December 4, 2017
Risk Analysis for:
Portsmouth Middle School, Portsmouth, NH
https://www.jcj.com/project/portsmouth-middle-school
There are many types of natural hazards that the City of Portsmouth considers in planning and constructing. The major hazards include:
• Flooding
• Increased precipitation
• Hurricanes, and other high-wind events
• Severe winter weather
• Wildfires
• Earthquakes
• Coastal storms
• Sea level rise
The following report will the address the potential risks these hazards pose to the Portsmouth Middle School and the mitigation tactics in place to prevent serious loss in the event of a natural hazard.
In addition to natural hazard mitigation methods, all construction in the city of Portsmouth must comply with building codes:
• International Building Code
• International Fire Code
• International Plumbing Code
• International Mechanical Code
• International Energy and Conservation Code
• National Fuel Gas Code
• National Electric Code
• Life Safety Code
Flooding and Increased Precipitation: Flooding is caused by the combination of increased water levels where water does not typically stand and failure to drain or remove the water. Flooding is most likely to occur in the spring because precipitation levels generally increase and snow melts in the rising temperatures. Downtown Portsmouth is also at risk of flooding due to rise in sea level and storm surges.
The Portsmouth Middle School is specifically at risk of flooding because of its proximity to the South Mill Pond and the Piscataqua River, but the building has been designed to mitigate flooding. In the event of flooding, the City of Portsmouth does participate in the National Flood Insurance Program so that rebuilding will be possible. Being part of NFIP also requires the City to take necessary measures in flood prevention mandated by the Federal Insurance and Mitigation Administration and the Federal Emergency Management Agency.
As visible on the second image on the right, the building lies within the blue area (1% annual chance flood hazard) and the orange area (.2% annual change flood hazard) on the FEMA National Flood Hazard map. Methods in place include proper drainage systems, high content of vegetation surrounding the building and a partially green roof.
With proper drainage systems, large influxes of water are redirected away from the building. Updated drainage systems surrounding the Middle School includes preventing back flow, installing new sewers, and refitting small pipes with larger ones.
Because of the School’s proximity to the South Mill pond, the pond’s water level can be manipulated. In the event of great precipitation or sea level rise, the pond can be kept empty or not fill completely so excess water can fill it. Using water flow controls limits the possibility of the water level rising to the Middle School and limits the possibility of the School to be unable to drain. Finally, the School has been created with a partially green roof, meaning the roof is partially covered in vegetation which absorbs rainwater rather than redirect all of it into the drainage system. Lastly, in the event the Middle School does experience flooding, the City of Portsmouth has drainage pumps that can be used in the unfinished basement.
Hurricanes and other high wind events: The City of Portsmouth includes tornadoes, Nor-Easters, lightning and thunderstorms in the other high wind events category. The City is at high risk of experiencing hurricanes and nor-easters, but does not consider tornadoes as high risk. Hurricanes are caused by warm air rising near the equator that creates an area of lower air pressure below. Air from surrounding areas fills in the low pressure area, but then begins to heat up from the warm ocean and rises too. As this continues to happen, the air swirls in building speed creating the hurricane (http://www.thenewsminute.com/article/how-do-hurricanes-form-know-nasa-scientists-68187).
Hurricanes typically cause the most damage to power lines, shingled roofs, chimneys, trees, mobile homes, sewage pumps stations, cell towers, parks and harbors. Between 1635 and 2015, 14 hurricanes have impacted New Hampshire, so the City finds it of high necessity to be prepared(http://files.cityofportsmouth.com/fires/Portsmouth_HazMit_May2017.pdf). The Middle School is at lower risk because it is not close to many trees and the power lines are majorly underground. The School is equipped with high grade windows and doors, so flying debris will not break glass. The shingled roof section of the school was recently redone, so its ability to resist destruction is increased. The major threat posed by the hurricane on the school is that transporting students to and from school as part of the typical operation is risky. The best way to mitigate loss or damage in this situation is to delay or cancel operations during hurricanes.
Severe Winter Weather: This category includes ice storms, freezing temperatures, and blizzards. These are all typical events during winter because of the decreased temperatures which result from the Northern Hemisphere temporarily distancing from the sun. The City of Portsmouth encourages wind-resistant roofs and light frame construction to mitigate damage.
Outside of transportation, winter weather only becomes hazardous when it occurs in extremes.
Ice storms are notorious for causing fallen power lines. The Middle School is not surrounded by power lines, so danger related to crossing fallen power lines is not possible. Lack of electricity will be detrimental to the daily operation of the school, but will not be problematic for an extended period of time because the school is equipped with generators, as well the building is heated by gas so the possibility of cold temperature related issues, like health of the population inside the building and freezing pipes, is considerably lowered.
Blizzards are snow storms with snow fall exceeding 30 inches. This type of snow storm usually occurs once per winter. The only major risk posed by blizzards to the school is the potential of roof collapse with lots of heavy snow. To prevent roof collapse, the new section of the school has an easily accessible roof so the snow can be removed. Another hazard associated with snow storms is the increased likelihood of vehicle collisions. Because the road wraps around the building, it is very unlikely that a sliding vehicle would be moving in the direction of the building.
School operations should be delayed or cancelled if severe winter weather occurs to avoid potential casualties.
Wildfires: Wildfires are a risk in parts of Portsmouth, but are not considered a hazard near the Portsmouth Middle School because of the lengthy distance between the school and woodlands.
Earthquakes: Earthquakes are the result of tectonic plate movement. Portsmouth, NH is not located within close distance of any fault line, and therefore has a moderate risk of damage due to earthquake, as this table illustrates:
In the event of a very strong earthquake, moderate damage may occur and affect the brick structure of the building, water and gas lines. There were no preventative measures taken in constructing the building to lessen the extent of damages caused by earthquake, as serious damage is unlikely. If damage occurs, work will need to be done to fix the brick structure and repair the gas and water lines. The City could invest in more earthquake resistant building materials, but this is not recommended as the cost of replacing the entire building’s outer walls would be high and the likelihood of extended damage is low.
Coastal Storms and Sea Level Rise: Coastal Storms are typical weather events experienced in seacoast New Hampshire. Coastal storms can cause damage with extreme storm water runoff and storm surge. Sea level rise is caused by increased global temperatures that cause glacial melt and expansion of ocean water molecules. The image below depicts which areas will be affected by extreme storm surge (100-year/1% chance storm event) and sea level rise up to 6.3 feet.
The Middle School does not have preparative measures in place for such storms and sea level rise beyond its infrastructure to mitigate flooding. Measures that could be taken are purchasing more powerful large-capacity pumps for the City that can assist in flood water removal. Though costly, prices range from $2,000-$25,000, the pumps would prevent foundational damage to the Middle School and can be used in other public buildings if necessary. In addition, flooding caused by storm surge is covered by FEMA insurance.
To mitigate damage from sea level rise, the City is currently in the works of creating a long-term plan to prevent sea level rise in vital areas using water redirection techniques and sea walls. Mitigating damage from rising sea levels is expensive, but given the population in and economic stimulus from areas in low- elevations in Portsmouth makes such projects necessary.