David M. Bush

Utilization of geoindicators for rapid assessment of coastal-hazard risk and mitigation

Abstract Geoindicators provide a management tool for rapid assessment of natural hazard risk potential, either as a supplement to long-term environmental auditing and monitoring, or for initial coastal assessment as in developing countries. Using examples of barrier island and bluffed coasts, indicators of process/response are examined regionally, locally, and site-specifically; the latter being the primary indicators of property-threatening hazards. Tabled evaluation parameters range from general (elevation and vegetation) to specific characteristics such as shoreline stability and configuration, inlet proximity, and barrier-island interior geomorphology. Geoindicators also provide guidance for local mitigation of hazard impacts. A case study of Bogue Banks, North Carolina, shows that the geoindicators approach is applicable to communities with extant management plans. Bogue Banks’ five communities must reevaluate mitigation strategies after every storm and because of changes induced through development. By applying the geoindicators approach, shoreline reaches as well as interior areas may be reassigned as to the level of risk, and appropriate mitigation actions taken.

Application of the AMBUR R package for spatio-temporal analysis of shoreline change: Jekyll Island, Georgia, USA

The AMBUR (Analyzing Moving Boundaries Using R) package for the R software environment provides a collection of functions for assisting with analyzing and visualizing historical shoreline change. The package allows import and export of geospatial data in ESRI shapefile format, which is compatible with most commercial and open-source GIS software. The baseline and transect method is the primary technique used to quantify distances and rates of shoreline movement, and to detect classification changes across time. Along with the traditional perpendicular transect method, two new transect methods, near and filtered, assist with quantifying changes along curved shorelines that are problematic for perpendicular transect methods. Output from the analyses includes data tables, graphics, and geospatial data, which are useful in rapidly assessing trends and potential errors in the dataset. A forecasting function also allows the user to estimate the future location of the shoreline and store the results in a shapefile. Other utilities and tools provided in the package assist with preparing and manipulating geospatial data, error checking, and generating supporting graphics and shapefiles. The package can be customized to perform additional statistical, graphical, and geospatial functions, and, it is capable of analyzing the movement of any boundary (e.g., shorelines, glacier terminus, fire edge, and marine and terrestrial ecozones).

Comment [on “Sea level rise shown to drive coastal erosion”]

Leatherman et al. [2000] (Eos, Trans., AGU, February 8, 2000, p.55) affirm that global eustatic sea-level rise is driving coastal erosion. Furthermore, they argue that the long-term average rate of shoreline retreat is 150 times the rate of sea-level rise. This rate, they say, is more than a magnitude greater than would be expected from a simple response to sea-level rise through inundation of the shoreline. We agree that sea-level rise is the primary factor causing shoreline retreat in stable coastal areas.This is intuitive. We also believe, however, that the Leatherman et al. [2000] study has greatly underestimated the rate of coastal recession along most low slope shorelines. Slopes along the North Carolina continental shelf/coastal plain approach 10,000:1. To us, this suggests that we should expect rates of shoreline recession 10,000 times the rate of sea-level rise through simple inundation of the shoreline.

Hurricanes Gilbert and Hugo Send Powerful Messages for Coastal Development

Hurricanes Gilbert (8–19 September 1988) and Hugo (10–22 September 1989) are two of the largest and most destructive landfalling hurricanes in recent history. Differences in regional geography and type of coastal development, as well as storm size, track, and tidal stage at landfall had profound effects on the storm response of developed shorelines. In both the Yucatan Peninsula, Mexico (Gilbert) and South Carolina (Hugo), storm damage was increased by notching or removing dunes for development or beach access and by siting development at low elevations or ‘too close’ to the shoreline. High and wide dune fields, coastal forests, construction at high elevations, and building setbacks helped mitigate storm damage.

Documenting Beach Loss in Front of Seawalls in Puerto Rico: Pitfalls of Engineering a Small Island Nation Shore

The island of Puerto Rico is densely populated and heavily developed in some places, particularly along the shore and in coastal lowlands. Hard shoreline engineering is commonplace, even in low development density portions of the island. There are many examples of small trash revetments or cemented rock seawalls in front of individual buildings. In some cases, buildings themselves located within reach of waves and tides at the shoreline are behaving as seawalls too. Gabions have proliferated, even though they are decidedly not designed for either high-wave energy or salt-water usage.

