Presentation on theme: "Sea Level Rise 2014 City Council Update"— Presentation transcript:
1Sea Level Rise 2014 City Council Update City of Olympia | Public Works, Water Resources March 2014Hello I am Eric Christensen, a water resources engineer with the City’s Public Works Department.I am here to discuss our understanding of the processes of sea level rise and what they mean to Olympia. My discussion will cover:Our history preparing for SLRThe current potential for flooding in downtownThe most recent SLR projectionsThe processes contributing to sea level riseThe mechanisms by which we floodThe measures needed to address floodingAnd the progression of implementing those measures in preparation for SLRPLEASE ASK QUESTIONS AT ANY TIMECity of Olympia | Capital of Washington State
2Sea Level Rise in Olympia Olympia has been concerned with climate change and sea level rise since Since then a series of assessment reports have been prepared.
3Existing Flooding Extents – 10-year event This starts SLR LoopBased on our most recent report titled Engineered Response to SLR, this animation shows the areas of downtown that are currently vulnerable to flooding during 10, 50 and 100 year return events. As the maps show, significant areas of downtown can currently be expected to flood. A 10-year event can be expected to flood roadways and result in inflow to the LOTT WWTP through the combined sewer system. Temporary barriers and tide gates are needed if we are to protect structures against the 50 and 100-year events.
4City Policy - 2010 Protect downtown. Understand the implications of 50 inches of sea level rise.Use opportunities for new public and private investments to prepare for sea rise.Seek opportunities to maintain control of valuable shoreline.Our vulnerability to flooding is well recognized and our understanding of the implications of sea level rise increases incrementally each year. We have been moving forward with the policy established by Council in Key points of that policy were to protect downtown and prepare for 50 inches of SLR.
5International Panel on Climate Change National Research Council In addition to local studies, several national and international studies have been prepared. Key amongst those are:IPCC Assessment ReportsNational Research Council sea level rise evaluation of the West Coast 2012
6Sea Level TrendsSLR has been an observable trend. Over past century tide gauges indicate sea levels have risen about 7 inches. But over the last 20 years, satellite data indicates that rate has accelerated to nearly twice as fast as it has been over the last 100 years. (from 1.7 mm/yr to 3.2 mm/yr)
7Global Sea Level Rise Projections The big questions are still How much? and How soon?Results of IPCC’s 5th Assessment Report project sea level rise of between 11 and 39 inches by 2100 which is more than 50% percent higher than the previous IPCC report in (7.1 to 23.2 inches by 2100). The key difference is the previous projections did not take into account the possibility of rapid ice flow from Greenland and Antarctica. Ice sheets are important because they store enough water to potentially raise sea levels more than 200 feet.There is a good deal of variability between studies performed to date. As this chart indicates there is good confidence that there will be less than 9 inches of SLR by 2030 and less than 19 inches by Beyond that the level of uncertainty increases.
8Processes influencing sea level Primary ProcessesThermal ExpansionMelting GlaciersMelting Ice SheetsTerrestrial StorageAdditional ProcessesWeatherVertical Land MovementSea level is rising because the ocean is warming which increases ocean volumeAlso because ice sheets and glaciers are melting andA reduction of water storage on land (groundwater, wetlands, etc)Additional factors include: Vertical land movement and Weather– Tectonics, Glacial isostatic adjustment (rebound), Groundwater and hydrocarbon mining leading to land subsidenceWeather
9Sea Level Rise – Relative Contributions of the Various Processes Assuming greenhouse gas stabilized near current levelsThis slide shows the projected relative contributions to total sea level rise of most of the processes I’ve just mentioned. Note that thermal expansion, ice sheet dynamics and glacial melt are the largest contributors to sea level rise. Ice sheet flow and land storage are becoming better understood than in previous assessments and account for the largest increase in recent projections.
10Projected Flooding Extents – 0-feet sea level rise This starts SLR LoopThis animation shows the extent of flooding to be expected with sea level rise. Significant infrastructure including permanent barriers, consolidation of storm drainage systems and pump stations will be necessary to prevent flooding as sea levels rise.
