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Connecticut Streamflow Overview and Drought Conditions

Connecticut Streamflow and Groundwater Overview

Know Your Flow!

Click on any graphic below for more information
 [color code for]  [color code for]  [color code for] [color code for]  [color code for]  [color code for]  [color code for]               [color code for]        
   High Flow     Low Flow        Not Ranked
CT Current Streamflow. Click to go to source page.
Streamflow in CT Now (click to go to the data page)
US Drought Monitor Map of CT
Current US Drought Conditions. Click to open source page.
The U.S. Drought Monitor is jointly produced by the National Drought Mitigation Center at the University of Nebraska-Lincoln, the United States Department of Agriculture, and the National Oceanic and Atmospheric Administration. Map courtesy of NDMC-UNL.
Link to Burlington Brook flow data
Above: recent flow at a typical CT stream.

Link to NWS graphic page
Check your forecast here.
Graphic courtesy NOAA NWS showing CT area watches and warnings if any.

July 14, 2016: Streamflow is still dropping to seriously low levels because 30-day rainfall is less than half of what we normally get over most of CT. Groundwater levels are low and dropping rapidly. These topics are discussed in more detail below. As described in our last Know Your Flow! update, the CT DPH issued the first Drought Advisory since 2010. They cite the low rainfall but emphasize that public water supplies are doing fine for now. The advisory, however, does not mention that between-storm streamflow continues to drop.

Streamflow. Click here for a display of all 70 USGS Connecticut area stream gages with graphs of their flow for the past 30 days compared to their daily average flows.  As of July 14, 11 of the 70 streams are flowing at rates lower than ANY of the daily averages at those sites. Forty-six of the 70 are flowing at rates less than 25% of all the average flows recorded at those sites for the date. This is actually an improvement from the beginning of the month due to recent rains. The streamflow map to the right from the USGS website displays a red dot to indicate flow below all records if that station has data for more than 30 years. Only four dots were in red status on July 14; the other seven record-low flows were at "newer" stations with records ranging from seven to 28 years of data. Most of the few dots indicating normal or above average flow are on streams where flow is controlled by releases from dams.

These stream gages normally show pulses of above-average flow when it rains, then below average between storms. Only a few of the records show Connecticut's streams rising above average at all during storms; most are barely reaching average and a few have not even come close to average. Dry conditions that cause flow to be below average more than it is above will affect stream life if these conditions continue for too long. For a review of the localized relationship between streamflow and precipitation, see below.

Groundwater:  The water level in streams and rivers between storms depends on the flow of water out of the ground into the stream channel. The higher the water table, the more water is available to keep streams flowing. During a drought, smaller upland streams dry up faster than the larger rivers (see the graph below). Groundwater levels recovered during the first three months of the year but have been dropping ever since.

Recent rains produced no improvement at the seven real-time monitoring wells run by the US Geological Survey (USGS). All seven report levels lower than 75% of their records for the date, including two that are lower than ANY records, and one that apparently went too low to measure. This continues a possible pattern of the last four years in which normal water levels in winter and spring have alternated with below-average in summer and fall. What is worrisome, however, is that the below-normal levels got worse each of those four years. Four years is not long enough to make any statistically valid conclusions about climate, however, and those station records only go back seven to 14 years. It was hoped that El Nino might have broken the pattern (if there is a pattern), but it ended in May. USGS manually measures other wells once a month or so, and a quick look at those records verified the possibility that the abnormally low yearly pattern seen in the real-time data may be getting worse.

Precipitation. According to the National Weather Service Advanced Hydrologic Prediction Service at this link (choose CT from the state drop-down list to see current data), most of CT has received less than half the normal precipitation in the last 30 days, with some areas less than 25% of normal. Recent rains have brought some relief to parts of the state, but not to areas out of the direct path of the storms. Even if we get the 3 inches of rain we would need to bring most of the state back to normal, if it fell as heavy precipitation, not all of it would soak in to keep our upland streams flowing between storms. 

