Response to Dike Alteration Scenarios Noel Bacheller, OPRD Botanist - PowerPoint PPT Presentation

Modeled Beltz Marsh Vegetation Response to Dike Alteration Scenarios Noel Bacheller, OPRD Botanist November 2019

Exis xistin ing Vegetation patterns • Existing vegetation types as of 2015 are well documented • Broad habitat types in Beltz Marsh and Sand Lake follow predictable patterns based on elevation and the amount of tidal inundation areas receive

Vegetation patterns and modelin ing pot otentia ial fu futu ture sce cenarios • Vegetation was first modelled in 2015 for preliminary scenarios, which have changed significantly in the past 2 years • 2015 modeling was based on water surface elevation modeling done by Waterways, Inc for the scenarios: existing tide gate, tide gate flap removal, 18ft active channel width breach • Past vegetation modeling methods and code were easily adapted to new scenarios under consideration today • This 2019 vegetation modeling is based on a 7.5 month tidal simulation period produced by ESA during the surface and groundwater modeling project of 2017-2019 for the scenarios: existing tide gate, modern tide gates, 40’ breach, and setback dike.

Vegetation patterns ou outs tside th the dik ike • A common way of predicting vegetation by elevation in estuaries is to refer to vegetation Classification Tree trained on known vegetation Current pattern outside dike type boundaries relative to Mean Higher High Ft. Relative to Water (MHHW) Ft NAVD88 MHHW 12 3.4 11.8 3.2 11.6 Forested Wetland 3 11.4 2.8 11.2 2.6 11 2.4 10.8 Scrub-Shrub Wetland 2.2 10.6 2 10.4 1.8 10.2 1.6 10 1.4 9.8 1.2 9.6 Freshwater Marsh 1 9.4 0.8 9.2 0.6 9 0.4 8.8 High Saltmarsh 0.2 8.6 0 8.4 -0.2 8.2 -0.4 8 -0.6 7.8 -0.8 7.6 Low Saltmarsh -1 7.4 -1.2 7.2 -1.4 7 -1.6 6.8 -1.8 6.6 -2 6.4 -2.2 6.2 -2.4 6 Water/Mud -2.6 5.8 -2.8 5.6 -3 5.4 -3.2

Application of of vegetation patterns ou outsid ide th the dik ike to o pot otentia ial fu future sce scenarios: Mod odern tid tide gates • Using the known pattern of vegetation relative Applying outside pattern to Current pattern outside dike modeled modern tide gate to MHHW, we can shift the “bathtub rings” of Ft. Relative to Ft. Relative to vegetation downward according to the predicted Ft NAVD88 MHHW_SL Ft NAVD88 MHHW_MG 12.6 (Upland) 4 12.6 5.4 new MHHW 12.4 3.8 12.4 5.2 12.2 3.6 12.2 5 12 3.4 12 4.8 • This is overly simplistic, but gives an easy way to 11.8 3.2 11.8 4.6 11.6 Forested Wetland 3 11.6 4.4 approximately visualize it . 11.4 2.8 11.4 (Upland?) 4.2 11.2 2.6 11.2 4 11 2.4 11 3.8 10.8 Scrub-Shrub Wetland 2.2 10.8 3.6 • MHHW for Sand Lake=8.6 10.6 2 10.6 3.4 10.4 1.8 10.4 3.2 • MHHW for inside dike with modern tide gates 10.2 1.6 10.2 Forested Wetland 3 10 1.4 10 2.8 =7.2 9.8 1.2 9.8 2.6 9.6 Freshwater Marsh 1 9.6 2.4 • MHHW for the existing condition = 7.3 9.4 0.8 9.4 Scrub-Shrub Wetland 2.2 9.2 0.6 9.2 2 9 0.4 9 1.8 8.8 High Saltmarsh 0.2 8.8 1.6 8.6 0 8.6 1.4 8.4 -0.2 8.4 1.2 8.2 -0.4 8.2 Freshwater Marsh 1 8 -0.6 8 0.8 7.8 -0.8 7.8 0.6 7.6 Low Saltmarsh -1 7.6 0.4 7.4 -1.2 7.4 High Saltmarsh 0.2 7.2 -1.4 7.2 0 7 -1.6 7 -0.2 6.8 -1.8 6.8 -0.4 6.6 -2 6.6 -0.6 6.4 -2.2 6.4 -0.8 6.2 -2.4 6.2 Low Saltmarsh -1 6 Water/Mud -2.6 6 -1.2 5.8 -2.8 5.8 -1.4 5.6 -3 5.6 -1.6 5.4 -3.2 5.4 -1.8 5.2 -3.4 5.2 -2 5 -3.6 5 -2.2 4.8 -3.8 4.8 -2.4 4.6 -4 4.6 Water/Mud -2.6 4.4 -4.2 4.4 -2.8 4.2 -4.4 4.2 -3 4 -4.6 4 -3.2

