Shoreline change at Alaska coastal communities, Kotlik, Alaska

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Frequently anticipated questions:

What does this data set describe?

Title: Shoreline change at Alaska coastal communities, Kotlik, Alaska
Abstract:
The Division of Geological & Geophysical Surveys has analyzed long-term shoreline change at 48 Alaska communities. Shoreline datasets were compiled from previously published U.S. Geological Survey assessments and created from historical and recent aerial images by the Alaska Division of Geological & Geophysical Surveys. Shorelines were analyzed to calculate shoreline change rates every 25 meters along coastlines and tidally influenced riverbanks using the Digital Shoreline Analysis System (DSAS; Himmelstoss and others, 2018). The geodatabase for each community includes shoreline positions, the alongshore baseline used to cast transects, and transects that include shoreline change rates and statistics. All files can be downloaded free of charge from the Alaska Division of Geological & Geophysical Surveys website (http://doi.org/10.14509/30552).
Supplemental_Information: 
Baseline:    The Baseline line file gives the location of the alongshore baseline used to cast transects. 	
Rates:    Shoreline change is measured at regular intervals along the coast at transects that are cast orthogonal to shorelines from a baseline. Each method used to calculate shoreline change rates is based on measured differences between shoreline positions through time. The reported rates are expressed as meters of change along transects per year. When the user-selected rate-change calculations are processed, DSAS merges the individual module calculations, and the output is made available as a table in ArcMap. The rate-change statistics provided with DSAS have the standardized field headings. Some of the shoreline statistic values listed below require greater than 3 shoreline positions to calculate the statistic. If the shoreline statistic is a null value, there were not enough shorelines analyzed to compute that statistic.	
Shorelines:    Shoreline positions are a representation of a linear shoreline feature at a given point in time. These data were visually interpreted from historical and current orthorectified aerial photographs and delineated using ArcGIS.
  1. How might this data set be cited?
    Overbeck, J.R., Buzard, R.M., Turner, M.M., Miller, K.Y., and Glenn, R.J., 2020, Shoreline change at Alaska coastal communities, Kotlik, Alaska: Report of Investigation RI 2020-10, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 29 p., 47 sheets
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -163.578168
    East_Bounding_Coordinate: -163.474656
    North_Bounding_Coordinate: 63.049783
    South_Bounding_Coordinate: 63.019065
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 2020
    Currentness_Reference:
    ground condition
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: report, geodatabase
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a vector data set.
    2. What coordinate system is used to represent geographic features?
      Grid_Coordinate_System_Name: Universal Transverse Mercator
      Universal_Transverse_Mercator:
      UTM_Zone_Number: 3
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.999600
      Longitude_of_Central_Meridian: -165
      Latitude_of_Projection_Origin: 0
      False_Easting: 500000.000000
      False_Northing: 0
      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest .00000001
      Ordinates (y-coordinates) are specified to the nearest .00000001
      Planar coordinates are specified in Meters
  7. How does the data set describe geographic features?
    Baseline
    The Baseline line file gives the location of the alongshore baseline used to cast transects. (Source: DGGS)
    DSAS_ID
    Baseline identifier to determine the ordering sequence of transects. (Source: DGGS) Integer
    Rates
    Shoreline change is measured at regular intervals along the coast at transects that are cast orthogonal to shorelines from a baseline. Each method used to calculate shoreline change rates is based on measured differences between shoreline positions through time. The reported rates are expressed as meters of change along transects per year. When the user-selected rate-change calculations are processed, DSAS merges the individual module calculations, and the output is made available as a table in ArcMap. The rate-change statistics provided with DSAS have the standardized field headings. Some of the shoreline statistic values listed below require greater than 3 shoreline positions to calculate the statistic. If the shoreline statistic is a null value, there were not enough shorelines analyzed to compute that statistic. (Source: DGGS and Himmelstoss and others, 2018)
    TransectID
    The TransectID relates directly to the original transect file Object Identifier (Source: DGGS and Himmelstoss and others, 2018) Integer
    BaselineID
    Values in this field correlate to the baseline attribute field ID and are assigned by DSAS to identify the baseline segment used to generate the measurement transect. Baseline segments assigned an ID = 0 are ignored by DSAS, and no transects will be cast along those line segments. (Source: DGGS and Himmelstoss and others, 2018) Integer
    TransOrder
    Assigned by DSAS on the basis of transect order along the baseline or baselines. If the user manually adds transects to the file in an edit session, they will be added to the end of the transect attribute table and given a new value for TransID (ObjectID). However, TransOrder will be updated to reflect the position of the new transect with respect to the other transect along the baseline. As such, this field provides the user with a method to sort transect attribute data sequentially alongshore, from the start of the baseline segment with an ID=1 to the end of the final baseline segment. (Source: DGGS and Himmelstoss and others, 2018) Integer
    Azimuth
    Assigned by DSAS to record the azimuth of the transect measure in degrees clockwise from North. (Source: DGGS and Himmelstoss and others, 2018) Double
    ShrCount
    The total number of shorelines intersected by the transect and used for change analysis. (Source: DGGS and Himmelstoss and others, 2018) Integer
    TCD
    The TCD (total cumulative distance) is the measure (in meters) along the shore from the start of the baseline segment with an ID =1 and measured sequentially alongshore to the end of the final baseline segment. (Source: DGGS and Himmelstoss and others, 2018) Double
    SCE
    Shoreline change envelope; the "SCE" value represents the greatest distance among all the shorelines that intersect a given transect. The value for SCE is always positive. If the proxy-datum bias (PDB) is applied, two versions of this statistic will be reported: SCE will include the PDB in the calculations; NB_SCE will omit the PDB. (Source: DGGS and Himmelstoss and others, 2018) Double
