From the baseline mapping and resulting contour maps, scenarios can be developed based on if the water rises, showing what is impacted and where excess water goes.The Great Lakes have had mood swings since their icy birth. Some days they are calm, their waters showing barely a ripple of blue satin. Other days they are angry, gray, and heaving. And they go through cycles of highs and lows that can last for years: Five years ago, for example, water levels were high and property owners were bemoaning beach losses; today, water levels are the lowest they’ve been in years (Lake Michigan is the lowest it’s been since 1964), and some Great Lakes shorelines are as wide as a football field. It’s just a matter of time before water levels inch up again, and before another major storm hits, and before the process of significant coastline erosion begins again. But this time, technology will help predict the impact of the lakes’ moods. USACE’s Detroit District has begun baseline mapping along the coastal zones of the Great Lakes and has hired Woolpert Design LLP to map a prototype area along the Lake Michigan shoreline using Light Detection and Ranging (LiDAR).LiDAR can be faster and less expensive than the photogrammetric process of collecting images and creating contours from aerial photography. Yet LiDAR is accurate: When integrated with an airborne global positioning system (GPS) and an inertial measurement unit, LiDAR can capture data with accuracies of 5-20 cm without supplemental GPS land surveys. This level of accuracy is important for future modeling efforts.In the four years that LiDAR has been used commercially, it has proven to be a good solution for shoreline mapping for which ground access can be difficult, setting targets might prove impossible because of the water, and viewing aerial photos stereoscopically might not be an option because the ebb and flow of waves means every photographic exposure is different.With LiDAR, as discussed in the “How LiDAR Works” sidebar, highly accurate digital elevation and digital terrain models can be generated immediately, before aerial photography is processed, ground control is acquired, and analytic triangulation is performed. Once analytic triangulation is finished, final edits and corrections can be done by photogrammetric methods. Integrating the LiDAR data with photogrammetric review often yields better results since shorelines frequently have heavy ground cover, and mapping goals are frequently 1- to 2-ft. contours. In other words, the combined LiDAR-photogrammetric compilation provides a more realistic depiction of the terrain than do LiDAR data alone, ensures desired map accuracies will be maintained, and offers a second means of quality control.A washout of a bluff along Lake Michigan.The devasting impact of recession and erosion on properties along the Lake Michigan coastFor these reasons, USACE chose LiDAR in combination with aerial photography for the baseline-mapping prototype project along the Lake Michigan coastline in Michigan’s Berrien and Allegan Counties. The project – which began in March 2001 and ended in November 2001 – established lake levels and land contours at specific points and places in time. The data will allow measurement of coastal recession and erosion based on registering archived photography as a sort of “what happened” scenario. Because the shoreline-to-bluff line was mapped in 3D, vertical-to-horizontal comparisons of the two lines and slope analysis can be made along the coast. These processes not only will enable users to see what erosion has done over time but also will aid in predictions of potential damages to natural and manmade features in the event of a major storm.The methodologies developed by this prototype are being used by USACE for mapping the Great Lakes shorelines. This is no small feat: These shorelines are 30% longer than the combined Atlantic, Pacific, and Gulf Coasts of the mainland US. The result: Baseline mapping will help USACE compare past and future modeling strategies and make better land-use and coastal-zone preservation recommendations so that the Great Lakes region will be better prepared to deal with erosion. Background: Mapping Driven by Ongoing StudyThe quest for baseline maps of the Great Lakes coastal zone was born of the Lake Michigan Potential Damages Study (LMPDS). In October 1996, USACE and cooperating agencies initiated an extensive long-term assessment of potential shoreline damage over the next 50 years from fluctuating lake levels along Lake Michigan. This study is dedicated to meeting several of the recommendations from the 1986-1993 International Joint Commission Great Lakes Levels Reference Study.Specifically, the study recommended that the economic value of all shoreline interests be objectively assessed in terms of potential damages that could occur under differing hydrologic conditions or alternative management approaches to water-level controls. This approach differs from damage surveys conducted in the 1970s, which were limited to actual losses that occurred under a specific extreme lake-level condition. The Lake Michigan study is expected to look at potential damages that could occur if water levels continue within the ranges that they have exhibited over the last 120 years or so or whether they would be significantly higher or lower due to climatologic variability or alternative regulation strategies.The International Joint Commission study also had several other recommendations that the LMPDS is attempting to address. These include initiation of coastal erosion monitoring programs, updating of coastal process research, updating of land-use information, and developing effective public information programs.The objective of the LMPDS is to create a modeling procedure for estimating economic effects of lake-level changes and related social, environmental, and cultural consequences. Lake Michigan was chosen for the first study because it has severe erosion problems and was the most damaged lake during high-water periods of the 1970s and 