The dire situation last year (see below) was caused not only by less total rainfall than normal over a long period of time but also by the intensity of the rain we did get. An occasional brief, powerful rainstorm does not do much to help groundwater levels rise. The rain falls faster than the ground can absorb, and thus much of it becomes stormwater runoff. In that situation, public water supply systems that depend on reservoirs are affected less than those with wells because the runoff is collected by the reservoir.

Rain? With some rain predicted, our streams may get some short-lived relief. The two-week forecast does offer a chance of maybe a couple inches of rain. Two inches of rain would not alleviate the entire state's 30-day rain deficit and certainly not our 60 day rain deficit of 4 to 6 inches.

The NWS Climate Prediction Center's July, and their 3-month prognostications give equal chances for normal or above average or below average precipitation. These forecasts said nearly the same thing for most of the dry period last year, yet we consistently got less than normal precipitation.

The amount of rainfall that has come during extreme precipitation events has risen faster in the northeastern United States than in any other region of the nation. Whenever there is a powerful storm, watch for flooding! Flash flooding can easily take people by surprise. Remember, if water is across the road, Turn Around, Don't Drown! See below for general flooding information.

Many public water supply companies asked for voluntary or mandatory restrictions on water use last year. The May 2016 monthly report from the CT Department of Public Health, however, reported no restrictions, with state reservoirs at an average 96% of their capacity, ranging from 71 to 100%.

Drought? The U.S. Drought Monitor week for July 12 labels 43% of Connecticut as "Moderate Drought" affecting 1,690,249 people with the rest of the state "Abnormally DryAs this graph shows, we have been labled like this pretty often over the last few years.


Dire situation last year.last year.

For a good analysis of last year's stream problems across the state, see this press release from Pomperaug River Watershed Coalition (PRWC). Here is a key quote:

The September and October low river flows demonstrate that rivers were not supporting the critical flows needed for a healthy river habitat. In fact, sections of the Weekeepeemee River had dry river beds and the Pomperaug River was flowing only at a rate of 15% of the critical flow requirement. DEEP officials confirmed that they would expect fish mortality to increase significantly during such conditions...

Click to enlarge
Photo from PRWC.

Meanwhile, parts of Coppermine Brook in Bristol were drawn down to rocks and dirt, as shown in the photo below taken Dec. 11 in Bristol. The sandy ditch in the foreground is the stream channel. Bristol Water Company and New Britain Water Company have eight registered diversions near Coppermine or its tributaries with a combined registered water withdrawal of 36.6 million gallons per day (source: CT DEEP). Company representatives report they do not withraw anywhere near that much water. Bristol Water says they stopped pumping from their well near this photo for a day but with no apparent effect on the stream. This is a perennial stream with a state Trout Management Area below where this picture was taken. Click on the photo for a full-screen version in a new tab.

Coppermine Brook, Bristol CT. Friday, Dec 11, 2015.
Coppermine Brook, Bristol CT, Friday, Dec. 11, 2015; photo by Tony Mitchell


This graph plots the rate of flow on Sept. 4 as a percentage of the median for each stream gage. For example, a dot at the 40% line means that stream that day was flowing at 40% of what could be considered normal for that date. The few rivers and streams flowing at or above 100% of their median rate are mostly those with flows managed by dam releases.

Some General Flood Information:

When floodwaters fill the part of the stream channel that is called a floodplain, the water may find that someone has built a building or two in the channel. The water then saturates and fills any leach fields, often flushing untreated sewage out into the flow.

The floodwaters also find these really nice holes in the ground called wells to flow down into. All kinds of interesting things can be delivered to the bottom of the well, such as the aforementioned sewage, and soil, bugs, leaves, pesticides such as weed killer and insect poison, even the dog droppings from the backyard.

Very important: Any well that was flooded should be pumped and flushed out thoroughly and the system sanitized or "shocked."