    NSM
    Net shoreline movement (NSM) is the distance between the oldest and youngest shorelines at each transect. If the PDB is applied, two versions of this statistic will be reported: NSM will include the PDB in the calculations; NB_NSM will omit the PDB. (Source: DGGS and Himmelstoss and others, 2018) Double
    EPR
    The end point rate (EPR) is calculated by determining the distance between the oldest and youngest shoreline on a DSAS transect and dividing by the time elapsed between the two shoreline dates. If the PDB is applied, two versions of this statistic will be reported: EPRwill include the PDB in the calculations; NB_EPR will omit the PDB. (Source: DGGS and Himmelstoss and others, 2018) Double
    EPRunc
    An estimate of end point rate uncertainty. The shoreline uncertainties for the two positions used in the end point calculation are each squared, then added together (summation of squares). The square root of the summation of squares is divided by the number of years between the two shorelines. If the PDB is applied, two versions of this statistic will be reported: EPRunc will include the PDB in the calculations; NB_EPRunc will omit the PDB. (Source: DGGS and Himmelstoss and others, 2018) Double
    LRR
    A linear regression rate-of-change statistic was calculated by fitting a least-squares regression line to all shoreline points for a particular transect. The best-fit regression line is placed so that the sum of the squared residuals (determined by squaring the offset distance of each data point from the regression line and adding the squared residuals together) is minimized. The linear regression rate is the slope of the line. The rate is reported in meters per year, with positive values indicating accretion and negative values indicating erosion. If the PDB is applied, two versions of this statistic will be reported: LRR will include the PDB in the calculations; NB_LRR will not include the PDB. If the PDB is not applied, the LRR statistic will not include the bias. (Source: DGGS and Himmelstoss and others, 2018) Double
    LR2
    The R-squared statistic, or coefficient of determination, is the percentage of variance in the data that is explained by a regression. It is a dimensionless index that ranges from 1.0 to 0.0 and measures how successfully the best-fit line accounts for variation in the data. The smaller the variability of the residual values around the regression line relative to the overall variability, the better the prediction (and closer the R-squared value is to 1.0). If the PDB is applied, two versions of this statistic will be reported. LR2 will include the PDB; NB_LR2 will not include the PDB. (Source: DGGS and Himmelstoss and others, 2018) Double
    LSE
    The predicted (or estimated) values of y (the distance from baseline in meters) are computed for each shoreline point by using the values of x (the shoreline date) and solving the equation for the best-fit regression line (y=mx+b). The standard error is also called the standard deviation. This metric evaluates the accuracy of the best-fit regression line in predicting the position of a shoreline for a specific date. If the PDB is applied, two versions of this statistic will be reported. LSE will include the PDB; NB_LSE will omit the PDB. (Source: DGGS and Himmelstoss and others, 2018) Double
    LCI90
    The standard error of the slope with confidence interval describes the uncertainty of the reported rate for the user-selected confidence value captured as part of the attribute name. If the PDB is applied, two versions of this statistic will be reported. LCI90 will include the PDB; NB_LCI90 will omit the PDB. (Source: DGGS and Himmelstoss and others, 2018) Double
    WLR
    In a weighted linear regression (WLR), more reliable data are given greater emphasis or weight towards determining a best-fit line. In the computation of rate-of-change statistics for shorelines, greater emphasis is placed on data points for which the position uncertainty is smaller. If the PDB is applied, two versions of this statistic will be reported: WLR will include the PDB in the calculations: NB_WLR will not include the PDB. (Source: DGGS and Himmelstoss and others, 2018) Double
    WR2
    The R-squared statistic, or coefficient of determination, is the percentage of variance in the WLR that is explained by a regression.It is a dimensionless index that ranges from 1.0 to 0.0 and measures how successfully the best-fit line accounts for variation in the data. The smaller the variability of the residual values around the regression line relative to the overall variability, the better the prediction (and closer the R-squared value is to 1.0). If the PDB is applied, two versions of this statistic will be reported. WR2 will include the PDB; NB_WR2 will omit the PDB. (Source: DGGS and Himmelstoss and others, 2018) Double
    WSE
    The standard error of the estimate for the weighted linear regression rate. The standard error evaluates the accuracy of the best-fit regression line (WLR) in predicting the position of a shoreline for a specific date. If the PDB is applied, two versions of this statistic will be reported. WSE will include the PDB; NB_WSE will not include the PDB. (Source: DGGS and Himmelstoss and others, 2018) Double
    WCI90
    The standard error of the slope with confidence interval describes the uncertainty of the reported rate for the user-selected confidence value captured as part of the attribute name. If the PDB is applied, two versions of this statistic will be reported. WCI90 will include the PDB; NB_WCI90 will omit the PDB. (Source: DGGS and Himmelstoss and others, 2018) Double
    Shorelines
    Shoreline positions are a representation of a linear shoreline feature at a given point in time. These data were visually interpreted from historical and current orthorectified aerial photographs and delineated using ArcGIS. (Source: DGGS)
    Date
    The acquisition date of the imagery that was used to delineate shoreline position. (Source: DGGS) Date
    Uncertainty
    Root sum of squares of four uncertainty values associated with shoreline position, including positional uncertainty for ground control used to reference imagery, horizontal uncertainty associated with orthorectification distortions, spatial uncertainty dependent on imagery's spatial resolution, and uncertainty due to shoreline indicator interpretation during the digitization process. (Source: DGGS) Single
    SIndicator
    Shoreline indicator used to delineate shoreline position. (e.g., visible wet/dry line or vegetation line); VL = Vegetation Line, HWL = High Water Line, and LWI = land-water interface. (Source: DGGS) String
    Digitizer
    Name of the digitizer who delineated the shoreline. (Source: DGGS) String
    Agency
    Name of the agency that delineated the shoreline. (Source: DGGS) String
    Source
    Source agency or organization of the imagery used to delineate the shoreline position. (Source: DGGS) String

