Assessing Geological Hazards

Assessing Geological Hazards 4 of 30

. . . to develop a methodology to incorporate geology into the land use planning process

Geohazards are events caused by geological features and processes that present severe threats to humans, property and the natural and built environment.

Picture from NS DNR Geological Services Division

Geohazards?



• coastal flooding and riverine flooding• coastal erosion• land sinking – sinkholes• contamination of water from heavy metals

in soil or acid rock drainage• landslides / slope failure

Geo-events that pose threats




How do we realistically handle these geohazards in our MCCAPs?



2 climate drivers

1.Sea level rise

2.Changes in precipitation

BIO’s relative sea level rise estimates

0.4-0.9m on 50-year time scale

0.9-1.6 on 100-year time scale

Example from

County of Colchester / Truro

MSC’sSTORM SURGE MODEL

Tell us the impacts you are seeing and at what water levels!

Model based on OUTPUT WINDS


Map display; every hour for 48 hrs out from when model run

Time series graph; point forecast for specific location. Show stage 1, 2 or 3 flooding based on past events.


Does NOT include wave run up

Add 10% to surge levelsif wind facing shoreline . . .

. . . then add tide level


65cm surge predicted at nearly high tide = 2.9m

75-80 cm surge experienced = so 3m + at least another 10cm for wave run up

(more if wind from S/SE)

Observed sea level rise exceeded what the Intergovernmental Panel on Climate Change (IPCC) predicted by 50% for the period 1990–2006.

80% of the rise in sea level between during 2003–2008 is believed to be from ice melt

0.42 ± 0.15 0.57m upper uncertainty for relative SLR

So use 0.57m

Water Surplus

Water Deficit

Intensity Short Period Rainfall

In a 20 year return period rainfall:

• 5% more rain by 2020s

• 9% more by 2050s

• 16% more by 2080s

Anne [email protected] 431 7168

www.elementalsustainability.ca

Geohazards?

1. What’s the short-list of geohazards potentially relevant to my MCCAP?

2. How are they relevant, and are they priorities?

THANK YOU!• Garth DeMont, Geoscientist with NS Department of Natural Resources• Gavin Kennedy, Hydrogeologist with NS Department of Natural Resources• John Drage, Hydrogeologist with NS Department of Natural Resources



• coastal flooding & riverine flooding• coastal erosion• land sinking – sinkholes• contamination of water from heavy

metals in soil or acid rock drainage• landslides / slope failure






Geohazard—Coastal erosion


The need to establish setbacks should be informed by geology – both bedrock and surficial

Coastal erosion risk will increase with sea level rise.




Geohazard—Karst


Occurs inlimestone & gypsum

• sinkholes• water contamination

Under the Nova Scotia Treatment Standard for Municipal Surface Source Water Treatment Facilities, once designated, karst areas are subject to water treatment standards.



Geohazard—Heavy Metals

Toenails, Tap Water and You: The Arsenic ConnectionNS DNR Report of Activities: 2009

Assessing Geological Hazards 4 of 30Geohazard—Heavy Metals

Toenails, Tap Water and You: The Arsenic ConnectionNS DNR Report of Activities: 2009

In unstable climatic conditions where rocks and soilsare saturated one week and dry the next there is ahigher risk of transport into groundwater systems.

Will that be our climate?

Assessing Geological Hazards 4 of 30Geohazard—Acid rock drainage

Pyrite and pyrrhotite oxidize when exposed to air, resulting in production of sulphuric acid and iron oxides.

Sulphuric acid is soluble.

Picture from NASA Earth Science Division

Assessing Geological Hazards 4 of 30Geohazard—Acid rock drainage

The amount of water that will fall in a ‘20 year return period’ rainfall (i.e., an event that has a 5% chance of happening any given year) will be:

5% more rain fall by the 2020s9% more rain will fall by 2050s

16% more rain fall by the 2080s.

Picture from NASA Earth Science Division



Geohazard—Slope stability

• Slope angle?• What’s beneath our feet? On surface and underlying?• How saturated is it?• How warm is it?

different kind of assessment than coastal erosion Slope Stability Guidelines for Development Applications

Decision Flow Diagram

Assessing Geological Hazards

•Understand how climate change can trigger certain hazards

•Are any of these hazards present in my jurisdiction?

•Where?

•Do they impose an intolerable risk?

•How urgent is the need to respond?



