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Connecticut Streamflow Overview

Connecticut Streamflow Overview

Know The Flow!

Friday Sep 5, 2014 Summary: Its dry out there! Groundwater levels are plummeting. All the USGS measuring stations in CT are recording well levels lower than average for this time of year. Click here to see the graphs. Chances are that the thunderstorms predicted for tomorrow Saturday Sep 6 will not change the groundwater levels very much because soil has a maximum rate it can absorb water. If more rain falls in any given time than can be absorbed, the extra runs off the land and does not contribute to groundwater.

The streamflow state map at http://waterdata.usgs.gov/ct/nwis/rt is starting to show the red symbols for flow rates under the 10th percentile which means less than 20% of the average for this time of year. The streams with green symbols that represents flows within 25% of average are all actually lower than the numerical mean.

According to The Advanced Hydrological Prediction Service of the National Weather Service, Connecticut rainfall during the last 30 days (as of Sep 5 ) was average for this time of year over the whole state, but there are significant differences within the state. The northwest and north central parts of the state have received above average rainfall but the very southwest corner has seen less than half the rainfal it notmally gets at this time of year. The rest of the state is at about average for this time of year. Keep in mind however that the rain has come mostly as high intensity events that do not contribute to groundwater much more than a normal rainfall would.  Connecticut rainfall during the last 60 days shows most of the state below or well below average with only the northwest corner at or above average. It is the long term rainfall totals that control groundwater levels that in turn keep streams flowing between storms. The USDA Drought Monitor for Tue Sep 2 reports almost 49% of the state Abnormally Dry, the same as the previous week.

Link to Aug 13, 2014 CT heavy rainfall effect on streamflow graphics courtesy USGS and NOAA.The US Geological Service Streamflow Map of Connecticut (on Fri Sep 5) shows that only streams in the northwest third of the state at their average flows for this time of year, but the individual hydrographs even for them show flows below the numerical mean.

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 only streams that are maintaining healthy flows between storms are those draining the northwest part of the state where they have had decent rainfall, or on streams 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. Watersheds with lots of impervious roads, roofs, parking lot, patios, and compacted soil in lawns typically cause a lot of the rain to flow over the surface or through storm drains directly into the streams, leading to flooding problems far more often than natural surfaced watersheds. Their streamflow then drops quickly after the storm ends and the flow levels off far lower than streams with more natural surfaces in their waterheds.

Even though its dry now, Watch for Flooding when it rains!
Flash flooding can easily take people by surprise under these conditions because powerful thunderstorms up the watershed can cause rapid stream rises even if it did not rain in a particular location.  Remember if water is across the road, Turn Around Don't Drown! Only crazy people attempt to canoe or kayak on floodwaters, but apparently there are enough of them to cause 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. 

When floodwaters return to use that 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 back yard. It is very important that any well that was flooded be pumped and flushed out thoroughly and the system sanitized or "shocked".  The Connecticut State Department of Health website has a good guide called: Flooding: Information for Homeowners About Private Wells, Sewage and Clean-Up

Also, 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 its a good idea to avoid contact with the water downstream from them after significant rain.

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

The Drought Work Group of the Connecticut Water Planning Council is developing an updated Connecticut Drought Preparedness and Response Plan DRAFT. The outdated 2009 State of CT Drought Preparedness and Response Plann authorizes the state to issue a Drought Advisory if the majority of the following criteria are met:

Criteria to Declare Drought Advisory
Precipitation: Two months cumulative below 65% of normal
CT State Water Status
Ground Water: Three consecutive months below normal,
USGS Groundwater
Streamflow: Two out of three months below normal,
Burlington Brook Streamflow
Reservoirs: Average levels less than 80% of normal..
CT State Water Status
Palmer Drought Severity Index::
 -2.0 to -2.99 (moderate drought)
Palmer Drought Index
Crop Moisture Index: range of
 -1.0 to –1.99 (Abnormally Dry)
Daily(ish) Forest Fire Danger Report
Click on any graphic below for more informationion
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High Flow    Low Flow
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Not
Ranked
CT Current Streamflow. Click to go to source page.
Streamflow in CT (click to go to the data page)
Current US Drought Conditions. Click to open source page.
Link to US Drought Monitor
Link to Burlington Brook flow data
 

 

More Links:

State of CT - Drought (Search)

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)

Rivers Alliance of Connecticut
PO Box 1797
7 West Street, 3rd Floor
Litchfield, CT 06759
860-361-9349
rivers@riversalliance.org
www.riversalliance.org