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
  2. Who also contributed to the data set?
    This work was funded by FEMA, the State of Alaska, the Denali Commission, and the U.S. Bureau of Indian Affairs. Data were produced by the Alaska Division of Geological & Geophysical Surveys, the U.S. Geological Survey, and the UAF Arctic Coastal Geoscience Lab.
  3. To whom should users address questions about the data?
    Alaska Division of Geological & Geophysical Surveys
    GIS Manager
    3354 College Rd
    Fairbanks, AK
    USA

    907-451-5020 (voice)
    dggsgis@alaska.gov
    Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays

Why was the data set created?

Many of Alaska's coastal communities are vulnerable to erosion, flooding, and permafrost degradation. However, there are few vulnerability assessment tools available to the public that are complete or that utilize transparent, consistent, and quantitative methods at a scale needed for local planning. This work is an effort to provide numerical shoreline change data to Alaskans for local decision-making and erosion vulnerability assessments.

How was the data set created?

  1. From what previous works were the data drawn?
    Boak, E.H. and Turner, I.L., 2005 (source 1 of 3)
    Boak, E.H., and Turner, I.L., 2005, Shoreline definition and detection - A review: Journal of Coastal Research v. 21, no. 4, Coastal Education & Research Foundation, Coconut Creek, FL.

    Online Links:

    • null

    Type_of_Source_Media: paper
    Source_Contribution: historical shoreline compilation
    Dolan, Robert and others, 1991 (source 2 of 3)
    Dolan, Robert, Fenster, M.S., and Holme, S.J., 1991, Temporal analysis of shoreline recession and accretion:: Journal of Coastal Research v. 7, no. 3, Coastal Education & Research Foundation, Coconut Creek, FL.

    Online Links:

    • null

    Type_of_Source_Media: paper
    Source_Contribution: historical shoreline compilation
    Himmelstoss, E.A. and others, 2018 (source 3 of 3)
    Himmelstoss, E.A., Farris, A.S., Henderson, R.E., Kratzmann, M.G., Ergul, Ayhan, Zhang, Ouya, Zichichi, J.L., and Thieler, E.R., 2018, Digital Shoreline Analysis System (DSAS) Version 5.0 User Guide: Open-File Report OF 2018-1179, U.S. Geological Survey, United States.

