Intense Precipitation in Acadia National Park

The damage caused by increasingly strong storms because of climate change.

Climate Change and Precipitation

In Acadia National Park, climate change is causing rain events to become larger, more intense, and more localized (Star, et al., 201). Over the last half-century, "precipitation amounts have increased (Zhang et al. 2007), particularly in fall due to heavier rainfalls'' (Star, et al., 201). Projections of future change in climate from the IPCC indicate "increased precipitation under all emissions scenarios'' (Gonzalez, 2014). This will likely be a "doubling of the frequency of five-year storms from 2000 to 2100" (Gonzalez, 2014). The likelihood of "North Atlantic hurricanes, which can produce storms that track up the coast to the area of Acadia N.P" is also increasing (Gonzalez, 2014).

These intense storms are especially a problem here because of the geology and topography of Acadia National Park. The map below highlights the rain runoff potential on the island. The map combines permeability (bedrock surficial geology and areas of bald granite communities of vegetation) and slope (slopes greater than 15%) characteristics.

As seen on this map, exposed bedrock and steep slopes cover much of the park. This results in fast runoff of water during a rain event.

The summer of 2021 saw two major rain events that the park describes as "megastorms". On June 9th and on July 20th, it rained at a rate up of up to 4 inches per hour.

This radar is measured in decibles. 20 dBZ  light rain begins, 35 dBZ is moderate rain, 50dBZ is heavy rain, and at 60 to 65 dBZ 1" (2.5 cm) diameter hail can occur.

The looping video below shows the storm of the evening of the 20th of July. The radar images are taken from the NOAA National Center for Environmental  Information website. 

The legend on the map is inches of precipitation per hour .

Carriage Road Washouts

The carriage roads and culverts and drainage ditches of the park were built around 100 years ago. Park infrastructure, although well built and designed for the time was not designed to withstand the intensity of precipitation caused by climate change (2021, Road to Recovery?). "These changes [in climate] have affected infrastructure, with larger rain events taxing older infrastructure. (Star, et al., 201)". "Severe storms are causing erosion and an increase in the amount of maintenance needed for the park (Trotter, 2018)" (Cunningham et al, 2019). "Heightened storm surge and heavier rainfalls are also problematic for Acadia National Park, which may wash away the historic carriage roads and hiking trails'' (Cunningham et al, 2019). During an intense rain event, water flows quickly down steep slopes of low permeability surficial geology. The runoff is further intensified by the historical culverts and drainage ditches that concentrate the flow. This is not only a major problem for the roads and trails of the park, but also for the forests, wetlands and streams (2021, Road to Recovery?). The gravel and crushed stone sediments washed off of the roads covers large areas of the forest floor and stream bottoms. This is detrimental for plant and animal health and habitat. The stone is also mostly of a type not native to the island, and so changes the chemistry of the land and water.  This event occured on June 9th 2021, when a record breaking five-plus inches of rain occured in less then three hours. Over 400 tons of material was washed off of the cariage roads. The damaged caused, resulted in over $1.5 million in repair costs for the park. (2021, Road to Recovery?).

Damage to Acadia's historic carriage roads from a severe strorm on June 9, 2021. (NPS Photo by Heather Cooney)

The forest floor is covered in sediment that has washed off the carriage road. This causes damage to the forest as well as the park infrastructure

Park natural resource management staff, standing atop a large amount of gravel washed into the woods from the carriage roads, discuss how to assess the natural resource damage from the June 9th storm. (NPS Photo)

"[n spring 2022] One preliminary result is we observed more than double the tree seedlings in the unimpacted forest floor, compared with impacted by deposits or scour", said Jesse Wheeler, Biologist Vegetation Program Manager at the park.

A map made by the park. I have it here because it shows the percent of impact on the different locations, and the sections of carriage roads that have been eroded.

The map on the left is layers created by the park, showing a layer of purple polygons of areas where gravel washed off the carriage roads and into the forests or streams and a layer of yellow points where the park installed straw wattles to to mitigate the damage after it began to occur.  On the right is the map of permeability and slope I created shown at the beginning of the story. It can be seen that the most damage occurred on sections of the carriage roads that are downhill from large slopes of low permeability. The park has only focused on this one area, although similar damage has likely occurred in other areas as well.

Potential Carriage Road Washouts

To further explore this issue, I mapped areas sections of the carriage roads that are at risk. I did this by using my runoff map of permeability and slope and selected sections of the roads that are downhill from large slopes of low permeability. I ranked the risk level low, medium, or high based on my interpretation of these map layers.

