Puget Sound Nearshore Tidal Restriction and Wetland Mapping

Puget Sound’s large river deltas and tidal wetland habitats associated with pocket estuaries, embayments, and other shoreline features provide critical rearing and saltwater transition habitats and migration corridors for salmon and essential habitat for maintaining nearshore function ( Beamer et al. 2005 ;  Quinn 2018 ).

Numerous regional and local datasets have been produced by local tribes, counties, state, and federal agencies, however to identify restoration opportunities and track progress towards recovery (restoration) on a regional scale we need consistent and complete datasets mapping nearshore habitats for the entire Puget Sound.

In 2019, a protocol to synthesize regional data to classify tidal restrictions and wetlands by feature type and a rule-based connectivity classification was developed to map tidal restrictions and wetlands for Puget Sound’s large river deltas using aerial imagery and regional datasets (Hall et al. 2021;  PRISM Project #18-2250 ). This project (PRISM 20-1941P) aimed to adapt these protocols to synthesize and standardize regional datasets and to identify missing features using the aerial imagery and thereby developing consistent and updated regional mapping data of (1) tidal restrictions (e.g., levees, dikes, floodgates, culverts, etc.), (2) current tidal wetland extent, and (3) potential tidal wetland extent for Puget Sound nearshore habitats.

The accuracy of these datasets rely on aerial imagery, reporting in regional data, and regional reviewer feedback. We are seeking input, via local datasets, field verification, and from local experts to help improve the accuracy of the dataset. The dataset will be updated based on this feedback, however, is intended for information purposes and should not be used for regulatory authority. We recommend continued on-the-ground verification to validate features mapped using the remote sensing approach.

Previous mapping efforts focused on delineating tidal restrictions within the SHSTMP large river delta boundaries ( NOAA 2016 ;  Stefankiv et al. 2019 ) and tidal wetlands in the PMEP tidal exceedance polygons within the deltas ( PMEP 2018 ;  Brophy et al. 2019 ). This effort aimed to map tidal restrictions and tidally influenced nearshore and wetland habitat for the remainder of the Puget Sound nearshore.

We used the updated draft PMEP tidal exceedance polygons (PMEP 2022) as the baseline potential tidally influenced habitat extent (tidal wetland extent).

The  PMEP tidal exceedance extent  was developed by combining NOAA's extreme water level models with high-resolution LiDAR digital elevation models (DEMs), alongside National Wetland Inventory, local knowledge, and aerial photo interpretation, to map areas subject to tidal inundation, from ocean to head of tide, including the freshwater tidal zone ( Brophy et al. 2019 ). The PMEP extent included both current tidally influenced habitat, and historic tidal wetlands that would be inundated based on elevation but may no longer be inundated due to human alteration (such as dikes or levees).

To complement regional datasets and to capture features that could influence tidal connectivity or processes in tidal wetland habitats, we mapped restrictions within four nearshore strata, 1) seaward to the Beach Strategies NGF shoreline, 2) within the Beach Strategies NGF 0-200 ft polygon, 3) within the PMEP extent or aerial imagery-mapped tidal wetland extent, and/or 4) within a 200-ft buffer of the PMEP tidal exceedance extent.  However, to be consistent with the large river delta methods, efforts were focused on restriction features that directly abutted or intersected the PMEP, water crossings, and major roadways or railways within the study area.

We compiled 49 spatial datasets containing 267 vector layers mapping tidal restriction and wetland features from published federal, state, county, and tribal databases and direct data requests to local data stewards.

For the purposes of this project, we define tidal restrictions as man-made features (e.g., levees and dikes, roads and railways, and water crossing features like bridges, piers and docks, tide and floodgates, and culverts) that can disrupt, mute, or restrict tidal and floodplain functions, including flood storage and conveyance, nutrient processes, and hydrologic, sediment, wood, and biotic movement (adapted from Konrad 2015).

Mapping restrictions included the following steps:

1. Synthesize redundant regional database features and correct spatial alignment
2. Update removed or modified features
3. Digitize missing features
4. Classify feature types and certainty
5. Classify feature tidal connectivity and certainty

Tidal restrictions were classified by their impact on tidal connectivity using a rule-based approach based on feature type adapted from the Lower Columbia River Estuary classification strategy ( LCEP 2009 ).

For all primary features, the features proximity to potentially tidally influenced areas was indicated. We also manually determined whether the feature had armoring present, was adjacent to the shoreline but did not have armoring present, was adjacent to the shoreline but the armor status was unknown or not visible, or if the feature was not adjacent to the shoreline (NA).

Water crossing features were also classified by their crossing type as "Ocean," for docks and piers and bridges, "Stream/river" for all features crossing a visible channel, and "No visible channel," for all other features.

Features were also assigned certainty ratings, based on the data source and if they were mapped in a regional dataset, and whether they were visible in the imagery, and manual modifications to the feature alignments based on the imagery were noted.

More detailed information on dataset is available in the  metadata .

Many of these features remain flagged for local expert review and field validation to verify feature types, connectivity classifications, and alignments. The current database represents a draft, based on the regional data and manual mapping using remote sensing data, and will be updated based on reviewer feedback prior to mass distribution. However, even once published, the data are intended for information purposes and should not be used for regulatory authority.

We leveraged the methods developed in the  Large River Delta Mapping  project to use the mapped tidal restriction features to segment and classify tidally influenced polygons from base PMEP layer.