1980s. The study will address all economic factors in the coastal zone surrounding Lake Michigan, including coastlines, embayments, and interconnected lake bodies and rivers directly affected by the ranges of water levels defined in the study. It is expected that the methodology developed for the Lake Michigan study will be applied to the other Great Lakes so that a consistent approach is taken to the basin as a whole. Many efforts undertaken for Lake Michigan will be directly applicable to other lakes and economies of scale and lead to basinwide analyses. In fact, several of the tasks outlined under the Lake Michigan study have been implemented for new analyses of Lake Ontario coastal erosion processes.Potential damages are being assessed for all affected shoreline interests, including residential property; commercial, industrial, and institutional facilities; manufacturing and shipping; retail and other commerce; parks and recreational facilities; commercial fishery; and recreational boating and sports fishery. Community-based impacts also are being evaluated, including those relating to tourism, water supply, wastewater treatment, dredging, channel maintenance, and structural protection. Finally, environmental effects of extreme fluctuations are being addressed, including impacts on fisheries, habitat diversity, endangered and threatened species, and archaeological and special natural features. Prototype Mapping in Berrien and Allegan CountiesIn this planimetric map, the blue line indicates the water’s edge, yellow is the toe of the bluff, and red is the top of the bluff. The map establishes a baseline to help make predictions about future recession and erosion levels along Lake Michigan.For the prototype project born of the LMPDS, Woolpert was tasked with establishing a baseline mapping of the entire coastal zone in Berrien County and portions of the coastal zone in Allegan County. A typical mission was 6 mi. long and consisted of 13 passes, with 30% overlap on each pass to ensure that sufficient data were collected. Aerial photographs were taken simultaneously. As the plane flew in parallel lines collecting swaths of digital data up and down the coastal zone, two kinds of features data were collected at 400-ft. scale:Coastal features within 300 m from shore, collected by topographic LiDAR. Edge-of-water and top- and toe-of-bluff points were collected to develop a digital elevation model and ultimately a digital terrain model (DTM) with 2-ft. contour intervals, which would provide the level of accuracy and density needed for future modeling efforts. The LiDAR data were filtered and enhanced with photogrammetrically digitized topographic break lines.Cultural features within 1,000 m from shore, collected by photogrammetric mapping from the aerial photography. Shoreline-protection attributes, such as sea walls, revetments, jetties, and groins, and other attributes, such as buildings, utilities infrastructure, transportation networks, and even trees and inland waterways, were collected for future use in a geographic information system (GIS) to support the goals of the LMPDS. Separately, underwater elevation data had been collected using bathymetric LiDAR, which records underwater features using a green band of light. Specifically, the Scanning Hydrographic Operational Airborne LiDAR Survey (SHOALS) system was used. (Owned and operated by the Joint Airborne LiDAR Bathymetry Technical Center of Expertise – a partnership between USACE-South Atlantic Division, USACE’s Engineer Research and Development Center, the Naval Meteorology and Oceanography Command, and the Naval Oceanographic Office – SHOALS is considered one of the most flexible tools for surveying shallow water.) During postprocessing, the topographic and bathymetric LiDAR data were merged, creating an elevation model from within the lake to the top of the bluff edge. This model can be compared to archived and future photos to show changes in the waterline and the effects of erosion and recession over time.Also during postprocessing, the aerial photos were scanned and converted to digital orthophotos with a 6-in.-per-pixel ground-sample distance. At this level of detail, one can still see trees, poles, manholes, catch basins, and so on. This detail was “extracted” to create a bare-earth terrain model. The combination of LiDAR and orthophotos enabled creation of:planimetric maps clearly delineating the water’s edge, the toe of the bluff, and the top of the bluff;planimetric maps and graphs showing predicted dry 50-year, average 50-year, and wet 50-year bluff recession and erosion lines;ortho and bluff data draped over merged SHOALS and topographic LiDAR elevation data;a merged elevation model showing ortho data, 2-ft. contours, and the top and toe of bluff;cross-sectional views depicting recession and erosion.This map shows merged SHOALS (bathymetric ) and topographic LiDAR data: a complete elevation dataset from under water to past the top of the bluff.There were some special considerations for this project. Woolpert centered the LiDAR shoreline flight slightly offshore as opposed to above land, enabling the LiDAR unit to collect data from the coastal side of bluffs – thus avoiding any shadows or “dead zones” created by the bluffs. This action also allowed the LiDAR system to better penetrate such vegetation as trees. Using aerial photography to enhance the LiDAR data saved time and effort compared to gathering the data in the more conventional approach with photogrammetry. This combined approach also increased the accuracy of the DTM. The LiDAR-produced DTM allowed stereo compilers to begin the topographic mapping process with “bare-earth” data in place. A photogrammetrist checked the LiDAR-generated DTM that was superimposed over the stereo images to ensure that the DTM was accurately positioned on the surface. (LiDAR measurements can show the difference between a treetop and a clearing, but these measurements alone might not be able to distinguish between the edge of pavement and a row of cars parked at