the project.
History of the site
Historical information allows the designer or the surveyor to visualize how and why the shore at the project site has changed over time. Aerial and site photos from past years as well as recent photos may be available from sources such as online mapping services, county auditors and the OCM. A property owner may also have photos and information about when human-made site features were constructed. (top)
Regulatory agencies may have information related to project sites that have previously applied for or obtained authorizations. Site information that may be available includes authorization application forms, existing and proposed plans and section drawings, design assumptions and calculations, subdivision plats, parcel deeds, metes and bounds descriptions, submerged lands lease agreements and authorized permits. In some cases design information from adjacent properties may be available and may contain appropriate information for developing plans for a proposed project.
Site conditions and existing structures
The engineer should coordinate with a surveyor to conduct a field survey of the project area. All existing structures along the shore should be properly defined in location, elevation and dimension including retaining walls, decks and other upland structures at least up to the elevation where no erosion is present or anticipated. Survey the features that may affect design choices. Particular attention should be paid to rubble material located offshore and to adjacent structures. These may influence the wave climate and movement of littoral material, or interfere with watercraft access at the project site.
Development of a field survey by a PS is further discussed in Chapter 2.
A site plan, field notes and photographs documenting the current condition and composition of site features will aid development of the engineering design and drawings, as well as facilitate the permitting process. (top)
Coastal Erosion Area designation & erosion at the site
The ODNR Division of Geological Survey delineates the boundary of Ohio’s Coastal Erosion Area (CEA). The mapping program produces maps and tabulated datasets for Ohio’s entire Lake Erie shore. For these maps, erosion is measured at transects located approximately every 100 feet and a CEA boundary line is determined. The CEA boundary line represents the estimated location of the edge of the bluff or recession feature after 30 years. The maps and datasets, available from OCM upon request, are useful in establishing the historical rate of erosion at a project site and offer some indication of a site’s history.
The original CEA mapping, completed in 1998, was based on changes from 1973 to 1990 as determined from aerial photography. The CEA designation is periodically updated with the most recent designation released in 2010. This delineation was based on the changes from 1990 to 2004. (top)
Geology of the upland
Identifying the specific geology at a project site is critical. The type of materials present at the bluff face and beneath the surface is the single most important upland site condition. In general, most of the bluffs along the shore are comprised of bedrock overlain by one or more layers of a glacial till or glacial lake deposit, over which is usually a fill or top soil. In some areas the bedrock is exposed above lake level, as is the case along much of Cuyahoga County into eastern Lorain County where shale bluffs dominate. In other areas, the bedrock is below lake level, and the exposed bluffs are comprised of glacial tills and lake deposits.
The bedrock from Erie County east to Ashtabula County is shale, which is exposed along the shore of many reaches, most notably west of downtown Cleveland. The bedrock west of Sandusky is limestone, most visible along the west side of Catawba and the Erie Islands. West of Catawba, the shore is low-lying and composed mostly of recent sediment, sand and fill.
The glacial tills and lake deposits that overlay the bedrock are highly variable both in profile at a site and within short distances (even within 100 feet) along reaches of the shore. Glacial tills can range from very dense and nearly impermeable (the typical grey tills usually above the bedrock) to lighter clay-silt material with pockets of gravel. Lake deposit materials are also highly variable, ranging from clay-silts to very permeable sandy clays, the latter of which is a common upper stratum in much of Ashtabula County.
There are stretches (or reaches) along the shore that may appear to have consistent bedrock and overlying tills that can also include buried river beds or former stream channels. In these locations the bedrock, even offshore, may have eroded to elevations much deeper than the nearby area. These areas generally have less steep slopes along the lake and may contain existing streams and outlets to the lake.
The elevations of geologic strata boundaries should be identified. This is important if groundwater seeps are present along the bluff or if geotechnical engineering analysis is required to design a foundation or slope stabilization structure. The geological materials (or fill) should be defined so that they can be shown on a cross-sectional view of the existing bluff or slope with the associated elevations of each stratum.