Appli lication of of veg egetation patterns ou outs tsid ide e th the e dik ike e to o pot otentia ial fu futu ture e scen cenarios: Br Breach Current pattern outside dike Breach prediction Ft. Relative to Ft. Relative to Ft NAVD88 MHHW_SL Ft NAVD88 MHHW_SL 12.6 (Upland) 4 12.6 (Upland) 4 12.4 3.8 12.4 3.8 12.2 3.6 12.2 3.6 • Because the breach scenario results in the same 12 3.4 12 3.4 11.8 3.2 11.8 3.2 water levels inside the dike as outside the dike at 11.6 Forested Wetland 3 11.6 Forested Wetland 3 11.4 2.8 11.4 2.8 all times, the vegetation patterns seen outside 11.2 2.6 11.2 2.6 11 2.4 11 2.4 the dike should be the same as those that would 10.8 Scrub-Shrub Wetland 2.2 10.8 Scrub-Shrub Wetland 2.2 occur inside the dike 10.6 2 10.6 2 10.4 1.8 10.4 1.8 • This is overly simplistic, but gives an easy way to 10.2 1.6 10.2 1.6 10 1.4 10 1.4 approximately visualize it . 9.8 1.2 9.8 1.2 9.6 Freshwater Marsh 1 9.6 Freshwater Marsh 1 • There are also considerations of vegetation 9.4 0.8 9.4 0.8 9.2 0.6 9.2 0.6 resiliency that need to be factored in 9 0.4 9 0.4 8.8 High Saltmarsh 0.2 8.8 High Saltmarsh 0.2 8.6 0 8.6 0 8.4 -0.2 8.4 -0.2 8.2 -0.4 8.2 -0.4 8 -0.6 8 -0.6 7.8 -0.8 7.8 -0.8 7.6 Low Saltmarsh -1 7.6 Low Saltmarsh -1 7.4 -1.2 7.4 -1.2 7.2 -1.4 7.2 -1.4 7 -1.6 7 -1.6 6.8 -1.8 6.8 -1.8 6.6 -2 6.6 -2 6.4 -2.2 6.4 -2.2 6.2 -2.4 6.2 -2.4 6 Water/Mud -2.6 6 Water/Mud -2.6 5.8 -2.8 5.8 -2.8 5.6 -3 5.6 -3 5.4 -3.2 5.4 -3.2 5.2 -3.4 5.2 -3.4 5 -3.6 5 -3.6 4.8 -3.8 4.8 -3.8 4.6 -4 4.6 -4 4.4 -4.2 4.4 -4.2 4.2 -4.4 4.2 -4.4 4 -4.6 4 -4.6