GIS Applications in Coastal Property Risk Assessment

Many researchers have applied geographic information systems (CIS) to water-related problems, planning, mapping, and modeling, Application of GIS technology to hazard assessment and risk mapping along coastal areas, particularly barrier islands, will benefit the communities by providing a basis for zoning, land use planning, and allocation of resources for post-storm property reconstruction and pre-storm damage mitigation plans. GIS may also be used to map and assess damage and/or success of prior attempts to protect and preserve coastal resources so that damage mitigation procedures may be evaluated. Such applications of GIS may ultimately lead to quantified assessments of proposed construction sites with areas of high risk left in a natural state, thus saving money and, possibly, lives. An analysis of jekyll Island, Georgia (USA) using GIS technology was undertaken to assess the relative risk of property damage in a coastal area. This paper describes the general methodology behind coastal risk assessmen...

Impact of River Mouth Migration on Continental Margin Sedimentation: ABSTRACT

The migration of river mouths from one location to another on the high-energy, steep, narrow north shelf of Puerto Rico affects continental margin sedimentation in two major ways: (1) it results in vertical stacking of carbonate and terrigenous facies, and (2) it spreads sediment from small rivers over a large area. Additionally, it may explain the large number of submarine canyon tributaries that indent the shelf. River mouth migration thus appears to be a central factor of sedimentation in this dynamic, storm-dominated environment. Terrigenous sediment is introduced by small rivers only during storm-induced floods. This facies is characterized by dark, muddy, fine sand, mixed with a small percentage of continuously produced biogenic shelf carbonates. The terrigenous contribution forms thick pods of dark sediment directly off river mouths. This sediment contrasts with the thin veneer of light-colored carbonate sediment that slowly accumulates on shelf area away from river influence. In the Manati river pod, a small, extensively studied region of the north shelf, cores reveal an expected sediment sequence: coarse carbonate sand overlain by terrigenous material. Five kilometers away, in a separate sediment pod not presently adjacent to the active river, the inverse is true. In cores there, the lower unitmorexa0» is terrigenous sand and the upper unit is calcareous. This relationship is evidence of river mouth migration. The relict pod of river sediments has been gradually covered by biogenic shelf carbonates deposited since the Manati River mouth migrated to its present location.«xa0less

Computer-Assisted Prospect Generation in a Frontier Basin: ABSTRACT

Limited time and personnel resources often justify the utility and integration of computer techniques into exploration efforts in frontier basins. A large percentage of the exploration staffs of geologists and geophysicists have little comprehensive computer training. In addition, computer programmers and analysts have only limited experience using exploration data. To improve communication, it is often necessary to coordinate and cross-educate the two staffs. This enables computer applications to be used as an important tool by exploration personnel. Computer techniques were used by Pennzoil in the exploration and evaluation of the Santa Barbara channel basin in offshore southern California. Regional computer mapping including computer contouring located certain prospective areas permitting early concentration on the areas of interest. This effort resulted into the acquisition of Lease OCS P-0315 in Sale 48, June 1979. End_of_Article - Last_Page 555------------

Sedimentation on North Shelf of Puerto Rico: ABSTRACT

Regional sediment analyses along 100 km of the north shelf of Puerto Rico show the area to be a site of modern sedimentation. Sediments delivered to the steep, narrow, high-wave-energy north shelf by the Rio de la Plata, the Rio Grande de Manati, and the Rio Grande de Arecibo are in or approaching textural and compositional equilibrium with shelf processes. Modern sediments are being deposited over relict shelf sediments which are not in textural or compositional equilibrium. Relict and recent sands are easily distinguished by their contrasting color, composition, and texture. The river sands are predominantly dark colored and can contain a large percentage of mud. Upon entering the nearshore, they are entrained in the dominant westward littoral and shelf currents produced by persistent northeast trade winds. Minor eastward transport occurs partly as a result of an easterly component of tidal currents. Where terrigenous deposits are continuous between rivers, sediments sources have been delineated using X-ray diffraction of the heavy mineral suites. The relict calcareous shelf sands are predominantly light colored and of biogenic origin. They are occasionally isolated in nearshore shadow zones behind promontories or exposed in mid-shelf windows. Some mixing of relict and recent sands occurs immediately off the river mouths. The high wave-energy winnows the nearshore sands clean. Mid-shelf to basin transport of mud occurs in a series of storm-generated resuspensions. A low level of terrigenous contamination of carbonates indicates limited overlap between shelf sediment facies. Indeed, boundaries between sediment types are very sharp, often less than 200 m wide. This suggests localized controls on depositional processes. End_of_Article - Last_Page 908------------