Assessing changes in precipitation






Update the Draft Stormwater Management Plan

Recommend BMPs so that future development won’t increase peak runoff flows


Update the Draft Stormwater Management Plan

Recommend BMPs so that future development won’t increase peak runoff flows

Assess the effects of climate change on rainfall intensity and the effects of these changes on the storm water mgt plan

SWMM5

Stormnet


New climate-wise design rainfalls

Stormnet



What’s the rainfall pattern during the day: sub-day durations? (used for IDF curves)



Conclusions:

•Predicted magnitude of the increase in precip volume expected in 1 day is 29%

•Predicted increases for 24 hr rain are higher than increases in annual rainfall

•Predicted increases for shorter durations are greater than increases for longer

durations


StormnetDesign Storms



•redefine peak flows to be associated with

potential future rainfall events

•estimate the equivalent pipe diameter of culverts required to convey the peak flows, and

•estimate the costs for culvert replacements to accommodate peak flows


Minor Drainage System


Designed for rainfall events with return periods of1 in 5 to 1 in 10 , based on HISTORICAL RECORD.


Designed for rainfall events with return periods of1 in 5 to 1 in 10 , based on HISTORICAL RECORD.

Rainfall events in exceeding this cause surcharge:Up-the-pipe-flooding


Major Drainage System

Natural water channels tend to have capacity for a 1 in 2 year rainfall event, based on historical records



The level of service expected by the public and other stakeholders is rising


Recommendation:

All structures with capacity less than the estimatedmaximum peak runoff flows predicted by the

(stormnet) modeling should be upgraded.



4 Recommendations:

1. Examine each watershed in the Town, starting with the watershed where the potential risk of flood damage is greatest, and figure out:

• if and where there are opportunities to increase the capacity for water storage/detention and

• if existing culverts and structures could withstand a 1 in 100 year return period rainfall as defined by simulated rainfall events modeled in the study.



4 Recommendations:

2. Identify flood limits generated by the design rainfall event with 1 in 100 year return period on Town Land Use Mapping



4 Recommendations:

3. DEFINE acceptable level of (stormwater mgt) service in consultation with stakeholders



4 Recommendations:

4. Develop a prioritized list of modifications to existing structures (e.g. culverts), based on what they now knew about the condition and capacity of existing culverts, as well as stakeholder views on acceptable levels of flood risk


. . . to develop a methodology to incorporate geology into the land use planning process Plan to adopt the

updated Plan at the Jan. 2013 Council mtg


. . . to develop a methodology to incorporate geology into the land use planning process A stormwater mgt

plan will have to be submitted as part of all development applications



Take away messages:

•Work at the watershed level

•Engage climatologists to model and downscale design rainfalls

•Ask about the modeling software

•Visually present flood hazard and risk to stakeholders

When does an impact become a priority?

Adaptive capacity is the ‘action’ component, the dynamic ability to respond and adapt in the face of change.

Adaptive capacity refers to the combination of assets and resources that form the base from which adaptation actions and investments can be made.

. . . adaptive capacity considers processes and response. Aspects such as flexibility, redundancy, experience, and networks of support can all be key factors for developing adaptive capacity.

High Urgency = understand impact and develop appropriate response within 3 yrs

Med. Urgency = initiation of action within 3-10 yrs

Low Urgency = action can wait 10 years, as there’s lots of capacity to ‘absorb’ impact

We can’t determine disaster risks with climate and exposure data alone… we also need to consider social vulnerability.

Vulnerability:the predisposition of aperson or group to beadversely affected

Exposure:the people, places or infrastructure that are affected

Climate Trends:the frequency and severity of the weather eventor climate trend

Assessing adaptive capacity

CommunityCharacterizations

100 Measures

10 themes

1. Health2. Education3. Demographics4. Sense of

community5. Governance6. Safety and

preparedness

7. Infrastructure8. Local economy9. Macro economy, 10. technology


Core measures

•Well-established and widely used

•The data is measurable and readily available (or could be collected through a community survey), and

•Meaningful in the context of the theme area and community climate adaptation


Study Limitations

• some indicators can’t be quantified

• qualitative information may not provide clear conclusions

• some qualities of adaptive capacity don’t have indicators

• there aren’t agreed on parameters indicating strong adaptive capacity

• What’s an appropriate reference?

• Research focuses on historical response


Hosting a conversation about socio-ec factors in the context of climate projections can add breadth to adaptation strategy, and help you identify and capitalize on actions that can benefit the community no matter how the future climate unfolds.

So what will help us host that conversation?



Closing

However good our future research may be,

we shall never be able to escape from the

ultimate dilemma that all our knowledge is

about the past,

and all our decisions are about the future.

Ian Wilson, 1975

Order / ControlThe place for management

Chaos / OrderThe place for leadership

Art of Hosting

Chaos / OrderThe place for leadership

1. What critical uncertainties face the organization?

2. What major strategic decisions do you have to make?

3. What do you need to know about the future in order to make these decisions?

http://climatechange.gov.ns.ca/content/impactsWorkshop



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Assessing Geological Hazards

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