Projects that impact wetlands require a synthesis of science, planning, and engineering design from the start when assessing ecosystem impacts. Cross-functional teams that identify and integrate site-specific data into analyses will ask better questions, avoid oversights, and reach more balanced solutions. At Herrera wetland scientists and engineers coordinate throughout the design process to optimize designs and community results. Creating a team skilled in all facets of science, planning, and design is crucial for developing comprehensive wetland solutions.
Neil Schaner, Senior Engineer at Herrera, outlines some of the questions that wetland scientists should ask design engineers, especially when working on projects in Western Washington:
Ask what stormwater requirements need to be met.
Most projects trigger a variety of Ecology’s stormwater Minimum Requirements (MRs), including Flow Control, On-Site Stormwater Management, and Runoff Treatment. If a wetland is associated with the project, Wetlands Protection will also be triggered. The level of protection required, including if a monitoring campaign is required, is primarily based on the wetland category. Wetlands Protection takes precedence over the other requirements. Jurisdictions may have requirements different than Ecology’s but most are similar.
Ask about the data used in the analysis.
Design engineers often use Ecology-approved continuous simulation hydrology models (e.g., WWHM or MGSFlood) to evaluate Ecology’s stormwater MRs, including the Wetland Protection MR. Scientists should ask what data was used to build the hydrology model and if there are any broad assumptions being made.
Ask what precipitation and evapotranspiration data is being used.
The Ecology approved models use pre-loaded precipitation and evaporation records that may not be accurate for the project site and that do not account for forecast climate change. A local precipitation record will result in more accurate simulations of runoff rates and volumes flowing to wetlands. Analyzing the project with a precipitation record perturbed for forecast climate change allows the design to mitigate for future wetland impacts to the greatest extent feasible.
Ask about the parameters being used to define land use, how precipitation is converted to runoff, and how it is routed to wetlands.
When modeling land use and runoff, the Ecology approved models’ default parameters are very generally calibrated for Western Washington. For example, forest parameters are based on a second growth, Douglas fir dominant forest; land surface slopes are 5, 10, or 15 percent; and overland flow path length is 400 feet for everything. Each of these parameters impact the timing and volume of runoff assumed to enter wetlands. Rarely will any one site present conditions that match these default values. If the defaults aren’t appropriate, request they be adjusted for site specific conditions.
Ask what supplemental data exists or can be created to holistically evaluate the potential impacts to the site.
This is obvious, but engineers are not experts in wetland science. However, we may be able to provide supplemental data or produce specific hydrologic simulation results that when reviewed by a wetland scientist can better determine project impacts.
Tell me about wetland species and how they can be protected.
At Bellingham’s Cordata Park, scientists identified Pacific chorus frogs and long-toed salamanders in one of the site’s wetlands. Based on known preferences and breeding habits, the project scientists identified ideal maximum wetland water level fluctuations and the most important months to maintain the existing wetland conditions. Using the project hydrology model and supplemental spreadsheets, we analyzed the wetland hydroperiod with an eye toward species protection. The design was adjusted to reduce impacts to the frogs and salamanders to the greatest extent possible while achieving other project goals.
Takeaways:
Regular collaboration between wetland scientists and engineers on site-specific analysis and results interpretation increases confidence that a project design is fully assessed and addresses short- and long-term impacts. The design of Bellingham’s Cordata Park was a success partly due to simulating detailed land use scenarios, enabling engineers and wetland scientists to iterate toward a solution together. While more complex tools exist, the Ecology-approved continuous simulation models can produce accurate results for complex projects when correctly configured.
At Herrera, our team views cross-discipline collaboration as generating transparency, ethical accountability, and public trust. We collectively take ownership in this responsibility out of respect for the communities and ecologies affected through our work.