112013 IPCC Report Key Findings Global mean sea level rise will continue for many centuries beyond 2100, with the amount of rise dependent on future emissions.If Greenhouse gases are curbed, sea level rise will be less than 1 m by 2300.If Greenhouse gases are not curbed, sea level rise may be up to 3 m by 2300.Larger sea level rise could result from ice sheet flow.Near-complete loss of the Greenland ice sheet will occur with warming of between 1°C and 4°C.SLR will continue well beyond 2100 and it is virtually inevitable that our ancestors will be faced with meters of SLR in the not too distant future.The amount of SLR will be based on our control of Greenhouse gasesIce sheet dynamics have the greatest potential to change SLR projectionsA raise in temperature of between 1 and 4 degrees will lead to the complete loss of the Greenland ice sheet which could account for up to 24 feet of SLR over several centuries.
12Vertical Land Movement TectonicsSea level rise will vary regionally based on whether the land is rising or sinking. A key factor is tectonic activity. Along the west coast we have an active coastline that we know is moving. In Oregon and Washington along the Cascadia subduction zone, the land is generally rising.
13Vertical Land Movement TectonicsGlacial isostatic adjustmentHowever, in the south Puget sound there is evidence that the land is subsiding most likely due to rebounding from the Cordilleran ice sheet (12,000 years ago). In Olympia, along the former margins of the ice sheet the land is subsiding and not rebounding. (Latitude 47)
14Vertical Land Movement Monitoring Olympia’s elevationsThe Washington State Reference Network monitors fixed regional global positioning stations. Short term results indicate the Olympia vicinity is subsiding 0.5 to 1 inch per decade (1.3 to 2.4 mm per year). Vertical land movement is clearly one of the greatest uncertainties for SLR in Olympia.
15Importance of El Nino Events Climate change will also affect weather patterns which in turn can have significant influences of sea levels.For instance, during El Nino events, sea levels in the north Pacific can be elevated several inches for several months due to decreased atmospheric pressure.In short term events, especially in El Nino years, the water levels have exceeded mean sea levels projected for 2100.Thus for the next few decades El Nino events are a greater hazard than the climate driven rise in sea level.It is very likely that as sea levels continue to rise, El Nino events will become greater in magnitude and increase in frequency.
16Importance of Weather Fiddlehead Marine - December 17, 2012 The tidal event on December 17th, 2012 was a good example of the impact of weather on water levels. On that day, due to the low atmospheric pressure, the actual tide was about a foot higher than the predicted tide. A decrease in atmospheric pressure of 1-inch mercury causes 13.6 inches of rise in tidal elevation.Fiddlehead Marine - December 17, 2012
17Tools for Predicting Tides Tides are predicted years in advanceAtmospheric models forecast pressure weeks in advanceNOAA and Emergency Management Organization WarningsStream gages on the Deschutes RiverWe are most vulnerable to flooding only during relatively short-term (hours) tidal events and those events are predictable. Fortunately we have excellent tools in place to help us predict these events. City staff as well as regional emergency management personnel monitor forecasts regularly
18Tacoma NOAA Real Time Tide Data In addition, we are able to track the real time tide gage in Tacoma to give us more confidence in what impact barometric pressure and wind is having on our tides.
19Flooding MechanismsInundation of Budd Inlet and Capitol Lake ShorelinesPipe Backflow from Budd Inlet and Capitol LakeTerrestrial RunoffOur primary vulnerabilities to flooding are:(Deschutes and Moxlie)
20Inundation of Budd Inlet and Capitol Lake Shorelines Shoreline flooding is simply what you would expect. Tides, storm surge and wind and waves all can contribute to overbank flooding
21Inundation of Budd Inlet and Capitol Lake Shorelines An example of shoreline flooding was observed when tides came in over the parking lot and Sylvester Street at the Oyster House in December 2012.(Highest tide in at least 20 years. More than a foot higher than predicted due to low atmospheric pressure. )Oyster House - December 17, 2012…17.6 Foot Tide
22Inundation of Budd Inlet and Capitol Lake Shorelines Solutions for shoreline flooding are temporary barriers, sea walls, levees, sheetpiling and potentially elevating the land. The City will likely install a combination of all of the above.
23Temporary Flood Barriers Initially, it is believed we can protect downtown from the current 100-year flood and slightly beyond using temporary barriers such as water-filled bladders.
24Temporary Flood Barriers - Locations Locations where temporary barriers will be needed are depicted in this image. Those locations are primarily along the eastern shores of West Bay and Capitol Lake.
25Barrier Locations – 0.25 ft sea level rise Permanent barriers will be needed before sea levels rise ¼ foot. This image depicts anticipated locations of those barriers.
