CE 451: Water Resources Engineering

Articles and information related to the floods in Rhode Island during March of 2010

Summary:

Rhode Island encompasses 1,212 square miles, 13 percent of which is inland water. This inland water encompasses 357 freshwater ponds, lakes and impoundments and amounts to an area of 29 square miles (Rhode Island Water Resources Board, 1970); the saline waters of Narragansett Bay account for the remainder. Quantitative measures of both floods and droughts in Rhode Island can be obtained from records of precipitation and streamflow (streamflow generally being favored in this area). Systematic collection of streamflow records in Rhode Island began in 1929 when a continuous-recording gage was installed in the Blackstone River at Woonsocket. These measurements were expanded upon between 1939 and 1941 when eight similar gages were installed on other major rivers.

Rhode Island’s climate is primarily continental. Annual precipitation ranges from about 40 inches near Narragansett Bay to 50 inches in the northwestern hills. At Providence, precipitation records spanning 166 years indicate a range from 25.4 inches in 1965, which is 56 percent of normal, to 65.1 inches in 1972, which is 144 percent of normal. Large floods are rare in Rhode Island but are not specific to any season when they occurDuring the months of March and April 2010 the state of Rhode Island experienced very heavy rainfall that resulted in disastrous floods. The combination of a strong El Nino southern jet stream and a “Omega Block” over the North Atlantic led to a series of three heavy rainfall episodes (storms) each of which compounded the damage for the next storm. The first and last of these three storms caused extensive flood damage within the Northeast Corridor including the States of Connecticut, Massachusetts and Rhode Island.

The moisture patterns shown above all eventually contributed to the heavy rains that pummeled Rhode Island.

Weather History for March:

From the graphs above we can see that during the month of March Rhode Island experienced a large peak in rainfall on three separate occasions. The peak precipitations were; 1.37 inches on March 13th, 1.57 inches of March 23, and 4.44 inches over the course of March 29th and 30th. The precipitation high for the month was 9.19 inches.

The image above shows the storm total rainfall for the March 29 – 30 episode. This storm lasted approximately 36-hours and had a preliminary return frequency based on rainfall of 75 years. However the fully saturated soil conditions combined with many rivers that were near flood stage at the start of the storm resulted in flows on some smaller streams and rivers that exceeded 500 years in many locations.

Damage from these storms was compounded by a single primary factor, lack of sufficient recovery time for rivers to recede between each episode. Shown in the figure below is a 31-day river hydrograph for the Pawcatuck River at Westerly, Rhode Island which shows that the flow on this river did not return to previous levels after each heavy rain episode. With each successive storm, the flow (represented by the blue line) within the Pawcatuck River basin increased by approximately 600 CFS and 1,000 CFS respectively. The earlier storms on March 13, and 23, resulted in a net increase to flows of 1,600 CFS. This increase in flow combined with fully saturated soil conditions greatly aggravated the severity of the flooding on March 29 – 31.

We can also see from the image below (which shows streamflow) that the majority of RI was above the 90th percentile mark and a good portion of the state experienced streamflow even greater than this benchmark.

Information and graphs of the March Storms and floods can be found at http://ma.water.usgs.gov/water_statement/2010_03/index.html and
http://www.stonington-ct.gov/Pages/StoningtonCT_EmerNews/029D1341-000F8513.1/MARCH%20STORMS%20OF%202010a.pdf

Weather History for April 2010:

From the graphs above we can see that during the month of April Rhode Island again experienced a large peak in rainfall on three separate occasions. The peak precipitations were;.81 inches on April 8th; .43 inches combined on April 16th & 17th; and .16 inches on April 25th. The precipitation high for the month was 1.74 inches. The first of these periods of heavy rainfall, combined with the heavy rains of March, lead to very severe flooding.

From the hydrograph above and the corresponding key we can compare the flow at the Pawcatuck River at Westerly, RI with flow over the course of the last year. The black line represents actual flow while the colored bands represent each of the percentile classes respectively. We can see that the flow in March and April of 2010 was not only greatly higher than that of the previous year, it was also well above the 90th percentile for flow in that month in general.

We can also see from the image below (which shows streamflow) that more than half of RI was above the 90th percentile mark while the majority of the remaining area was between the 76th and 90th percentile marks.

Information and graphs of the April storms can be found at
http://ma.water.usgs.gov/water_statement/2010_04/index.html and

Hydropgraphs for any month can be seen at
http://waterwatch.usgs.gov/index.php?sno=01114500&yr=2010&dt=dv28d&btnGo=GO&m=sitedur&s=&sno2=01114500 by entering the desire year and period.

Results and Aftermath:

The rivers most significantly affected by the intense rainfall during March and April of 2010 were the Pawtuxet and Blackstone rivers. The Blackstone River has been regulated since 1961 by West Hill Reservoir in Massachusetts, which has a storage capacity of 542 million ft3 (cubic feet). The South Branch Pawtuxet River has been regulated since about 1875 by Flat River Reservoir, which has a usable capacity of 250 million ft3. The flooding which occurred due to overflow at these two rivers and others during the month of March was qualified as a 100 year flood. During the month of April flooding was so great that it once again qualified as a 100 year flood. This statement is staggering when we realize that a 100 year flood is the flood level which has a 1% chance of occurring during any given year. Taking that into account, the chances of having two 100 year floods only two weeks apart is infinitesimally small. And it is partially because this second flood was so unexpected that it was able to do so much damage. At the Cranston gauge on the Pawtuxet water levels were higher than any recorded dating back to 1939. The gauge registered a flow of 14,000 cubic feet per second Tuesday night, compared with the last record flood two weeks prior of 5,000 cubic feet per second. Normal flow rates range from 750 to 1,000 cubic feet per second according to Ed Capone, service coordination hydrologist at the Northeast River Forecast Center. On the Blackstone River flooding was compared to that which occurred during 1955 during the hurricanes Connie and Diane. The Pawtuxet River, which runs through Cranston (one of the most heavily affected areas), crested at 20.79 feet on Wednesday, March 31st, nearly 12 feet above flood stage, according to the National Oceanic and Atmospheric Administration.

Perhaps the most drastic consequence to result from the severe flooding was the complete desecration of Rhode Island’s sewerage systems. Half a dozen sewage systems were completely overwhelmed and compromised by the most destructive flood Rhode Island has ever experienced. This lead to huge ramifications for the state for both public health and economic stability. Janine Burke, executive director of the Warwick sewage authority said the events had set them “back a century in wastewater treatment in the city of Warwick”. The river breached the levee protecting Warwick’s sewer plant and submerged its pumps as seen in the diagram below.

These events caused contaminated water to flow out of drains and faucets all over the state, entering houses and compromising drinking water. Residents were advised not to drink any water without boiling it first to kill bacteria.

The damage done by the floods in Rhode Island was not limited to the sewage system. Interstate 95, a major east coast highway was shut down for days, making transport virtually impossible. Traffic jams snaked for miles around as a result, halting business in countless areas. In Warwick alone about 2,500 businesses and homes were evacuated, city press secretary Sue Baker said. About 200 of them had been flooded for the second time in two weeks, she said. According to FEMA’s preliminary damage report 455 residences were affected with over 100 experiencing major damages and over 300 subject to minor damages. The Total Individual Assistance cost estimate amounted to just over three million dollars. A spokesman for National Grid Energy Services said 12,000 to 14,000 customers were without electricity in the Cranston area, where a substation was underwater. In Westerly, Rhode Island, another 9,600 customers were entirely without electricity.

The two floods will also greatly affect Rhode Island’s economy. The storms were “like a kick in the teeth” for a state already suffering from double-digit unemployment said Governor Donald L. Carcieri. One major impact can be seen in the flooding of the devastated Warwick Mall, the third-largest shopping center in Rhode Island. Parts of the mall were flooded with up to three feet of water, and its 70 stores remained closed indefinitely. As can be seen in the picture below, the mall’s parking lot was completely submerged in feet of water while the interior was completely flooded. Countless employees at the mall and other retail areas will be out of a job, thus contributing further to the already escalated unemployment rate. A Red Cross official said the flooding may affect as many as 200,000 of Rhode Island’s roughly 1 million residents, and compared the impact to that of a major hurricane. Rhode Island already has a $220 million budget shortfall for the fiscal year that ends June 30 and faces a $427 million deficit for next year.

On March 30, President Barack Obama signed an emergency declaration for Rhode Island after Gov. Don Carcieri requested the move, putting Federal Emergency Management Agency (FEMA) officials in place to work with state and local responders, and to allow individuals and businesses to apply for federal funds for losses and damages. Rhode Island households and businesses affected by severe storms and flooding beginning March 12, 2010, have received $50,921,890 in approved disaster grants and loans, according to the Federal Emergency Management Agency and the U.S. Small Business Administration. FEMA has completed 21,757 inspections and had 190 inspectors in the field during the peak of emergency response. By April 4th The Federal and Rhode Island Emergency Management Agencies (FEMA and RIEMA) had opened Disaster Recovery Centers (DRCs) in Cranston and Warwick for Rhode Islanders to get face-to-face assistance from disaster specialists with DRCs throughout other areas of the state opening within days. By April 9th FEMA announced that all five disaster-designated counties in Rhode Island were eligible for disaster Public Assistance for losses related to the floods. Assistance was been made available to Bristol, Kent, Newport, Providence and Washington Counties via an add-on to the presidential declaration authorized by President Obama on March 29, 2010. Local governments and certain private nonprofit organizations in these counties are eligible to apply for federal funds to pay 75 percent of the approved cost of debris removal, emergency services related to the disaster, and repairing or replacing damaged public facilities, such as roads, buildings and utilities. These assistance efforts are crucial for the state to be able to recover from the economic effects cause by the storms.