Vulnerability of Water Utilities to Sea Level Rise

The Saco Water Resource Recovery Division (WRRD) provides sewer services to over 11,000 residents and 375 businesses. The WRRD treatment plant sits adjacent to the Saco River which is influenced by ocean tides. This leaves the plant vulnerable to flooding caused by storm surges and King Tides. These floods are expected to increase in frequency and severity due to sea level rise caused by climate change. If nothing is done, flooding will necessitate the complete replacement of the plant subject the community to other impacts. This presentation will explore the problem. 

The Water Resource Recovery Facility in Saco provides sewer services to nearly 12,000 residents and 400 businesses. The facility is vulnerable to sea level rise brought on by climate change due to its location on the banks of the Saco River. 

Rising sea levels in the Gulf of Maine lead to increasingly frequent severe storm surges. Storm surges amplify tides, making them rise higher than normal. High wind and heavy precipitation contribute. Acting to raise the water level on the ocean, storm surges will effectively back up rivers, causing their water levels to rise even miles upriver. Even though it sits nearly four miles upriver, Saco’s water treatment plant is vulnerable to flooding from storm surge events. Such surges can submerge the plant’s outflow pipe on the river bank and can cause water to seep up elsewhere on the site, potentially leading to overflows in the settling and treatment ponds. 

Such an incident has already happened in Saco. On December 14, 2019 a combination of heavy rain, melting snow, and an abnormally high tide swamped the treatment plant of the Water Resources Recovery Division. Combine with the normal inflow, the amount of water seriously stressed the facility. This was due to the fact that the plant's outlet relies on gravity to release its water. Put simply, more water was coming in than the plant could pump out. The managers are planning to install new pumping system which would alleviate the problem.

Nonetheless, this even seriously impact the plant's operations, forcing its operators to shut down the aereation system to contain solid matter in processing pools, thereby avoiding a serous sewage spill.

Sewage contains many contaminants which negatively impact the marine environment and public health. Toxic substances from commercial or industrial uses may be found in untreated water along with bacteria from human waste. Such waste poses other problems for the marine ecosystem. The nutrients in such waste leads to eutrophication which can cause harmful algae blooms.

The most noticeable impact from flooding at the treatment plant would be the closure of Old Orchard Beach and other beach areas along Saco Bay. This would not merely mean prohibitions against swimming. The contamination would sweep along the shore with the tides and lead to prolonger closures for the entire beach.

Discharges due to flooding will also render the shellfish normally harvested in Saco Bay inedible and can lead to die offs due to algae blooms.

AS the water level rises during flooding events, the discharge pipe and other systems at the facility become submerged, impeding operations. This can result in backups which will be felt by sewage service customers. In addition, the flooding can lead to discharges of untreated sewage and waster water into the river. This will result in the plant falling out of compliance with National Pollutant Discharge Elimination System (NPDES) regulations.

The NPDES is the permitting system for wastewater discharge by industry and municipalities under the Clean Water Act of 1972. When facilities such as the WWRD plant discharge more pollutants than they are permitted for, they face administrative fines, civil, and criminal action in courts. Under NPDES enforcement rules, fines can range from a one time $157,000 penalty to $32,000 for each day the facility remains out of compliance. These fines would likely result in increased service charges for sewer service.

The Water Resource Recovery facility is not the only thing that will be impacted by sea level rise driven storm surges. Businesses depend on the facility for sewer services. Because of that, sea level rise will impact the local economy. Households will also face service interruptions. Lastly, sea level rise will affect infrastructure such as roads and highways.

The map below shows the impact of different levels of sea level rise. Under current emission levels, Saco will likely see its water levels rise one foot over its current Highest Astronomical Tide (HAT). This will lead to regular tidal flooding of a substantial portion of the treatment plant at high tide. By the end of the century, the entire plant would be inundated at high tide.

Sea level is largely a by product of global warming due to emission of green house gases such as carbon dioxide, a product of combustion. Since the beginning of the twentieth century, ocean and sea levels have already risen between six to eight inches depending on the location.

Under current levels of emissions, sea levels will likely rise by a foot over the Highest Astronomical Tides. In some places, this is enough to inundate large parts of the shore while in others, this degree of sea level rise will lead to more damaging coastal storms and more frequent king tides. Unfortunately, the rate of sea level is accelerating due to glaciers melting faster than anticipated.

The answer to this question lies in an understanding of what sea level rise entails. Sea level rise represent more than the water creeping up the beach. Rather, sea level rise leads to a variety of consequential impacts. These include storm surge.

Storms bring high winds and those winds blow the water into the shore with greater force than normal. This leads to a run up of the tides, dramatically increasing their heights. This can flood coastal areas and even reach far inland as the high tides cause rivers to back up.

It is this storm surge that puts the water treatment facility at risk. As demonstrated December of 2019, a storm driven tide can impede the outflow from the plant. When combined with precipitation or melting snow, this can lead to flooding of the facility.

Storm surges arise from the intense energy of severe storms. Strong winds cause the tide to run up as they blow across the surface of the water and drive currents towards shore. Aggravating this effect, lower atmospheric pressure causes the water level in the storm's vicinity to rise. Meanwhile, storm winds drive higher waves which further raise the water level. When combined with rainfall, the sea level can rise far above normal during a storm. Beyond their impact on the shore, storm tides will travel quite far up rivers which empty out on the coast.

The Water Resource Recovery facility is not the only thing that will be impacted by sea level rise driven storm surges. Businesses depend on the facility for sewer services. Because of that, sea level rise will impact the local economy. Households will also face service interruptions. Lastly, sea level rise will affect infrastructure such as roads and highways.