Wetland Mapping

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Written by charlie

Category: GIS & Mapping

Published: 17 May 2019

Created: 17 May 2019

Last Updated: 28 May 2019

After having some difficulty loading raster NOAA Nautical Charts into Grass Gis, I came across this page Converting NOAA raster charts to GeoTIFF for TileMill

I was not able to load the .KSP files for the NOAA rastermap (#12363- Long island Sound) into Grass GIS, with r.in.gldal despite its ability to handle .KSP files, but converting the files to GeoTIFFs first and then reprojecting worked perfectly. Determining the ESPG number was not readily apparent- as a workaround- I loaded the projection data (.prj) of an existing shapefile already existing in the Grass location into Prj2Epsg which returned a ESPG number of 4267.

1) Covert BSB to GeoTIFF

gdal_translate -of GTiff 12363.KAP 12363rectified.tif

 2) Reproject GeoTIFF into final file (12363rectified-reprojected.tif) using gdalwarp and the EPSG number

 gdalwarp -t_srs EPSG:4267 12363rectified.tif 12363rectified-reprojected.tif

 3) Load final file via Grass GUI as you normally would.

 The result is below- a NOAA rastermap overlain with vector bathymetric data (blue lines)

Details

Written by charlie

Category: Wetland Mapping

Published: 14 April 2016

Created: 14 April 2016

Last Updated: 15 August 2017

A comprehensive study of historical wetland losses between the 1880's and 2000's in the Long Island Sound, a 1,300 square mile estuary spanning the breadth of Long Island, New York City and up through Connecticut to Fishers Island was published this March by the Fish and Wildlife Service. The study is available here

The 31% loss of tidal wetland measured by the study mirror a common pattern of significant wetlands losses nationwide. Separately, Connecticut lost 27% of its coastal wetlands second to New York's 48% loss. Prior to 1970, wetland losses were largely a result of dredge and fill activities, which was sharply curtailed in 1970's with the passage of coastal wetlands laws protecting these valuable resources. The Connecticut Tidal Wetlands Act was passed in 1969.

The study was completed by scanning and georectifying old NOAA navigational charts dating back to the 1880's and comparing them against wetlands maps created during the last two decades. As expected, in some cases the margin of error is quite large. For many years wetland areas were only recorded as a byproduct of creating navigational charts, places to avoid running aground; they certainly were not mapped with the intention of measuring an important resource. Despite this, these maps still serve as an important, if not completely accurate, baseline depiction of wetlands.

Wetland losses can be broken into two groups, pre and post 1970. Prior to 1970, losses were largely conversion related. Losses after 1970 are less easily identifiable as being a result of a single practice, and appear to be a combination of multiple subtle stressors acting synergistically. These stressors include excessive nitrogen runoff, invasive species, sediment deprivation, changes in waterflow, pollution and climate change.

To illustrate this change, an average, healthy, unditched New England marsh is estimated to have 10% permanent open water. A recent Connecticut open water assessment determined that in the average wetland studied, 47% of it was considered permanent open water.

Ditching, a practice of digging a grid of ditches throughout a wetland to reduce its water level was a widespread practice throughout the East Coast and has hastened the conversion to open water. Networks of crisscrossing ditches were made in the early 20th century, frequently by hand, to combat mosquito borne diseases. Many of these ditches are still clearly visible and maintained throughout coastal Connecticut and Long Island. Since then, the efficacy of ditching to disrupt mosquito borne diseases has largely been discredited, and water levels are better managed through the use of tidal gates.

Today, the largest unditched tidal wetland in Connecticut measures 220 acres, is located in the Stratford Great Meadows part of the Stewart B. McKinney National Wildlife Refuge in Stratford, Connecticut.

To combat additional wetland losses a combined approach of addressing site-specific threats, and reaching out to the public to support large-scale conservation an d restoration projects could reduces wetland losses further in Long Island Sound.