26Barrier Locations – 0.5 ft sea level rise and beyond As sea levels rise ½ foot and beyond additional barriers will be required on the eastern side of the peninsula. The height of these barriers will need to be increased, but the locations will not need to change with sea level rise up to 50”.
27Pipe Backflow Flooding The next flooding mechanism I will discuss is backflow flooding. This slide provides an animation of backflow flooding. Note that even with a sea wall, we would still be vulnerable to flooding due to existing pipe conduits.
28Pipe Backflow Flooding The solution to backflow flooding is to install a valve or tide gate in the appropriate places in the drainage system.
29Pipe Backflow Flooding An example of backflow flooding can frequently be observed in front of Budd Bay Café. This photo demonstrates the vulnerability of downtown. The water in this photo is marine water that flowed through the drainage system and not over the shoreline.Budd Bay Cafe
30Pipe Backflow Flooding 112 known outfalls to Capitol Lake and Budd Inlet within the city limitsThere are 112 known piped outfalls connected to Capitol Lake and Budd Inlet
31Pipe Backflow Flooding Of those piped outfalls, 36 are susceptible to backflow flooding20 City –owned9 State-owned5 Port-owned2 Privately-ownedOf the 112, 36 are susceptible to backflow flooding. Several already have valves that need to be maintained. At least 20 additional valves will be needed to prevent flooding if barriers are installed.
32Capitol Lake and East Bay The 2 areas currently most susceptible to backflow flooding are Capitol Lake and a 6+ block area west of East Bay.A valve and pump system have been successful in preventing flooding in the recent past in the vicinity of 7th and Water Street, but have limited capacity.A new valve is needed on a 24-inch pipe near Marine Drive to prevent flooding near East Bay.
33Backflow Prevention Devices This slide depicts typical backflow prevention devices including flap gates, gate valves and duck bill valvesFlap tide gates & Gate valvePinch valve “duck bill”
34Terrestrial Runoff Flooding Terrestrial Runoff Flooding occurs when large precipitation events result in flows that exceed the conveyance system capacities. Olympia is most vulnerable to runoff flooding from the Deschutes River and Moxlie Creek.
35Inundation of Budd Inlet and Capitol Lake Shorelines Tides, backflow and Deschutes River runoff all combine to make flooding at Capitol Lake our greatest vulnerability. The State’s management of the 5th Ave dam plays a significant role in preventing flooding in downtown. City staff also manage valves and pumps to prevent flooding between 5th and 7th Avenues and Water and Columbia Streets.Capitol Lake
362014 Work Plan Tasks Survey shoreline elevations Survey vulnerable structure elevationsIdentify combined sewer catch basins vulnerable to floodingPurchase temporary barriers and practice placementOur proposed 2014 work plan tasks include:
37Additional Short-term Tasks Design strategic tide gatesModify drainage system for the Capitol Lake to eliminate need to pump 20-acre basinInvestigate the permeability of downtown soilsAdditional short term tasks will be performed over the next 5 to 6 years using funding allocated in the current CFP. These tasks will include:
38Medium-term Tasks (0.25 to 0.5 feet of sea level rise) Modify elevations of Heritage ParkInstall permanent flood barriers on western shore of peninsulaConsolidate peninsula drainage systemsDisconnect flood-prone streets from the Moxlie Creek drainage systemPurchase pumps to handle downtown runoff during high tidesMedium term tasks are significant in scope and cost. These tasks are expected to cost $13 million or more in today’s dollars. Barriers will be designed for 1-foot of SLR with plans for future expansion.
39Long-term Tasks Raise barriers building on existing foundations Construct pump stations for consolidated drainage systems and Moxlie Creek.Long-term infrastructure including raised barriers and necessary pumps stations are estimated to cost more than $50 million.In the long term, something to understand is that several meters of SLR are inevitable. Fortunately, unlike other communities in Puget Sound and locations like Louisiana and Florida, we are at the end of a narrow and shallow inlet, we can engineer a solution. It has environmental consequences, but we can save the most historical community in Thurston County.We do not live in a natural environment. Much of downtown is constructed on fill.
40City of Olympia | Capital of Washington State Eric Christensen City of OlympiaIn conclusion I want to say that although we are not able to predict the magnitude and timing of sea level rise, we do understand downtown, its flooding potential and appropriate actions to take.City of Olympia | Capital of Washington State