Description: Polygon feature class intended to provide a map link to Wetland or Watercourse Critical Area Studies, generally processed by the Planning Dept. as part of a CAO project.
Description: Polygon feature class intended to provide a map link to Wetland or Watercourse Critical Area Studies, generally processed by the Planning Dept. as part of a CAO project.
Description: Herrera developed a GIS-based model that overlays spatial datasets known to correlate with wetland presence to calculate the relative likelihood of wetlands on the ground. Six metrics were identified to be included in this analysis:1. Topographic Wetness Index (TWI): TWI is a measure of wetness based on LiDAR data. It is function of slope and contributing areas and assumes that concave, low gradient areas gather water while steep, convex areas shed water. TWI is highly correlated with soil moisture content and is frequently used as a metric in wetland identification analyses.Herrera calculated TWI for the City using 2016 LiDAR data with a 3-foot cell size. Values range from 0.18 to 27.4. Herrera considered anything greater than 6 as an area of high potential wetness.2. Topographic Position Index (TPI): TWI is a measure of the elevation change between a given grid cell and the average elevation of its immediate neighbors. Areas of topographic depression have been shown to be correlated with wetland presence because they are conducive to water pooling. Herrera calculated TPI using 2016 LiDAR data with a 3-foot cell size.3. Hydric Soil Status: Hydric soils are formed under conditions of saturation, flooding or ponding during the growing season such that anaerobic conditions develop. Hydric soil polygons were obtained from the Natural Resources Conservation Service (NRCS) and are classified as Not Hydric, Partially Hydric, and All Hydric.4. Landsat Dynamic Surface Water Extent (DSWE):The U.S. Geological Survey collects Landsat satellite data on a reoccurring basis that collects data on the existence and condition of surface water. This data product is a six-band raster dataset called the Dynamic Surface Water Extent (DSWE) with 30-meter pixels with each pixel being classified as either wet or not. Herrera obtained DSWE datasets collected in the rainy season (March) for 5 dates between 2010 and 2018 and calculated the number of times each pixel was wet. If a pixel is shown as wet multiple times, it is reasonable to assume a higher level of confidence of wetness at that location.5. Mapped Springs:The City of Mercer Island has mapped the locations of springs. Shallow groundwater has been observed at these locations which is a strong predictor of wetland presence. Herrera applied a 15-foot buffer to each mapped spring point or polyline for use in this analysis.After each metric was calculated, the following scoring matrix was applied at a 3-foot grid cell to dataset. The datasets were then overlaid together to obtain a cumulative wetland model score for each grid cell:GIS-Based Wetland Model Metrics and ScoringConveyance TypeMetricAttributeScoringTopographic Wetness IndexArea of high potential wetness (TWI > 6) 3Topographic Position IndexArea mapped as a depression3Hydric SoilsNot HydricPartially HydricAll Hydric1 2 3SpringArea located within 15 feet of a mapped spring2Landsat DSWEPixel not mapped as wet on any datePixel mapped as wet on 1-2 datesPixel mapped as wet on 3-4 datesPixel mapped as wet on all 5 dates0123
Copyright Text: Mercer Island, Herrera Environmental Consultants
Description: Polygons cover any point on the island where there exists another point within a 40 foot radius that has an elevation difference of more than 12 feet .Steps used to create feature class:1. Create grid of points, 4 foot on center, covering the entire island (approx 11 million records)2. Join elevation data to points from surface (2016 Geoterra Lidar)3. Create grid of 200 foot squares, each buffered 40 feet for overlap. (The script was failing when trying to process the entire island- broke up into smaller squares to be considered one at a time.)4. Run script in project folder, which selects a point, evaluates it against every point within 40 feet, and returns "1" if high slope condition is met, or "0" if not. (Script currently located in M:/ArcMap Documents/DSG/ForHolly/2019 Tree Slope Permit)5. Buffer "1" points, merge and smooth until it looks good (we weren't going for extreme accuracy)
Description: As defined in the City of Mercer Island's Comprehensive Plan under Shoreline Master Program Policies, Designated Environments. The purpose of the urban residential environment is to accommodate residential development and appurtenant structures that are consistent with this chapter. An additional purpose is to provide appropriate public access and recreational uses.Designation Criteria: Areas that are predominantly single-family or multifamily residential development or are planned and platted for residential development.Management Policies: (1)Standards for density or minimum frontage width, setbacks, lot coverage limitations, buffers, shoreline stabilization, vegetation conservation, critical area protection, and water quality should be set to assure no net loss of shoreline ecological functions, taking into account the environmental limitations and sensitivity of the shoreline area, the level of infrastructure and services available, and other comprehensive planning considerations.(2)Development of multifamily, recreational and residential subdivisions of five or more lots should provide public access and joint use for community recreational facilities, except when there are constitutional or other legal constraints.(3)Access, utilities, and public services should be available and adequate to serve existing needs and/or planned future development.(4)Non-commercial recreational areas should be allowed.
