Urban Nuisance Flooding, Mapping Natural Infrastructure, and Collaborative Governance

Nature Force (Jamie Gauk)

• National initiative to protect communities against flooding by utilising natural infrastructure (three priority areas: BC, Ontario, Quebec) 

• BC priority is to develop a portfolio of natural infrastructure projects in the coastal Lower Mainland

• Knowledge Elicitation Workshop re: coastal flooding in Lower Mainland

• Key concerns: funding and competition challenges, regulatory and governance challenges, flooding, SLR, and land settlement, environmental concerns

• Priorities: collaborative approaches, First Nations priorities, coordination improvements

• People are generally exploring a multitude of NI projects, but facing implementation challenges (drawbacks)

• Areas of interest for implementation: public lands, erosion-prone areas, coastal Lower Mainland, future area for consideration: riverine flooding

• Areas for support: regulatory barriers- how to overcome; involvement in future projects; make efforts collaborative 

• People are interested in more knowledge elicitation workshops, in person meetings, site visits, online surveys, and expanding the scope to riverine flooding

• Interest in story maps and visualisations for NI: people generally said yes for both

• People are interested in a wide range of NI projects going forward

Story maps to showcase different natural infrastructure projects in the Fraser River Delta (Sanne Valentijn)

• Story maps are an interactive tool used to visualise difficult issues

• Allows reader to prioritise what they consume first

• Facilitates knowledge sharing and collaborative writing between projects

• An excellent opportunity to showcase different existing projects from different organisations compiled on a single platform

• Example: 360 degree photos of Mud Bay can help show the different treatments, alongside text that explains what this means

• Example: Story map of marsh recession

• Target audience? In principle, everyone/general public, but some of the language may be more familiar for people who are already familiar with natural infrastructure projects

SLR Adaptation in Mud Bay (Max van Gaalen)

• Artificially elevated islands:

• Strong waves promote marsh recession; however, artificially elevated islands can promote marsh expansion during low tide and during high tide, they can serve as a wave breaker, meaning the wave energy slows (benefits include: sediment settles promoting marsh stability and growth; protects dike)

• Sediment used to create the islands can be dredged from Fraser River and distributed also by natural processes

• Sedimentation fields:

• Help to reduce coastal squeeze and inward migration

• Ditches, brushwood dams, and cross channels allow for improved drainage, can allow for the marsh to expand seawards, reduced wave energy

• Visualisation of a pilot of sedimentation field (200 by 200 metres in Mud Bay--usually these are larger in the Netherlands)

• Serpentine/Nicomekl River mouth provides a lot of sediment, which we do need, so some form of additional sediment deposition may be needed (i.e., like the sediment pipeline that was done in Sturgeon Bay)

• From Brent: Cost analysis of pilot and ongoing maintenance? 

• From Matt: In discussion with Stephanie Chang & student, Mauricio, about analysing tipping points, when to change the intervention approach (i.e., what interventions apply to what level of SLR?)

• Within CFAS- sediment augmentation in front of the railway, but haven’t explored how many decades into the future to continue those investments based on the value of the land

• From Deborah: SLR guidance in BC has not been updated since 2011, whereas California is contemplating a bigger range of change. 

• With the marsh islands, do they need to be built over time to get the right elevation for the marsh (right conditions for marsh grass to thrive)? And the channels, are they going through the dike or are they tidal channels?

• They are tidal channels, not going through the dike

• Some low marsh is growing on islands, so ideally would want to keep that vegetation and raise the platform slowly to help them adapt. In places where they do not grow, construct the islands and marsh plants can populate from the neighbouring existing marsh near the dike.

A possible collaboration for SLR adaptation planning in Metro Vancouver (Laura Smith)

• Current provincial guidelines: prepare for 1 metre of SLR by 2100 and 50 cm by 2050

• The issue is that these guidelines do not consider climatic uncertainty nor the specifics of local ground movement (e.g., ground subsidence) 

• Need for alternative sea level rise curves that account for these elements

• SLR is a transboundary issue, yet there is currently no coordination between local governments

• A need for enhanced collaborative governance

• Different geographic and demographic contexts of the government influence their adapting planning and progress (degree of preparedness for coastal flooding)

• Similarities of how local governments address adaptive management (uncertainty)?

• Adaptive pathways approach

• Decisions based on new information

• Flood construction building requirements

• Dealing with uncertainty through a precautionary approach

• Freeboard on dykes

• Decisions based on recommendations/ trust/ what other local governments are doing

• Decisions based on what the Province says

• Enabling factors for unified storm response: wind direction, wind speed, risk colour code

• Memorandum of Understanding as chosen format (non-binding legal agreement, used in beginning of collaborative processes)

• Framework involves three main components:

• Acknowledges need for collaborative adaptation

• Three regional sea level rise curves

• An intention to collaborate in the medium-term by establishing a Standing Committee that meets annually

• Appendixes surround the following:

• Draft framework for cohesive coastal flood response

• Advocacy for provincial funding

• Critical infrastructure

Nuisance flooding in the City of Vancouver (Savannah Hasham)

• City of Vancouver experiences frequent nuisance flooding events, specifically in winter months, due to winter storms, King tides, climate change (warmer, wetter winters), and sea level rise

• Expected to become more frequent as a result of climate change

• Looking at how to utilise the “accomodate” approach and how much nuisance flooding can be tolerated through this intervention before it becomes necessary to adopt another approach (e.g., What are the tipping points?)

• Nuisance flooding (minor flood caused by high tide or other flood drivers) occurrence:

• Rainfall and snowmelt: 3-4 times a year

• Riverine and coastal: every 2-3 years

• Typically lasts less than one day

• Thresholds to be considered a nuisance flood:

• Depth of 3-10 cm

• Velocity: <3 m/s

• Impacts: minor property damage, difficult for people and emergency services to move around the city

• Limited/no building damage

• Depends on duration and timing of event

• >24 hours is bad for the economy

• Differences when it happens during weekends, holidays

• Defining the accommodate approach

• “An approach that aims to keep community assets dry rather than trying to keep floodwaters out. Buildings and infrastructure are designed in such a way that they can accommodate temporary flooding”

• Some people think it is a critical part of a flood mitigation strategy and should be used in combination with other approaches

• Tipping points are context-dependent (frequency, location, scale of impact)

• Accommodate could restrict the potential to change strategies in the future-- should be flexible and if at one point, the accommodate approach becomes insufficient to address the issues, that would become the tipping point