The Connecticut Department of Health website has a good guide called:

Flooding: Information for Homeowners About Private Wells, Sewage and Clean-Up

There are places in Connecticut where the storm drains and the sewage pipes are combined into one system. With high rainfall, many of these combined pipes are designed to overflow into rivers and streams so the wastewater treatment plants are not overwhelmed. You really do not want to be downstream when raw untreated human sewage is entering the water. The DEEP has a map of Combined Sewer Overflows that shows the six urban areas where these can occur. Zoom in to any of them to see exactly where the combined flow may enter streams and rivers. Not every rain event is enough to cause these overflows, but it's a good idea to avoid contact with the water downstream from them after significant rain.

Unless you are an expert paddler, do not attempt to canoe or kayak on floodwaters; there are usually one or two fatalities per year. Our Connecticut Water Trails website and the webpages of the many paddler groups in the state all have good safety procedures. Here is a good article.

Streamflow Graphs and Storms

Link to Aug 13, 2014 CT heavy rainfall effect on streamflow graphics courtesy USGS and NOAA.As the graphic to the right illustrates, where a storm moves across the state, the streams show flows that peak above their averages for this time of year but then quickly drop. The streams that maintain healthy flows between storms are those draining the parts of the state where there has been decent rainfall or those controlled by managed dams.

How quickly the flow drops after each rainstorm is unique for each stream, because it depends on how much water soaked in to increase the groundwater baseflow. In watersheds with lots of impervious roads, roofs, parking lots, patios, and compacted soil in lawns, a lot of the rain typically flows over the surface or through storm drains directly into the streams, leading to flooding problems far more often than in watersheds with mostly natural surfaces. Their streamflow then drops quickly after the storm ends, and the flow levels off far lower than in streams whose watersheds have more natural surfaces.

What IS Normal?

The National Oceanic and Admospheric Administration (NOAA) uses a rolling 30-year average of modern rainfall data to calculate its "normals." A discussion of the 1981 to 2010 precipitation calculations can be found at http://prism.oregonstate.edu/normals. To see Connecticut's average annual precipitation, go to http://prism.oregonstate.edu/gallery/view.php?state=CT_RI.

Recently there has been much discussion of what constitutes a "100-year-storm" or a "50-year storm." These traditional terms can be misleading unless you keep in mind they are an old-fashioned way of describing probablities. A "100-year" rainfall event means that in any year there is a 1% chance of that rate of rainfall.

Here is a map showing that in Connecticut we have a 1% chance of getting 7 to a little over 8 inches of rain in a 24-hour period, depending on where you are in the state. (Image source: http://precip.eas.cornell.edu/)

Comparing this to Table 7.2 (copy below) of the CT Stormwater Manual, we note that the design criteria for managing runoff possibly should be updated if we are building our landscape to control the flow from a 100-year-storm.


Drought pics

Photos by Joan Smith GOSA taken 9/20/2015 at The Merritt Family Forest in Groton. The stone slab bridge lies over Eccleston Brook, which had only a few puddles despite last week's downpour. The muddy bottom is also part of EB, further downstream. The photo with the two upright stone slabs is Cowslip Brook, a tributary to EB, and the wooden bridge traverses another small tributary to EB, flowing from a vernal pool. Used with permission.


More Links:

State of CT - Drought (Search)

State of CT Water Status website

USGS Connecticut DroughtWatch

Water Conservation tips

Water Conservation is not just for droughts; it is important because:

  • It saves money and energy

  • It insures the reliability of your water supply

  • It protects our natural resources

What Can I Do?

  • Set a voluntary water use reduction goal of 10% (whether served by public water systems or private wells)

  • Cut back on unnecessary water use, such as watering lawns or washing cars

  • Cooperate with your local water utility and follow their plans

Model Water Use Restriction Ordinance (PDF, 28KB)

Connecticut's Draft Drought Management Plan is being updated by the CT Water Planning Council Advisory Group Drought Plan Work Group.