Copyright Text: City of Mercer Island Community & Planning Department & Information Geographic Services Team (GIS)
Description: As defined in the City of Mercer Island's Comprehensive Plan under Shoreline Master Program Policies, Designated Environments. The purpose of the urban park environment is to protect and restore ecological functions in urban and developed settings, while allowing public access and a variety of park and recreation uses.Designation Criteria: An urban park environment designation will be assigned to publicly owned shorelands, including all parks, street ends and public access points.Management Policies:(1)Uses that preserve the natural character of the area or promote preservation of open space, or sensitive lands either directly or over the long term should be the primary allowed uses. Uses that result in restoration of ecological functions should be allowed if the use is otherwise compatible with the purpose of the environment and the setting.(2)Standards should be established for shoreline stabilization measures, vegetation conservation, water quality, and shoreline modifications within the urban park designation. These standards should ensure that new development does not result in a net loss of shoreline ecological functions.(3)Public access and public recreation objectives should be implemented whenever feasible and significant ecological impacts can be mitigated.(4)Water-oriented uses should be given priority over nonwater-oriented uses. Water-dependent uses should be given highest priority.
Copyright Text: City of Mercer Island Community & Planning Department & Information Geographic Services Team (GIS)
Description: The Model Toxics Control Act (MTCA) governs the cleanup and prevention of contaminated sites that can threaten people's health and the environment in Washington State. Data for Mercer Island was downloaded as a CSV file from the Department of Ecology "What's In My Neighborhood?" website on January 22, 2018 and was converted to a GIS point shapefile based on latitude and longitude coordinates. It is important to note that these locations are approximate, and further verification should be done to make sure that each point is associated with the correct address.Site statuses include: Cleanup Started, Awaiting Cleanup, and No Further Action,More information about the Model Toxics Control Act can be found here.
Copyright Text: Herrera Consulting
2200 Sixth Avenue Suite 1100 Seattle, WA 98121
www.herrerainc.com
Color: [0, 77, 168, 255] Background Color: N/A Outline Color: N/A Vertical Alignment: bottom Horizontal Alignment: left Right to Left: false Angle: 0 XOffset: 0 YOffset: 0 Size: 10 Font Family: Bookman Old Style Font Style: normal Font Weight: normal Font Decoration: none
Description: This dataset shows areas of Mercer Island that are infeasible for infiltration based on the overlap of erosion hazard areas, landslide hazard areas, and steep slopes (> 20%). This analysis was completed in January 2018 by Herrera Consulting as part of the Infiltration Infeasibility Study project (project manager for City: Patrick Yamashita, City Engineer). This dataset is for planning purposes only and additional considerations (depth to groundwater, infiltration setbacks from environmental and site features, and site soils) should be assessed on a site-by-site basis based on the specific criteria for the BMP under consideratioin..
Copyright Text: Herrera Consulting:
JENNIFER SCHMIDT, GISP
Spatial Science Manager
direct 206 787.8233 | main 206.441.9080
2200 Sixth Avenue Suite 1100 Seattle, WA 98121
www.herrerainc.com