South Fork Skagit Restoration Monitoring to Develop and Test Restoration Design Tools

Nearshore Database Project Number: 07-1107

Proponent Contact Info: Steve Hinton Skagit River System Cooperative Director of Restoration [email protected] (360) 466-7243

Site Access Contact Info: W. Gregory Hood Skagit River System Cooperative Senior Restoration Ecologist [email protected] (360) 466-7282

Site Location: South Fork Skagit River Delta, including Deepwater Slough restoration site Milltown Island restoration site Wiley Slough restoration site Fisher Slough restoration site Reference tidal marshes All sites are located on the Skagit River, downstream from Conway, WA. Latitude 48.315˚ Longitude -122.365˚

Start Date: January 2008 End Date: December 2009

Key Personnel: W. Gregory Hood, Phd, Senior Restoration Ecologist Project manager and Scientist Will plan and implement the monitoring program, direct fieldwork, analyze data, and report and disseminate results. Problem Statement Restoration monitoring is sometimes perceived as not having delivered value to management agencies. Consequently, agencies are reluctant to fund monitoring, preferring instead to fund only restoration. The criticism of monitoring is valid and the causes of its failure are multiple, among them: [a] funding for monitoring is often inconsistent or unreliable (which leads to inconsistent and unreliable monitoring, and a catch-22 situation); [b] monitoring is often mere comparison of reference and restoration sites rather than hypothesis testing, [c] monitoring often requires long-term observation (patience) incompatible with short-term performance requirements of many agencies; and [d] monitoring often does not deliver useful information on which agencies can act. In support of Chinook salmon recovery, we propose to deliver value through a monitoring project that develops and tests restoration design and planning tools that could be used throughout Puget Sound. The tools we will develop and test are [1] a predictive model of tidal marsh vegetation that uses marsh elevation (tidal flooding frequency and duration), soil salinity, and sediment grain size to generate probabilistic predictions of vegetation occurrence; and [2] a predictive model of dendritic tidal channel geometry. We will also acquire data necessary to develop [3] a conceptual model of distributary channel dynamics. In addition to quantitatively predicting the tidal marsh vegetation that would develop following dike breaching or removal, the vegetation model would also allow modelling of climate change scenarios (sea-level rise and changes in salinity and sediment dynamics) to predict restoration sustainability (Hood 2005). The predictive dendritic channel geometry model can be used to predict the amount of juvenile Chinook salmon habitat and abundance resulting from marsh restoration. The distributary dynamics model will be applicable to distributary restoration, e.g., across Fir Island.

Existing Information/Previous Work [1] Vegetation model. The first step in developing a predictive model for tidal marsh vegetation has already been accomplished. Survey-grade GPS (2-cm horizontal and vertical accuracy) sampling of the South Fork Skagit tidal marshes has generated a data set of over 600 data points that pair observed elevation and vegetation (Fig. 1).

Figure 1. Box-plot of the elevation distributions of common marsh vegetation in the South Fork Skagit tidal marshes (blue), compared to vegetation in the Deepwater Slough restoration site (red) prior to dike removal (the site had poorly drained, fallow fields prior to dike removal). Sample sizes are in parentheses. Shaded and unshaded portions of the boxes represent the 2nd and 3rd quartiles around the median, vertical lines represent two standard deviations from the mean, and stars are outliers.

1 These data can be reorganized to generate probability functions for species occurrence at a given elevation range (Fig. 2), which can then be used to recode lidar data to generate probabilistic vegetation predictions (Fig. 3). This preliminary model has been tested by

Figure 2 (left) Vegetation species occurrence probabilities relative to marsh elevation.

Figure 3 (right) Probabilities of encountering Carex lyngbyei (sedge) [top], Typha angustifolia (cattail) [middle], and Myrica gale (sweetgale) [bottom] on the Fisher Slough project site following proposed tidal restoration. Warm colors are high probabilities, cool colors are low probabilities. White areas are either off-site or have probability of zero.

monitoring vegetation changes in the Deepwater Slough restoration site (restored in summer of 2000) and performing an adaptive management experiment (2003-2007). The results to date are encouraging and suggest this modelling approach has a strong likelihood of successfully predicting marsh vegetation following tidal regime restoration. [2] Dendritic tidal channel model. Planform dendritic tidal channel geometry has been modelled for the Skagit marshes by scaling tidal channel metrics with marsh area. Details are described in Hood (2007), and the results indicate significant utility in planning optimal marsh restoration designs. For example, to maximize tidal channel surface area and length it is better to restore one large continuous parcel than several

2 smaller separate parcels. The results were also used to infer anthropogenic impacts (river distributary obstruction) to a significant portion of the Skagit marshes. [3] Distributary channel conceptual model. Analysis of the recent development of a river distributary in the North Fork Skagit tidal marshes indicates that relative distributary gradient is a reasonable predictor of distributary size (Hood 2004; Hood, unpublished data). Similar analysis of simple parts of the South Fork distributary system shows promise as well, but the current approach does not yet account for complex anastomosing patterns that are also present in the South Fork delta.