Beaver Dam Rupture

Beaver dams are the other "infrastructure" in the park that were not designed with a changing climate in mind. While this is a natural occurrence, it is being exacerbated from climate change. The intense rain events can cause the beaver ponds to suddenly overflow the dams and cause the dams to break. This can release a huge amount of water very quickly causing flooding and erosion downstream. On July 20th, 2021, The dam at the upper wetland above Breakneck ruptured. This was caused by an intense storm a few hours earlier. The water let loose flowed down a steep slope, across the Breakneck Road, into the lower wetland, and then down Breakneck Brook. This major flooding dug a deep channel into the forest floor, washed out many trees, and caused a landslide of boulders that buried Breakneck Road. Sarah Hall and students (including me) have been mapping the area to record the impact of this event. Below is a map of the area. You can swipe between the before and after.

Sarah Hall

where the dam used to be, loooking upstream at where the pond drained - reconstruction of the dam has begun by beavers, ans a portion of the old dam can be seen on the right - Sarah Hall, August 1st 2021

Boulders and cobbles cover the Breakneck Road where the landslide occured - Sarah Hall

Water flowing out of the upper wetland after the beaver dam ruptured carved a channel though the forest floor and took out many trees.

Potential Beaver Dam Failure

The geography, topography, and geology of Mount Desert Island make it especially susceptible to problems with beaver dams failure. The steep slopes and large amount of exposed bedrock cause for fast runoff. Many dams store water at high elevations and above steep slopes. And there is human infrastructure close downstream of nearly all of the dams on the island. Another aspect is that beavers were only re-introduced to the island in the last one hundred years. Because of this, infrastructure on the island was not designed to work with them, and the island does not have much history or data of beavers and modern infrastruc coexisting. However, now there are many beavers on the island. There are a lot of beaver dams that may break and cause similar things to what happened at breakneck in the future. To map this, I looked closely through detailed aerial imagery of the island and clicked points for where I was able to identify beaver dams. I am sure that I missed many.

Below are two examples of how beaver dams appeared on the real imagery

Some are large and holding back a large body of water. This would be very destructive if broken.

Others are a little less clear and are a series of much smaller dams. Even though a dam like these breaking would not cause much damage, I included them on the mapto demonstrate the prevalence of beavers.

Because the rain is also becoming more localized, this scene show what could have happened if it had rained in a differnt spot, causing a differnt dam to break.

There is currently no study of the beavers in Acadia National Park. I belive that there should be, as they case profound impacta on the landscape, as well as the potential hazards to human safety and infrastructure that they represent.

Anecdata

Evidence of Intense Storms: Mt Desert Island, Maine

This Anecdata page has neen chreated by Sarah Hall to allow people to document the increasing damage caused by intense storm events on Mount Desert Island. Participants may use photos and descriptions to document changes to infrastructure or landscapes during storm events. This may include: road washouts, erosion of soil or stream banks, flooding, sedimentation, rockfall, etc.

Data can be added directly to this Anecdata.org web page created by Sarah Hall to continue adding to this ongoing project

This radar is measured in decibles. 20 dBZ  light rain begins, 35 dBZ is moderate rain, 50dBZ is heavy rain, and at 60 to 65 dBZ 1" (2.5 cm) diameter hail can occur.

Damage to Acadia's historic carriage roads from a severe strorm on June 9, 2021. (NPS Photo by Heather Cooney)

The forest floor is covered in sediment that has washed off the carriage road. This causes damage to the forest as well as the park infrastructure

Park natural resource management staff, standing atop a large amount of gravel washed into the woods from the carriage roads, discuss how to assess the natural resource damage from the June 9th storm. (NPS Photo)

A map made by the park. I have it here because it shows the percent of impact on the different locations, and the sections of carriage roads that have been eroded.

where the dam used to be, loooking upstream at where the pond drained - reconstruction of the dam has begun by beavers, ans a portion of the old dam can be seen on the right - Sarah Hall, August 1st 2021

Boulders and cobbles cover the Breakneck Road where the landslide occured - Sarah Hall

Water flowing out of the upper wetland after the beaver dam ruptured carved a channel though the forest floor and took out many trees.

Some are large and holding back a large body of water. This would be very destructive if broken.

Others are a little less clear and are a series of much smaller dams. Even though a dam like these breaking would not cause much damage, I included them on the mapto demonstrate the prevalence of beavers.