    Online Links:

    Other_Citation_Details: 110 p
    Type_of_Source_Media: ArcGIS extension
    Source_Contribution: historical shoreline compilation
  2. How were the data generated, processed, and modified?
    Date: 2020 (process 1 of 2)
    Historical shoreline compilation - Shoreline positions are compiled from previously published U.S. Geological Survey assessments as well as delineated from orthorectified historical and modern aerial imagery. The agency or organization that produced the imagery and shoreline vector are noted in the Shorelines data table. Data sources used in this process:
    • Boak, E.H. and Turner, I.L., 2005
    • Dolan, Robert and others, 1991
    • Himmelstoss, E.A. and others, 2018
    Date: 2020 (process 2 of 2)
    Projected shoreline positions - Shoreline change is measured at 25-meter alongshore transects that are cast orthogonal to shorelines from an offshore baseline. At each transect, DSAS marks the shoreline intersection position and measures the distance between shorelines through time to compute statistical rates of change.
  3. What similar or related data should the user be aware of?
    Overbeck, J.R., Hendricks, M.D., and Kinsman, N.E.M., 2016, Photogrammetric digital surface models and orthoimagery for 26 coastal communities of western Alaska: Raw Data File RDF 2016-1, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 3 p

How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?
    DGGS staff have performed a visual qualitative assessment of each shoreline file to ensure consistency between digitized lines and originating images. The accompanying delivery report provides additional information about the procedures used to determine uncertainty values for shoreline positions and shoreline change statistics.
  2. How accurate are the geographic locations?
    Shoreline positions are a representation of a linear shoreline feature at a given point in time. These data were visually interpreted from historical and current orthorectified aerial imagery and delineated in ArcGIS. Several factors have the potential to introduce positional uncertainty in the measured or interpreted results. These factors include horizontal uncertainty of the source imagery or ground control and the orthorectified image, spatial uncertainty associated with the imagery's spatial resolution, and uncertainty due to shoreline indicator interpretation during the digitization process. The accompanying delivery report provides additional information about the procedures used to determine uncertainty values for shoreline positions.
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
    Gaps in shoreline data and transect data may occur due to gaps in orthoimagery data, location and extent of coastal river channels or lakes, and infrastructure impeding the shoreline such as docks, revetments, and roadways.
  5. How consistent are the relationships among the observations, including topology?
    Not applicable.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints:
This report, map, and/or dataset is available directly from the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (see contact information below).
Use_Constraints:
Any hard copies or published datasets utilizing these datasets shall clearly indicate their source. If the user has modified the data in any way, the user is obligated to describe the types of modifications the user has made. The user specifically agrees not to misrepresent these datasets, nor to imply that changes made by the user were approved by the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys. The State of Alaska makes no express or implied warranties (including warranties for merchantability and fitness) with respect to the character, functions, or capabilities of the electronic data or products or their appropriateness for any user's purposes. In no event will the State of Alaska be liable for any incidental, indirect, special, consequential, or other damages suffered by the user or any other person or entity whether from the use of the electronic services or products or any failure thereof or otherwise. In no event will the State of Alaska's liability to the Requestor or anyone else exceed the fee paid for the electronic service or product.
  1. Who distributes the data set? (Distributor 1 of 1)
    State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys
    Attn: Simone Montayne
    3354 College Road
    Fairbanks, AK
    USA

    907-451-5020 (voice)
    907-451-5050 (FAX)
    dggspubs@alaska.gov
    Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays
    Contact_Instructions:
    Please view our website (http://www.dggs.alaska.gov) for the latest information on available data. Please contact us using the e-mail address provided above when possible.
  2. What's the catalog number I need to order this data set? RI 2020-10
  3. What legal disclaimers am I supposed to read?
    The State of Alaska makes no express or implied warranties (including warranties of merchantability and fitness) with respect to the character, function, or capabilities of the electronic services or products or their appropriateness for any user's purposes. In no event will the State of Alaska be liable for any incidental, indirect, special, consequential, or other damages suffered by the user or any other person or entity, whether from the use of the electronic services or products, any failure thereof, or otherwise, and in no event will the State of Alaska's liability to the requestor or anyone else exceed the fee paid for the electronic service or product.
  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 02-Mar-2021
Metadata author:
Simone Montayne
3354 College Road
Fairbanks, AK
USA

907-451-5020 (voice)
Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
Metadata extensions used:
Generated by mp version 2.9.50 on Wed Mar 03 12:32:14 2021