Data Gaps [1] Vegetation model. The current vegetation model describes only oligohaline tidal marshes, and thus is constrained to a narrow range of conditions. To make the model more general requires inclusion of additional environmental influences on tidal marsh vegetation distribution, particularly soil salinity and grain size. This will allow prediction for a larger variety of marshes and for likely climate change influences. [2] Dendritic tidal channel model. The current model is based only on planform geometry quantifiable from high-resolution orthophotos. A more complete and generalizable model will require vertical information as well, i.e., surveys of channel cross-sections to acquire depth and cross-sectional area. Vertical information will also allow better linkage of channel geometry to fish use by estimating channel capacity (accessibility to fish during the tidal cycle). [3] Distributary conceptual model. This model also lacks vertical information, i.e., channel cross-section data.

Proposed Work Data Acquisition for Model Parameterization [1] Vegetation model. We will collect paired elevation-vegetation data in Skagit Delta tidal marshes with a variety of soil salinities, similar to that already collected in the oligohaline portion of the South Fork Skagit delta [0-8 ppt]. Collection sites will include [a] Skagit bay-fringe marshes (10-18 ppt) between the North and South Fork tidal marshes (where historical distributaries are now blocked by dikes); [b] marshes in the southern-most portion of the South Fork delta [8-12 ppt]; and marshes fringing [c] Port Susan Bay [10-18 ppt]; [d] the Swinomish Channel (20-25 ppt); [e] Padilla Bay (25-30 ppt); and [f] Samish Bay [20-25 ppt]. Elevations will be measured relative to survey benchmarks and known tidal datums with either survey-grade GPS or laser levels. We anticipate acquiring 1500 to 2000 data points. We will measure grain size in marshes associated with various geomorphic characteristics (proximity to river distributaries, areas of dynamic historical change, and wave fetch). GIS analysis of current and historical air photos will be used to determine sampling locations. Vegetation and elevation will be simultaneously sampled with sediment grain size. Preliminary field observations indicate that sediment types (sandy vs silty vs clay/mud) can occur in distinct patches and zones in the Skagit system with distinct effects on tidal marsh vegetation. [2] Dendritic tidal channel model. Channel cross-sections will be surveyed with either survey-grade GPS or laser levels relative to known bench marks and tidal datums. Cross-sections will be surveyed at channel outlets, at ¼ of the channel length inland from

3 the outlet, and at the channel midpoint. Cross-sections will include elevation of each bank for a distance of at least 20 m to characterize channel berms and marsh elevation. We anticipate surveying at least 100 tidal channels (300 cross-sections) spanning a large range of sizes and broadly distributed in the Skagit marshes. All data will be spatially identifiable and entered into a GIS. [3] Distributary conceptual model. Channel cross-sections will be surveyed for all South Fork Skagit River distributaries above and below distributary junctions and divergences. To support data collection and model testing for all three models we propose acquisition of new high-resolution (15-cm pixel) infra-red orthophotos of the South Fork Skagit marshes in either 2008 or 2009, depending on when the Wiley Slough and Fisher Slough restoration projects are implemented (implementation for Wiley Slough is expected in the summer of 2007).

Analysis and Model Construction [1] Vegetation model. The new vegetation model will be constructed similarly to the existing 1-parameter (elevation-only) model. Model form will depend on the nature of the data collected (range and covariance structure). It could consist of an integrated 3- parameter model (elevation, soil salinity, and grain size), the preferred approach, or separate models stratified or classified by soil salinity and grain size. [2] Dendritic tidal channel model. Channel cross-sections will be analyzed and incorporated into an allometric model of tidal channel geometry as described for planform metrics in Hood (2007). Channel depth will be related to inundation frequency, duration, and depth using available tide gage data for the South Fork marshes. Size- dependent maximum residence time of fish (juvenile salmon vs potential aquatic predators) will be inferred from the tidal regime and channel depth. [3] Distributary conceptual model. Channel cross-sections will be inputs to standard channel hydraulic models to improve on our existing (unpublished) conceptual model of distributary dynamics. The cross-section data will also be used to improve the bathymetry of an existing 3-dimension hydrodynamic model of the Skagit Delta and Bay developed by Drs. Tarang Khangaonkar and Zhaoqing Yang of the Battelle Pacific Northwest National Laboratory. Distributary bathymetry is essentially unknown in the Skagit Delta, and this has significant consequences on model accuracy and system dynamics.