There can be a number of distinct layers within each shale, limestone or glacial till unit along the shore with different physical and engineering properties. The engineer should evaluate whether the different properties within a bedrock or till have an impact on the design.
Examples of the importance of identifying and evaluating differences in the upland geology include:
- Sites with sandy, porous soils lying over dense glacial till are especially subject to upland slope failures caused by groundwater seepage weakening the resistance to slipping at the boundary between the two strata. Sites with this condition are found in Ashtabula County and parts of Lake County.
- Sites without exposed bedrock that have glacial till bluffs to the lake water level can experience high rates of wave-based erosion of the toe of the bluff. Following loss of a portion of the toe, the upland will be subject to slumping failures. This condition occurs in parts of Erie, Lorain and Lake counties and much of Ashtabula County.
- Sites with bedrock at the bluff face and above the elevation of the shore generally are less susceptible to wave-based erosion. This occurs in Cuyahoga and eastern Lorain County and the Lake Erie Islands area.
Identification of the geology and the engineering properties of the geologic strata present at the site are also critical in evaluating foundation loads, slope stability and the calculation of lateral earth pressures for any proposed structure near or on a bluff or bank.
Learn more online: Download Chapter 10: Geology of the Ohio Coastal Atlas Second Edition (top)
The lake would seem a natural sink for the storm water collected from roofs and paved areas. Nearly all lakefront property slopes toward the lake due to thousands of years of erosion.
In many of the geological settings along the lake, surface drainage and subsurface groundwater flow are the dominant forces influencing erosion of the upland. Existing surface drainage features that may need to be modified or re-routed as part of a shore structure project should be included in the design plan.
During site inspections, any visible indications of surface water run-off or groundwater problems should be located and described. Surface water run-off and groundwater seepage can cause erosion of the fill or existing bluff/bank material behind an erosion control structure which creates voids that may result in partial collapse of a section of the structure. Site conditions that indicate potential surface water or groundwater problems include:
- Gullies running down the bluff slope sides.
- Evidence of slumps along the bluff face.
- Ponded surface water on the flat upland.
- Areas of subsidence.
- Seeps along the bluff.
- Drain pipes extending over the bluff edge.
- Algae or wetlands vegetation along the bluff slope above the elevation of wave action.
- Channeling under soils, vegetation or fill material on the slope.
Characteristics of the shore
In order to understand how a project may impact adjoining and nearby properties, the characteristics of the shore along the area of the project site should be documented. Many features can be identified during site investigations including:
- The approximate width of the beach area.
- Approximate slope or profile of the beach and presence of terraced areas or wind-borne sand.
- Structures within the beach (pre-cast concrete modules, rubble, etc.).
- The size of the beach materials (sand, gravel, cobbles).
- The shape of the beach.
- Length of the beach overall as it extends over adjacent properties.
- Taking samples of the existing beach material during site investigations to be used for particle size analysis is strongly recommended.
The above information will represent the shore characteristics only at a single point in time. In many cases the property owner will have good anecdotal evidence and photographs of how the shore has changed over seasons and years.
Historical aerial photography can also be used to gain an understanding of how and why the shore has changed over time. When interpreting multiple aerial photos of a site, the designer needs to consider the differences in the lake’s water level elevation from one photo to another. NOAAs Tides and Currents website at www.tidesandcurrents.noaa.gov/station_retrieve provides historical water level elevation data for a number of locations on Lake Erie. (top)
Types of coastal habitats
Structures placed along the shore have impacts on the habitat available for flora and fauna. There are three general habitats present: nearshore, beach and upland.