Appli lication of of veg egetation patterns ou outs tsid ide e th the e dik ike e to o pot otentia ial fu futu ture e scen cenarios: im improved mod odeli ling meth thods • Shifting vegetation elevation “bathtub rings” Applying outside pattern to Current pattern outside dike modeled modern tide gate downward might work OK for the upper Ft. Relative to Ft. Relative to elevations, but probably not for lower Ft NAVD88 MHHW_SL Ft NAVD88 MHHW_MG 12.6 (Upland) 4 12.6 5.4 elevations. 12.4 3.8 12.4 5.2 12.2 3.6 12.2 5 • This is because the lower limit of water level is 12 3.4 12 4.8 11.8 3.2 11.8 4.6 controlled and cannot go below 5.5ft NAVD88. 11.6 Forested Wetland 3 11.6 4.4 • This may imply reduced ranges for the lower- 11.4 2.8 11.4 (Upland?) 4.2 11.2 2.6 11.2 4 lying vegetation zones than would be predicted 11 2.4 11 3.8 10.8 Scrub-Shrub Wetland 2.2 10.8 3.6 with a simple shift. 10.6 2 10.6 3.4 10.4 1.8 10.4 3.2 • There are gray areas between the vegetation 10.2 1.6 10.2 Forested Wetland 3 10 1.4 10 2.8 zones where vegetation types can overlap in 9.8 1.2 9.8 2.6 9.6 Freshwater Marsh 1 9.6 2.4 inundation tolerance range… simplistic 9.4 0.8 9.4 Scrub-Shrub Wetland 2.2 9.2 0.6 9.2 2 maximum likelihood models give sort of a 9 0.4 9 1.8 8.8 High Saltmarsh 0.2 8.8 1.6 winner takes all output 8.6 0 8.6 1.4 8.4 -0.2 8.4 1.2 • Reality will likely mean that there will be some 8.2 -0.4 8.2 Freshwater Marsh 1 8 -0.6 8 0.8 uncertainty in what vegetation will win out in 7.8 -0.8 7.8 0.6 overlapping niches 7.6 Low Saltmarsh -1 7.6 0.4 7.4 -1.2 7.4 High Saltmarsh 0.2 • There will be an incumbent advantage for 7.2 -1.4 7.2 0 7 -1.6 7 -0.2 vegetation types that are already in place 6.8 -1.8 6.8 -0.4 6.6 -2 6.6 -0.6 • Allowances needed for: 6.4 -2.2 6.4 -0.8 6.2 -2.4 6.2 Low Saltmarsh -1 • resiliency of existing vegetation 6 Water/Mud -2.6 6 -1.2 5.8 -2.8 5.8 -1.4 • chance 5.6 -3 5.6 -1.6 5.4 -3.2 5.4 -1.8 5.2 -3.4 5.2 -2 5 -3.6 5 -2.2 4.8 -3.8 4.8 -2.4 4.6 -4 4.6 Water/Mud -2.6 4.4 -4.2 4.4 -2.8 4.2 -4.4 4.2 -3 4 -4.6 4 -3.2

Appli lication of of veg egetation patterns ou outs tsid ide e th the e dik ike e to o pot otentia ial fu futu ture e scen cenarios: im improved mod odeli ling meth thods Water Surface Elevation Digital Elevation Hydrograph Model 1. Use topography and surface water model to create predictor variable maps of • Average daily maximum depth of water by month • Monthly maximum depth of water • Average daily duration of inundation by month • Monthly maximum duration of inundation February average daily maximum duration of inundation

Appli lication of of veg egetation patterns ou outs tsid ide e th the e dik ike e to o pot otentia ial fu futu ture e scen cenarios: im improved mod odeli ling meth thods 1. Use topography and surface water model to create predictor variable maps of • Average daily maximum depth of water by month • Monthly maximum depth of water • Average daily duration of inundation by month • Monthly maximum duration of inundation 2. Extract values from these predictor maps to known vegetation types outside the dike

Appli lication of of veg egetation patterns ou outs tsid ide e th the e dik ike e to o pot otentia ial fu futu ture e scen cenarios: im improved mod odeli ling meth thods 1. Use topography and surface water model to create predictor variable maps of • Average daily maximum depth of water by month • Monthly maximum depth of water • Average daily duration of inundation by month • Monthly maximum duration of inundation 2. Extract values from these predictor maps to known vegetation types outside the dike 3. Create a database of vegetation type vs hydrological values