With the large river deltas, we evaluated current and potential tidal wetland habitat within the SHSTMP delta boundaries, which captured the geomorphic tidal floodplain extent. However, when evaluating the Puget Sound nearshore, we found that while many local and regional datasets exist mapping specific tidally influenced features (e.g., pocket estuaries, small river mouths), we did not find a consistent regional layer that delineated all tidally influenced areas by feature type within in the sound. The PMEP tidal exceedance extent mapped all areas subject to tidal influence, including the open ocean, therefore we needed to determine the limit of our study extent and broaden our definition of "tidal wetlands" to include tidally influenced habitats that could be impacted by nearshore tidal restrictions, such as armoring, docks and piers, and other infrastructure.

In our previous mapping of tidal wetlands in the large river deltas, we only attributed wetland features as distributary channels and fringe wetlands, over water structure wetlands, or general tidal wetlands. In mapping nearshore "tidal wetlands," we extended our scope to include a nearshore buffer, intertidal areas, embayments and pocket estuaries, and freshwater influenced habitats such as river estuaries and small river outflows. We leveraged regional and local datasets to identify and delineate these habitats to be able to assess the impact of tidal restrictions on these different tidally influenced wetlands and nearshore habitats to support salmon recovery efforts. For purposes of this project, the general term "tidal wetlands" is used to describe the dataset, however the specific tidally influenced feature types described below are used in reporting.

Mapping tidally influenced areas included the following steps:

1. Clip the draft PMEP tidal exceedance polygons (PMEP 2022) to a 1,000 foot seaward buffer of the Beach Strategies NGF shoreline.
2. Union the PMEP polygon to the NWIFC Intertidal Areas
3. Buffer tidal restrictions by 10-ft and remove buffer from wetland network
4. Attribute tidally influenced habitats by wetland type
5. Attribute tidally influenced habitats by connectivity using the tidal restrictio network

To capture both the proximate as well as the landscape impacts of tidal restrictions, we classified each wetland polygon according to its feature and landscape connectivity, using the tidal restriction network. Connectivity for each classification was rated as unrestricted, partially restricted, significantly restricted, or completely restricted, similar to the tidal restriction feature connectivity ratings, and we established a rule-based classification system to determine connectivity ratings.

Feature tidal connectivity describes the connectivity of an individual polygon based on only the tidal restriction features that immediately surround or define the polygon (or tidal wetland unit) perimeter.

Landscape tidal connectivity considers the connectivity impacts of all of the surrounding and downstream tidal restriction features and wetlands that would impact tidal flow to the wetland feature. Landscape tidal connectivity was determined by the downstream or seaward restrictions or surrounding wetland features allowing tidal connectivity regardless of the presence of less restrictive tidal restrictions or wetlands that immediately surround tidal wetland features.

Given the minimal impacts of restrictions on tidal connectivity, we classified all tidally influenced habitats by that were impacted by tidal restrictions or other human infrastructure, as "restriction-impaired."

We developed an online data portal with WDFW to share the preliminary results of mapping efforts for the Puget Sound nearshore with local area experts and regional data stewards to facilitate feedback and input on the dataset and specific features within the dataset.

The primary goal of this review is to facilitate local area expert involvement and outreach and to improve the dataset to better support regional salmon and habitat/ecosystem recovery efforts.

These data represent preliminary drafts for reviewer comment and feedback on methods and feature types. They are not intended for planning purposes or related to regulatory authority. Reviewer feedback will be incorporated into the data and subsequently published in the final dataset. 

 Access the WDFW-CFS Review Webmap Here! 

 Reviewers should evaluate CFS generated tidal restriction and tidal wetland mapping layers with the aerial imagery and insert comments on overall data structure and specific restriction and wetland feature classifications, type, and connectivity impacts. To streamline review, the original data layers used to generate the tidal restriction database are not included in this online portal but will be made available at a later date.

Additionally, features were digitized using Google Earth Imagery published in 2021/2022 and therefore may not include more recent modifications.

On the review map, there is a layer called Reviewer Comments. This is intended to be used by reviewers to add points to represent missing features, incorrect features, comments for updates to feature details or connectivity impacts, or general comments on data structure or restriction and wetland features.

There is also a layer called Areas Reviewed where reviewers can draw polygons over areas that have been reviewed and points added to correct or identify features or covering features that were reviewed and correctly mapped.

We are also able to update the data with local datasets that may not be included in the existing data inventory. If you know of a dataset that is not included in the inventory and would like to share it, please reach out to us directly.

Lastly, we are hosting meetings with local area experts and stakeholders to directly review the data and to correct the dataset in real time based on input. Please reach out over email to let us know if you would rather add input via meeting.

Shelby Burgess (shelby.burgess@fishsciences.net)

Jason Hall (jason.hall@fishsciences.net)

The datasets produced as part of this effort are intended to be used for restoration planning (such as identifying or prioritization of restoration opportunities) and regional habitat status and trends monitoring and evaluation of progress towards recovery (e.g., Puget Sound Indicators).

For example, the  Large River Delta Mapping  was used to support the development of the  Estuary Area in Functional Condition Vital Sign Indicator . The dataset represents current conditions (circa 2019) of tidal restriction and wetland habitat in the large river deltas within the SHSTMP delta boundaries. The current effort to expand mapping of tidal restrictions and tidally influenced habitat for the rest of the Puget Sound nearshore will support the development of the  Accessible Pocket Estuaries and Embayments Vital Sign Indicator .

After the current datasets are finalized, they will be integrated with the large river delta tidal restriction and wetland database and will be shared publicly on an  ArcGIS web map , with tools to support querying and summarizing by user-specified inputs. This web map can also support continued regional expert review and comment, but a protocol is needed for incorporating these comments into the data and updating the dataset periodically to reflect changes from restoration or development.