The nearshore habitat extends from where the water meets the land (the swash zone) lakeward until the water is deep enough to be less affected by wave action. On Lake Erie, this would nominally be deeper than 20 feet. The nearshore area along the entire Ohio Lake Erie shore is vital to a healthy sport and commercial fishery, providing spawning, nursery and feeding areas for forage fish as well as for steelhead, bass, perch and walleye. (top)
The nearshore area is generally more productive than deeper areas of the lake, supporting significant populations of both phytoplankton and zooplankton which form the base of the lake’s food web. The nearshore habitat is differentiated by the type of material present along the bottom (the substrate). Rocky nearshore areas are favored by different species of fish and invertebrates than muddy or sandy areas. Nearshore habitats that support submerged aquatic vegetation (eel grass, for example) are rare in areas with deeper water or that are subject to significant wave action.
The beach habitat is landward of the water and is comprised mostly of material that is transported onto and off of the beach by wave action or wind. The lake’s beach habitats support distinct plant populations, some of which are rare. The beach also serves as a nexus where the food material generated by the lake can be accessed by birds and other land-based fauna. The beach habitat is highly valued and frequently visited by people. (top)
The upland habitat varies considerably along the Lake Erie shore from high bluffs to low wetlands all of which are distinct in their characteristics and the diversity of life they support. Although the Lake Erie shore is highly developed, even thin margins of bluff between the beach and the more level upper land can support diverse populations of plants and animals. Vegetation along bluffs, especially native trees and shrubs, provides critical habitat and food for resident and migratory birds. (top)
The effects of losing portions of one or more of the coastal habitats from one project at one property are apparently small, but the cumulative effect of structures along 80 percent of Ohio’s Lake Erie coast have been significant, though not yet fully appreciated or documented.
Coastal habitat-related issues that may have a direct impact on the design and construction of shore structures include:
- A prohibition on in-water construction at all locations, typically from April 15 thru June 30 to allow undisturbed fish spawning along the nearshore.
- All construction along or near the shores of Ohio’s Lake Erie Islands must be conducted after the hibernation period of the Lake Erie Water Snake has ended in the spring and before it begins in the fall. Work must be monitored and performed according to plans developed by the U.S. Fish & Wildlife Service.
- Projects adjacent to bald eagle nesting sites may have time periods during the hatching and fledging season when no construction can be performed.
Information about habitats and known locations of rare, threatened or endangered species is available from a number of sources including the online Ohio Biodiversity Database (formerly known as the Natural Heritage Database) maintained by the ODNR at www.ohiodnr.com/tabid/2010/Default.aspx. An endangered species review is performed by ODNR and the U.S. Fish and Wildlife Service as part of all Lake Erie projects that require authorizations from the U.S. Army Corps of Engineers and Ohio EPA.
Sites that have existing and stable beaches and diverse, well-vegetated, stable bluffs that support both nearshore fauna and coastal flora are among the most fortunate of all. To minimize impacts to coastal habitats, a “low-impact” design that leaves most of the existing beach and slope intact and still reduces long term erosion and provides access is an appropriate design choice.
Other site habitat information that might impact the design of a project can often be identified by the engineer or property owner during a site visit.
Learn more online: Download Chapter 7: Habitat of the Ohio Coastal Atlas Second Edition
Nearshore lake bottom elevations should be field-surveyed for all projects. The nearshore bathymetry (the measurement of water depths) is required to:
- Calculate the slope of the near-shore area.
- Establish the design depth of water at the proposed structures.
- Evaluate the wave climate (wave heights and directions).
- Evaluate the water depths and identify potential obstructions for watercraft use.
- Evaluate the potential changes to the movement of sand and gravel in the littoral system.
In most cases, measurement should begin at the crest of the beach and extend at least 100 feet from the anticipated location of the lakeward extent of the project. Bathymetric surveys are typically performed from the beach and by means of small watercraft. Common practice is to establish multiple transect lines along the shore and record elevations using land-based survey instruments. Bathymetric elevations should be referenced to the International Great Lakes Datum 1985 (IGLD 1985) which is discussed in Chapter 2. Using best surveying practices, elevations recorded at an accuracy of ± 0.2 foot are sufficient, given the changing nature of the water surface and the near-shore bottom.