the edge of the road, for example. A photogrammetrist, however, can easily make such distinctions visually and correct the LiDAR data if necessary.)For the prototype project, Woolpert developed and enhanced the computer-aided drafting design (CADD) specifications table used by the USACE and branches of the US military. The table includes specifications for recording the detail of a number of features ultimately used in mapping, including buildings and structures; roadways and railroads; vegetation; storm and water structures; contours and spot elevations; poles, towers, signs, and posts; and political boundaries. Woolpert and USACE-Detroit District developed additional subfeatures under these headings that previously had not existed in the Tri-Service A/E/C CADD Standard. For example, under the “storm and water structures” heading, the following subfeatures were suggested: groin centerline, levee centerline, sea wall centerline, jetty outline, revetment outline, breakwater centerline, boat ramp outline, and ad-hoc shore features. These new features have been submitted to the CADD/GIS Technology Center (operated by the US Army Engineer Research and Development Center) to be permanently incorporated into the A/E/C CADD Standard.Applications of Coastal-Zone MappingAn orthophoto is draped over merged elevation data to produce this composite map. Buildings are indicated in red to show proximity to areas of potential recession and erosion.The applications of baseline coastal-zone mapping are varied and continue to evolve as more portions of the Great Lakes shoreline are mapped. The following is a general list of applications:Erosion Process Modeling and Assessment of Potential Damages. Damages to all land-use categories caused by erosion over the 50-year planning horizon can be calculated using baseline mapping and contour maps. Modeling will be coupled with a GIS to assess the economic and environmental implications of hydrologic scenarios that are significantly different from those of recent years. Specifically, an erosion processes model will be developed for describing erosion associated with cohesive and sandy shore conditions of the Great Lakes. Model development will include linking existing numerical models (wave climate, wave propagation, nearshore erosion process, and bluff failure) and making modifications to produce a versatile model for describing and predicting erosion for short- to long-term time scales. The model will be tested at select study sites and applied basinwide across the Lake Michigan shoreline to estimate the degree that beach erosion and bluff recession would be expected to take place in response to various hydrologic and control scenarios over the planning horizon of the study. The principal product will be an operational erosion process model that can simulate anticipated beach erosion and bluff recession rates under a variety of lake-level and storm-frequency scenarios. This model is designed to run at a local level so that county planners and community developers can anticipate likely changes in hazard zones along the shoreline. Also, the rate and location of bluff-line recession will help determine the number and type of parcels that will be affected by erosion over the 50-year period. Erosion impacts could include but are not limited to loss of property and structures within the bluff-line recession zone and costs of maintenance and repair to shore protection structures. Preliminary damage assessments were completed for Allegan County. Work continues on the remaining prototype counties.Land-Use Investigations. Orthophotos and planimetric maps can help planners differentiate residential and commercial uses and assess alternative land-use management options. This task will evaluate likely changes in land-use management practices as a direct or indirect consequence of changing conditions that could occur under the alternative hydrologic scenarios. Water-Level Scenarios and Flood-Elevation Modeling. The mapping can help predict water scenarios at dry 50-year, average 50-year, and wet 50-year periods, showing potential flooding and low-water impacts on river mouths. From the baseline mapping and resulting contour maps, scenarios can be developed based on whether the water rises, showing what areas and structures are affected and where excess water goes. USACE will use the maps to calculate damages to land under varying flooding conditions. USACE also can calculate damages for a minimum of two water levels above the riverbank of inland harbor areas (e.g., 100-year and 500-year water levels). Impacts of flooding could include, but are not limited to, loss of structures, loss of commercial income, and costs to communities and private citizens for cleanup and restoration of property. LiDAR surveys of three river mouths in the Michigan prototype counties were conducted, providing the basis for calculating flooding damages.Additionally, coastal-zone mapping could aid in coastal sand management; revegetation policies; dredging and channel maintenance; building setback polices; potential relocation of dwellings; shore alteration permitting; habitat regulations, including wetlands policies; public infrastructure controls and zoning policies; and incentives and disincentives, such as grants, loans, insurance, and deed restrictions and disclosures.The latest information on the LMPDS and USACE’s Great Lakes shoreline task activities is available at www.lre.usace.army.mil/index.cfm?chn_id=1134. ConclusionSince the Great Lakes were born some 10,000 years ago, they’ve given and they’ve taken. This cycle of erosion has only been anecdotally predictable – until now. Using LiDAR and other technologies, the Great Lakes shorelines are being mapped, providing baseline information that will be used not only to predict the potential damages to natural and manmade features caused by erosion, but also to help planners make better land-use and coastal-zone preservation recommendations. Erosion is inevitable, but humankind’s ability to deal with it has improved.