 Websites for Some of the Water Companies in CT

AVON WATER CO http://www.avonct.gov/about-avon/pages/utilities-and-services  AVON
AQUARION WATER CO OF CT-CHIMNEY HEIGHTS http://www.aquarionwater.com/alerts.cfm?city=BETHEL BETHEL
AQUARION WATER CO OF CT-MAIN SYSTEM http://www.aquarion.com/alerts.cfm?city=Bridgeport BRIDGEPORT
BRISTOL WATER DEPARTMENT http://www.bristolwaterdept.org/ BRISTOL
AQUARION WATER CO OF CT-BROOK ACRES http://www.aquarionwater.com/alerts.cfm?city=BROOKFIELD BROOKFIELD
AQUARION WATER CO OF CT-BROOKFIELD SYS http://www.aquarionwater.com/alerts.cfm?city=BROOKFIELD BROOKFIELD
AQUARION WATER CO OF CT-OWSC BROOKWOOD http://www.aquarionwater.com/alerts.cfm?city=BROOKFIELD BROOKFIELD
AQUARION WATER CO OF CT-OWSC BUTTERNUT http://www.aquarionwater.com/alerts.cfm?city=BROOKFIELD BROOKFIELD
AQUARION WATER CO OF CT-CORNWALL SYSTEM http://www.aquarionwater.com/alerts.cfm?city=CORNWALL CORNWALL
CROMWELL FIRE DISTRICT WATER DEPARTMENT http://www.cromwellfd.org/Water_District.htm CROMWELL
AQUARION WATER CO OF CT-CEDAR HEIGHTS http://www.aquarionwater.com/alerts.cfm?city=DANBURY DANBURY
AQUARION WATER CO OF CT-HOLLANDALE EST. http://www.aquarionwater.com/alerts.cfm?city=DANBURY DANBURY
AQUARION WATER CO OF CT-KEN OAKS http://www.aquarionwater.com/alerts.cfm?city=DANBURY DANBURY
AQUARION WATER CO OF CT-PEARCE MANOR http://www.aquarionwater.com/alerts.cfm?city=DANBURY DANBURY
AQUARION WATER CO OF CT-ROLLING RIDGE http://www.aquarionwater.com/alerts.cfm?city=DANBURY DANBURY
AQUARION WATER CO OF CT-TLWC INDIAN SPRG http://www.aquarionwater.com/alerts.cfm?city=DANBURY DANBURY
DANBURY WATER DEPARTMENT http://www.ci.danbury.ct.us/content/21015/21087/21129/23057/default.aspx DANBURY
AQUARION WATER CO OF CT-NOROTON SYSTEM http://www.aquarion.com/alerts.cfm?city=Darien DARIEN
AQUARION WATER CO OF CT-EAST DERBY http://www.aquarionwater.com/alerts.cfm?city=DERBY DERBY
AQUARION WATER CO OF CT-EAST HAMPTON DIV http://www.aquarionwater.com/alerts.cfm?city=EAST HAMPTON EAST HAMPTON
EAST LYME WATER & SEWER COMMISSION http://eltownhall.com/water-sewer-utilities/ EAST LYME
HAZARDVILLE WATER COMPANY http://www.hazardvillewater.com/index.php ENFIELD
CTWC - UNIONVILLE SYSTEM https://www.ctwater.com/ FARMINGTON
AQUARION WATER CO OF CT-TLWC http://www.aquarionwater.com/alerts.cfm?city=GOSHEN GOSHEN
AQUARION WATER CO OF CT-GREENWICH SYSTEM http://www.aquarion.com/alerts.cfm?city=Greenwich GREENWICH
GROTON UTILITIES http://www.grotonutilities.com/ GROTON
METROPOLITAN DISTRICT COMMISSION http://www.themdc.com/customers/customer-advisories HARTFORD
AQUARION WATER CO OF CT-KENT SYSTEM http://www.aquarionwater.com/alerts.cfm?city=KENT KENT