It is also possible to obtain suitable bathymetric elevations by measuring the depth of water under calm conditions. The measured water depth can be referenced to the recorded water level data from the nearest NOAA water level gauge station. Water level stations in Ohio are at Toledo, Marblehead, Cleveland and Fairport Harbor. Data can be accessed for these locations online at:
The water level data from these gauges is reported relative to IGLD 1985. This method has the benefit of not requiring an on-land survey instrument beyond establishing the location of transect starting points and bearings.
Hand-held GPS units can be used to establish coordinates for the depth measurements, but care must be taken to incorporate the varying range of accuracy these units typically provide into final survey information. Due to the low level of precision and accuracy of hand-held GPS units, elevation readings obtained from this type of equipment are not suitable for bathymetric surveys.
The field survey should identify the substrates (bedrock, cobbles, sand, mud, etc.) present and any submerged off-shore structure such as stone, rubble, relict groins and piers. This information should be included on design drawings.
Navigation charts can be very helpful in understanding the larger scale, off-shore bathymetry and the effect on wave development. However, such charts are typically limited to 6-foot contour intervals with a few intermediate point depth measurements. These charts are not considered sufficiently accurate in depth or location along the shore to be used for design of shore structures. (top)
Performance of nearby structures
Existing structures adjacent to and near the project site can influence how a design performs and in turn can be affected by the proposed structure. During site investigations, the condition of nearby structures should be documented. For example:
- Does stone or rubble appear displaced? If so, what size is it?
- Are vertical seawalls or sheet pile structures leaning lakeward, undercut or washed out?
- Are crib structures dislocated, bending or emptying of rock fill?
- Are there major cracks in concrete structures?
Shore-perpendicular structures such as groins and piers will generally have a greater accumulation of littoral material (sand and gravel) on one side or the other. This is usually a good indication of the predominant direction of the movement of littoral material along a specific reach.
The condition of adjacent and nearby upland slopes should be noted. If adjacent property is receding, and erosion appears recent and ongoing, the edge of an erosion control structure at the project site may eventually be washed out or flanked if the design and arrangement of the structure does not adequately tie back into the slope. (top)
Site wave climate
The wave climate refers to the hourly, daily, seasonal or annual changes in wave height, period and direction. More generally, the wave climate is the expected range of winds and storms and their abilities to create elevated water levels and waves along the shore. Some project sites will be sheltered from waves from certain directions by nearby structures or the orientation of the shore. Other sites, especially around the islands and Sandusky Bay, may have a limited distance (or fetch) over which wind from a given direction can generate waves, limiting the wave height.
Many sites will experience full exposure to waves from winds and storms from the dominant southwest direction as well as the less frequent, but usually stronger, northeast storms.
Much the same as a wind rose, wave roses, as seen on this page, are used to evaluate the probability of wave height and direction and to assess the wave conditions that structures should be designed to withstand. The assessment of design wave heights for structures is discussed in detail in Chapter 3.
Observations at a project site under storm or high wind conditions can also be very helpful in developing a more visual understanding of the potential wave climate. It is useful to record the weather conditions and water level at the time of observation. Wind direction and velocity data are available online from sites including the NOAA Tides and Currents, NOAA Great Lakes Environmental Research Laboratory, the NOAA National Weather Service, and the nearest NOAA station on Lake Erie. (top)
Example Wave Rose
Station E008, NW of Avon Point. From the U.S. Army Corps of Engineers “WIS Report 22, Hindcast Wave Information for the Great Lakes: Lake Erie,” October 1991.
The numerical values at the end of each directional point are the percent of time waves will originate from that direction. The wave heights (in meters) are on a percent scale from the center of the rose. Looking at the SW direction, waves would come from the SW 23% of the time and of that, about 60 percent of those would be less than 1 meter in height. Note that this rose is for OFF-SHORE waves.
Potential waves heights in the nearshore can be calculated using this information (See Chapter 3).
Coastal Design Manual Online: