Connecticut Streamflow and Groundwater Overview
Know Your Flow!
CT Conditions At A Glance(Click on any graphic below for more information)
in CT Now
(click map to go to the data page)
High Flow Low Flow Not Ranked
US Drought Monitor Map of CT
(click map for details)
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.
Map of Below Normal 28-Day Average
Recent Flow At a Typical CT Stream
(click graph for details)
(click graph to see more well data)
Check your forecast here
(click map to go to state weather page)
Graphic courtesy NOAA NWS showing CT area watches and warnings if any.
Feb 24, 2017 Update
Summary (details below)
The area of Connecticut rated Extreme Drought by the U.S. Drought Monitor remains at 28%, after a small decrease three weeks ago. 48% of the state is rated Severe, and the rest is rated Moderate. By percent of area, CT continues to be the most drought-afflicted state of all 50.
Overall streamflow is closer to normal than we have seen
since last Winter, but once the snow has completely melted flow will drop again
unless we get decent rainfall. The improvement in groundwater levels
has slowed, and remains low for half of the
worst drought since the
historic drought of the 1960s continues.
Interagency Drought Workgroup (IDW)
met Jan. 20 and decided not to recommend any changes to the state's drought alert level. The Drought Watch
continues for six CT counties; Drought Advisory continues for the eastern two
counties. The state is still requesting all residents to reduce their water use by
Most water utilities have ended conservation measures they had previously called for because their reservoir levels now show much improvement (for details, see Utility Alerts below).
Due to the rapid snowmelt, flow in all streams has increased over the past week. As a result, the number of CT rivers and streams measured by the US Geological Service (USGS) that are experiencing low baseflows has improved to just 11%. An alphabetical list of low-flow rivers is below. The graphs for most river and stream gages are showing a normal pattern of about equal areas above-average flow when it rains (or there are days with rapid snowmelt), then below-average between storms and days without snowmelt. See Streamflow Graphs and Storms below for more explanation.
Due to the ongoing drought conditions, The Department of Energy and Environmental Protection (DEEP) issued a Public Notice that it "...suspends the minimum stream flow standards ... commonly known as the 'spring freshet' release standard, for the period of February 15, 2017 to March 15, 2017.... Questions regarding this action may be directed to Doug Hoskins, ... 860-424-4192, firstname.lastname@example.org."
Dry conditions that cause flow to be below
average more often than it is above average is affecting stream
life throughout the state. Fishermen have reported long stretches
of rivers with no catch at all. Whatever dormant life is left on
our stream bottoms will be lost if flow remains too low to prevent
the stream from freezing solid if temperatures return to normal for this time
of year. This is different from the common winter fish kills explained in fact
sheets from CT DEEP.
Your water utility and town web pages are
the best sources of information on water use restrictions that
apply specifically to you. The Department of Public Health's (DPH) Reservoir
Data monthly web page dated Feb 6 stated that capacity was
at 87% of normal, the percentage reported on their
Monthly Reservoir Status Summary for January. (Note that "normal" for
January is 91% of
capacity.) The 87%
of normal is based on reports from 34 large water systems that use
reservoirs. That percentage means those reservoirs averaged
80% of capacity. Most of those water utility companies had
issued water use restrictions or asked for voluntary conservation. The DPH also has a
separate list of
Public Water Systems with water use restrictions, last
updated Dec. 12, 2016.
Aquarion maintains on its website a weekly updated water usage report that includes customer usage trends, system transfers, system capacities, days usable storage remaining, and precipitation. Their graphs and charts indicate conditions are near or even above their trigger levels for water usage alerts.
According to the Greenwich Times, Greenwich, Stamford, Darien and New Canaan are working with Aquarion on a water-demand study that could be completed next month. They are examining the overuse or water that, combined with years of below-average rain and snow, has caused a statewide drought. The study could result in permanent water conservation guidlines.
The water table normally reaches its highest levels from this time of year until late Spring. Over the last few weeks the water in most wells has either slowed its steady rise or has leveled off. Day to day, groundwater has been moving up with rainfall and snowmelt, but then it drops again. If this year's plateau has been reached, it does not bode well for our rivers and streams if drought conditions intensify again.
On Feb 24, two the six real-time monitoring wells run by the USGS with multi-year records were reporting a water table lower than any daily averages for the date for those wells. One other, though not setting records, were lower than 75% of its averages for the date. The other three wells are near or above average.
Until the past few weeks, all eight live-data stations were showing the water table recovering steadily from the their lowest levels in September. Until November, more stations were breaking low-water-level records than those that were merely very low.
The USGS Connecticut office this year added live-data access to two additional wells, in Clinton and Salisbury. The live data displayed by these goes back to August of last year, but comparisons to their monthly measurements of previous years can be made using the USGS's Groundwater Watch website. For example, the February 14 measurements from the Clinton and Salisbury wells were close to normal for their February measurements going back decades. The most recent measurements at almost half the wells on the Groundwater Watch website were near or above normal, 28% were labeled below normal, 23% were much below normal.
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 (details below). 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 reservoirs. How much groundwater is contributed by snow depends on several factors including slope, rate of snow melt, and whether the ground beneath the snow is frozen or saturated.
There has been an apparent pattern for the last five years in which normal groundwater levels in winter and spring have alternated with well-below-average in summer and fall. Click the graph to the right for a larger version in a new tab of a modified USGS graph. What is most worrisome, however, is that the below-normal levels got worse in each of those years. Five 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. Click here to see all the USGS graphs for their real-time groundwater measurements that compare levels from the last four years to the median level for each day of the year (lots of data, so it takes a long time to load). USGS manually measures other wells once a month or so, and a quick look at those records verified the possibility that this pattern may apply to all our groundwater.
(See also climate news: Climate Change Threat to Both the Natural World and to Human Civilization)
Why is Connecticut still in Drought Watch and Advisory status? Here is a summary of what was discussed at the Interagency Drought Workgroup (IDW) on Jan. 20:
While the Interagency Drought Workgroup acknowledged that conditions have stopped deteriorating and have improved in some areas, the improvement was not sufficient to lift the posted Drought Watch and Drought Advisory that were issued in the fall. Of significant concern is the relatively mild winter weather and lack of snow pack, meaning that continued recharge and recovery in the spring is not guaranteed unless Connecticut remains in a pattern of active stormy weather. The Department of Public Health noted that many reservoirs are still struggling to recharge and it is entirely possible that some reservoirs will not fully recharge by spring. As of January 20, reservoir capacity statewide was at 73%, well below the normal 92% for that time of year. Stream flows had recovered nicely across the state through the month of January, except where water companies were holding back large amounts of water to refill flow-of-the-river reservoirs. For example, MDC continues to withhold large amounts of water from the West Branch Farmington and East Branch Farmington, therefore keeping stream flows low in the Farmington River. Groundwater wells were showing improvement statewide, but many wells were still trending at or near record lows for the time of year. The Interagency Drought Workgroup also considered observed precipitation, the Palmer Drought/Crop Moisture indices, and fire danger, all of which are available at www.ct.gov/waterstatus. The State will remain under a Drought Watch, with the exception of New London and Windham Counties that are under a Drought Advisory, until the workgroup meets again in February to reassess conditions. State agencies continue to implement drought management and mitigation actions as specified in the Connecticut Drought Preparedness and Response Plan.
Below-normal precipitation over the two weeks has brought our thirty-day average to under half of what we would normally get at this time of year. Near-average precipitation had been gradually improving long-term streamflow and groundwater levels. According to the National Weather Service Advanced Hydrologic Prediction Service, the Jan 22-23 rain nor'easter brought 30-day precipitation to near average for most of Connecticut. Precipitation was then below normal until the frequent snowstorms Feb 7-12 bounced us back to normal 30-day amounts. Periods of unusually heavy precipitation like this do not compensate for unusually dry weather even if they average out to normal because heavy rain does not all soak in to recharge groundwater. If snow melts slowly enough that most of the water infiltrates the soil, it can help to improve long-term drought conditions. The rapid melting recently with unseasonably warm temperatures is not replenishing groundwater very much. Go to this link for detailed maps and data.
For most of 2016, storm tracks brought precipitation out to sea or north of us because a persistent high-pressure system called a blocking pattern was diverting weather fronts and storms. It was only when that blocking pattern moved away for short periods that some weather systems came over Connecticut, creating temporary returns to more normal rainfall. That normal precipitation did not end the drought due to the serious long-term rain deficit, but it kept it from getting worse for a while. Streamflow between storms continued to drop to low levels, however.
This is the same bad situation that we had in 2015-2016 (see below), 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. Not all drought conditions went away last winter. As our climate changes, heavy precipitation events are becoming more frequent. Heavy rain does not recharge groundwater aquifers as much as the same amount of rain over longer periods would.
Rain? The National Weather Service's
one-week forecasts and their
long-range (16-day) computer models
are predicting below normal precipitation. Long-range forecasts are of course highly suspect. The series of
snowstorms that delivered decent snowfall Feb 8-12 had been predicted 2 weeks
earlier to track out to sea.
Each month, the NWS Climate Prediction Center issues analyses of global atmospheric conditions that could influence general temperature and precipitation patterns. Their Feb 16 analysis for trends through May 2017 show equal chances for above-normal, normal, and below-normal precipitation. Above-normal temperatures are a little more likely than normal temperatures. This is pretty much the same four-month forecast we had seen for the past year, but actual precipitation was much lower than normal. The NWS Climate Center's prognostications for the summer, however, give a 40% chance for above-normal rainfall, a 33% chance of normal, and a 27% chance for below-normal. This prediction has not been seen in several years. Summer temperatures are also predicted to be above normal.
Melting snow continues to temporarily bring up flow rates. On February 24, only 7 of the 62 Connecticut rivers and streams measured by the USGS, (listed below) were experiencing low flows*, the same number as last week. This is a significant improvement from February 14 when there were 23, and from February 6 when there were 34 low-flow streams. In January there were 28 on the 23rd, on the 17th there were 27, and on January 10 there were 35. During most of 2016, there usually 50 to 60 low-flow streams, numbers last seen on December 23 when there were 53.
On Feb 24 only one stream gage was reporting flow lower than any record for the date, on the Saugatuck River (in bold red below). There were two of them each of the last two weeks. This is an improvement since Feb 6 when there were seven record breakers, nine record breakers on Jan. 23, five on Jan. 19 and Jan. 10. The number of record breakers were even higher last year, for example there were fifteen on Dec. 23. To see the status of any them right now, click the station's URL.
|Station Name||Station Website|
|FIVEMILE RIVER NEAR NEW CANAAN, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01209761|
|HOUSATONIC RIVER AT STEVENSON, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01205500|
|LATIMER BROOK NR I-95N EXIT 75 NR FLANDERS, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=011277905|
|MILL RIVER NEAR FAIRFIELD, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01208925|
|RIPPOWAM RIVER AT STAMFORD, CT.||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01209901|
|SAUGATUCK R BELOW SAUGATUCK RES NR LYONS PLAIN, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01209005|
|WEST BRANCH FARMINGTON RIVER AT RIVERTON, CT||https://waterdata.usgs.gov/ct/nwis/uv?site_no=01186000|
*We are defining low flow as below the 25th percentile for that stream, OR below 25% of the mean OR below 25% of the median flow for that stream for the date. Data source: https://waterwatch.usgs.gov/webservices/realtime?region=ct&format=xml on Friday Feb. 24, 2017. Click here for a list of all CT stream gages comparing their flow right now to their mean and median flows for today's date.
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.
The U.S. Drought Monitor publishes a weekly analysis of drought conditions across the entire nation based on a variety of types of data that include streamflow. The report comes out every Thursday based on data from that Tuesday. Since the Drought Monitor began in 2000, the only time any part of Connecticut was as dry as it is now was 2002, when around 16% of the state was in the Extreme category for three weeks. This means this is the worst drought so far this century. The U.S. Drought Monitor is produced by the National Drought Mitigation Center, which is also on Facebook.
For several weeks, the 76% of Connecticut rated Extreme and Severe has given us the dubious distinction of the highest percentage of area under those rankings of all 50 states . We were sixth in actual square miles on Jan 31. The next most drought-afflicted state on Feb 7 was Oklahoma with 31% of their area Severe and Extreme. The Drought Monitor's narrative for the northeast for Jan 31 explained: "In western Connecticut and southwestern Massachusetts, minor reductions in areas of Severe Drought (D2) and Extreme Drought (D3) were made in response to short-term improvements in streamflow conditions and soil moisture. The longer-term impacts to groundwater, however, remain across portions of both Connecticut and Massachusetts."
As the below graph shows, Connecticut has been labeled Abnormally Dry, Moderate Drought, or worse pretty often over the last few years. This graph was made before any of the state was rated as Extreme.
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...
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, 2015, 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; photo by Tony Mitchell
Some archived Know Your Flow pages
http://www.riversalliance.org/drought/droughtarchive.cfm?filename=droughtbefore20150925.htm http://www.riversalliance.org/drought/droughtarchive/droughtbefore20150903.htm http://www.riversalliance.org/drought/droughtarchive/droughtbefore20160316.htm