AQUARION WATER CO OF CT-LEBANON DIVISION http://www.aquarionwater.com/alerts.cfm?city=LEBANON LEBANON
MASHANTUCKET PEQUOT TRIBAL NATION http://www.mptn-nsn.gov/tribaldepts.aspx LEDYARD
AQUARION WATER CO OF CT-CIRCLE DRIVE http://www.aquarionwater.com/alerts.cfm?city=LITCHFIELD LITCHFIELD
AQUARION WATER CO OF CT-LITCHFIELD SYS http://www.aquarionwater.com/alerts.cfm?city=LITCHFIELD LITCHFIELD
MANCHESTER WATER DEPARTMENT http://waterandsewer1.townofmanchester.org/index.cfm/water-supply-status/ MANCHESTER
UNIVERSITY OF CONNECTICUT - MAIN CAMPUS http://today.uconn.edu/2015/09/uconn-issues-water-supply-watch/ MANSFIELD
MERIDEN WATER DIVISION http://www.cityofmeriden.org/Content/Water_Division_Information/ MERIDEN
MIDDLETOWN WATER DEPARTMENT http://www.cityofmiddletown.com/content/117/123/185/default.aspx MIDDLETOWN
NEW BRITAIN WATER DEPARTMENT http://www.newbritainct.gov/index.php/city-services/water-department/general-information.html NEW BRITAIN
AQUARION WATER CO OF CT-NEW CANAAN SYS http://www.aquarionwater.com/alerts.cfm?city=NEW CANAAN NEW CANAAN
AQUARION WATER CO OF CT-BALL POND SYS http://www.aquarionwater.com/alerts.cfm?city=NEW FAIRFIELD NEW FAIRFIELD
AQUARION WATER CO OF CT-OAKWOOD ACRES http://www.aquarionwater.com/alerts.cfm?city=NEW FAIRFIELD NEW FAIRFIELD
AQUARION WATER CO OF CT-OWSC BIRCHES http://www.aquarionwater.com/alerts.cfm?city=NEW FAIRFIELD NEW FAIRFIELD
REGIONAL WATER AUTHORITY http://www.rwater.com/stewardship/how-much-water-do-we-have/ NEW HAVEN
NEW LONDON DEPT. OF PUBLIC UTILITIES http://ci.new-london.ct.us/content/7429/7431/7459/default.aspx NEW LONDON
AQUARION WATER CO OF CT-CARMEN HILL http://www.aquarionwater.com/alerts.cfm?city=NEW MILFORD NEW MILFORD
AQUARION WATER CO OF CT-DEAN HEIGHTS SYS http://www.aquarionwater.com/alerts.cfm?city=NEW MILFORD NEW MILFORD
AQUARION WATER CO OF CT-FOREST HILLS SYS http://www.aquarionwater.com/alerts.cfm?city=NEW MILFORD NEW MILFORD
AQUARION WATER CO OF CT-INDIAN RIDGE http://www.aquarionwater.com/alerts.cfm?city=NEW MILFORD NEW MILFORD
AQUARION WATER CO OF CT-MEADOWBROOK http://www.aquarionwater.com/alerts.cfm?city=NEW MILFORD NEW MILFORD
AQUARION WATER CO OF CT-NEW MILFORD http://www.aquarionwater.com/alerts.cfm?city=NEW MILFORD NEW MILFORD
AQUARION WATER CO OF CT-PARK GLEN SYSTEM http://www.aquarionwater.com/alerts.cfm?city=NEW MILFORD NEW MILFORD
AQUARION WATER CO OF CT-PLEASANT VIEW http://www.aquarionwater.com/alerts.cfm?city=NEW MILFORD NEW MILFORD
AQUARION WATER CO OF CT-TWIN OAKS SYSTEM http://www.aquarionwater.com/alerts.cfm?city=NEW MILFORD NEW MILFORD
AQUARION WATER CO OF CT-CHESTNUT TREE http://www.aquarionwater.com/alerts.cfm?city=NEWTOWN NEWTOWN