Model testing (Restoration Monitoring) The Deepwater Slough, Wiley Slough, Milltown Island, and Fisher Slough restoration sites will be monitored through field surveys of vegetation and channel cross- sections, including off-site channels (downstream channels or distributaries adjacent to removed dikes) which are likely to respond to site restoration (Appendix A). New infra- red orthophotos will also be acquired to monitor channel planform and marsh vegetation on a broader scale, including the dynamic reference marshes. Monitoring results will be compared to predictions developed from all three models. Preliminary monitoring and testing of existing models illustrate the proposed approach. Predictions of the 1-parameter vegetation model for Deepwater Slough match observed monitoring results (Fig. 4) and the results of an adaptive management

4 experiment (Fig. 5). Likewise, observed tidal channel development indicates restoration trajectories moving towards predicted equilibrium points (Fig. 6). Predictions made be the river distributary conceptual model will be compared against the observed trajectory of changes in the Deepwater Slough distributary (directly affected by the Deepwater Slough restoration project) and the Freshwater Slough Distributary (indirectly affected by restoration of the Deepwater Slough distributary).

Figure 4. [left] The Deepwater Slough restoration site, west lobe, during dike removal (gray linear features). The poorly drained site was already dominated by non-native narrow-leaf cattail (Typha angustifolia) and reed canarygrass (Phalaris arundinacea), but do to dike-modified hydrology they grew at elevations at which native sedge (Carex lyngbyei) and spikerush (Eleocharis palustris) are found in the reference tidal marshes and at which cattail and canarygrass are uncommon (cf. Fig. 1). In the absence of competition from pre- established non-natives, the bare-earth footprint of the removed dike became colonized by sedge and spike rush [right] as predicted by the 1-parameter model.

Figure 5. To further test the 1-parameter model, we mowed 3.3 acres of non-native cattail [pink and gray portions of inset figure, cf. yellow square of Fig. 4] to remove pre-emptive competition and thereby facilitate colonization by native vegetation. After two seasons of mowing most cattails were dead stumps [left] and most colonizing plants were native water plantain (Alisma triviale). The next year most of the site was colonized by native sedge and spikerush as predicted by the 1-parameter model.

5 Figure 6. Comparison of Deepwater Slough restoration trajectories for the west, east, and central lobes of the project (red = 2000, blue = 2004) with the allometric equilibrium geometry of reference marsh islands (gray circles) generated by the planform dendritic tidal channel model. Channel count is the number of tidal channels draining a site. Marsh magnitude is the count of 1st – order channels (a measure of network complexity). The bottom graph illustrates scaling in channel form and indicates that the restoration site channels are “fatter” or “stubbier” than the reference marsh dendritic tidal channels. The top two graphs suggest the tidal channels of the restoration site are becoming more similar to those of the reference marshes with regard to the number of channels draining a site and the complexity of the drainage network, while the bottom graph suggests little movement toward the reference condition with regard to channel “stubbiness”.

Anticipated Products We anticipate developing quantitative predictive models of tidal marsh vegetation and tidal channel geometry that will be useful for restoration planning and design for projects throughout Puget Sound. The addition of new parameters (soil salinity and grain size for the vegetation model, and channel depth and cross-sectional area for the channel geometry model), should make these model generalizable beyond the Skagit Delta. We also anticipate developing a conceptual model of distributary dynamics that will allow at least preliminary development of a general (not site-specific) predictive model of distributary geometry and trajectories, useful for planning purposes. More detailed engineering designs would still require site-specific hydrodynamic models. All models and monitoring results will be thoroughly described in technical reports to funding agencies and in peer-reviewed scientific literature. They would also be presented in local, regional, and national conferences.

Citations Hood WG. 2007. Scaling tidal channel geometry with marsh island area: a tool for habitat restoration, linked to channel formation process. Water Resources Research 43, W03409, doi:10.1029/2006WR005083. Hood WG. 2005. Sea Level Rise in the Skagit Delta. Skagit River Tidings, 2005. Skagit Watershed Council, Mount Vernon, Washington. Hood WG. 2004. Distributary Channel Development Processes in the Skagit Delta. Skagit River Tidings, 2004. Skagit Watershed Council, Mount Vernon, Washington.

6 Appendix A

Figure A. Monitoring site locations. Dw = Deepwater Slough restoration, west lobe, Dc = Deepwater Slough restoration, central lobe, De = Deepwater Slough restoration, east lobe [all Deepwater lobes were restored in 2000]; W = Wiley Slough restoration [implementation anticipated for summer 2007]; M = Milltown Island [implemented in two stages, summer 2006 and summer 2007]; F = Fisher Slough [implementation anticipated for summer 2008 or 2009]. Additional restoration monitoring will occur off- site in areas likely to be affected by restoration, downstream tidal channels and nearby distributaries. Reference marshes will include all tidal marshes in the greater Skagit Delta.

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