AQUARION WATER CO OF CT-NEWTOWN SYSTEM http://www.aquarionwater.com/alerts.cfm?city=NEWTOWN NEWTOWN
AQUARION WATER CO OF CT-OWSC http://www.aquarionwater.com/alerts.cfm?city=NEWTOWN NEWTOWN
AQUARION WATER CO OF CT-NORFOLK SYSTEM http://www.aquarionwater.com/alerts.cfm?city=NORFOLK NORFOLK
AQUARION WATER CO OF CT-NORTH CANAAN SYS http://www.aquarionwater.com/alerts.cfm?city=NORTH CANAAN NORTH CANAAN
NORWALK FIRST TAXING DISTRICT http://www.firstdistrictwater.org/en_US/news/5/26/No-Alert NORWALK
NORWICH PUBLIC UTILITIES http://norwichpublicutilities.com/for-my-business/services-business/80-water#Water NORWICH
AQUARION WATER CO OF CT-HAWKSTONE SYSTEM http://www.aquarionwater.com/alerts.cfm?city=OXFORD OXFORD
VALLEY WATER SYSTEMS, INC. http://www.valleywatersystems.com/ PLAINVILLE
AQUARION WATER CO OF CT-SALISBURY SYS http://www.aquarionwater.com/alerts.cfm?city=SALISBURY SALISBURY
AQUARION WATER CO OF CT-VALLEY SYSTEM http://www.aquarion.com/alerts.cfm?city=Seymour SEYMOUR
AQUARION WATER CO OF CT-TIMBER TRAILS http://www.aquarionwater.com/alerts.cfm?city=SHERMAN SHERMAN
AQUARION WATER CO OF CT-SIMSBURY SYSTEM http://www.aquarion.com/alerts.cfm?city=Simsbury SIMSBURY
AQUARION WATER CO OF CT-LAKESIDE SYSTEM http://www.aquarionwater.com/alerts.cfm?city=SOUTHBURY SOUTHBURY
SOUTHINGTON WATER DEPARTMENT http://www.southington.org/content/17216/17776/default.aspx SOUTHINGTON
AQUARION WATER CO OF CT-STAMFORD http://www.aquarion.com/alerts.cfm?city=Stamford STAMFORD
AQUARION WATER CO OF CT-MYSTIC http://www.aquarion.com/alerts.cfm?city=Mystic STONINGTON
TORRINGTON WATER COMPANY http://www.torringtonwater.com/index.html TORRINGTON
WALLINGFORD WATER DEPARTMENT http://www.town.wallingford.ct.us/Content/Water_and_Sewer_Divisions.asp WALLINGFORD
AQUARION WATER CO OF CT-JUDEA DEPOT http://www.aquarionwater.com/alerts.cfm?city=WASHINGTON WASHINGTON
AQUARION WATER CO OF CT-JUDEA MAIN http://www.aquarionwater.com/alerts.cfm?city=WASHINGTON WASHINGTON
AQUARION WATER CO OF CT-QUARRY RIDGE http://www.aquarionwater.com/alerts.cfm?city=WASHINGTON WASHINGTON
WATERBURY WATER DEPARTMENT http://www.waterburyct.org/water WATERBURY
WATERFORD WPCA http://www.waterfordct.org/utilities WATERFORD
WINDHAM WATER WORKS http://www.windhamct.com/townhall_dept_waterworks.htm WINDHAM
AQUARION WATER CO OF CT-TLWC CLEARVIEW http://www.aquarionwater.com/alerts.cfm?city=WOLCOTT WOLCOTT
AQUARION WATER CO OF CT-TLWC WOODRICH http://www.aquarionwater.com/alerts.cfm?city=WOLCOTT WOLCOTT
AQUARION WATER CO OF CT-WOODBURY SYSTEM http://www.aquarionwater.com/alerts.cfm?city=WOODBURY WOODBURY

Rivers Alliance of Connecticut
PO Box 1797, 7 West Street 3rd Floor, Litchfield, CT 06759-1797
rivers@riversalliance.org, www.riversalliance.org