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Generally, streamflow across the state has been trending downward since the major rain event of December 20-22 dropped several inches of rain across the state. Smaller storms since then arrived often enough to keep streamflow above normal for the time of year. As of Jan 14, 5 of 61 operating USGS stream gages in Connecticut were reporting very high flows for the date. Another 27 were reporting high flows. The remaining 29 gages were reporting near-normal flows for the date. Two gages, Ridgefield Brook at Shields Lane near Ridgefield and Indian River near Clinton, were the only ones that have dropped below average for the date. With no precipitation predicted for a few days, these gages may soon report low streamflow for the first time since July. One stream gage, on the Farmington River, is out of operation and with the federal government shutdown, it is not known when it will be repaired.
We define high flow as at or over the stream's 75th percentile for that date, very high at 90th or higher, from the data file at https://waterwatch.usgs.gov/webservices/realtime?region=ct&format=xml when rivers are near their low points between storms. Low streamflow is below the 25th percentile.
Why do we count? The flow between storms is an indicator of long-term stream conditions. Although expansion of a river or stream channel onto its floodplain is a normal, natural occurrence, human interference can cause higher than normal and more frequent flooding. The higher the water level remaining in streams and rivers before a storm, the more likely there will be dangerous conditions, streambed scouring, and other detrimental effects of high water.
When water levels are low, portions of the streambed become too dry to support the aquatic life that usually colonizes those areas. Groundwater seeping from the stream banks can help organisms survive for short times; therefore, well measurements can also be used to identify areas where aquatic life might be in jeopardy.
In Connecticut, the USGS has 10 real-time groundwater monitoring wells. All of them show large rises in the water table in November to record-setting, well-above-normal levels for the time of year. Since then, the water level in these wells has been more or less steady, showing the expected rises after storms and drops between them.
Because the normal pattern for groundwater is to increase during this time, the calculated percent above normal has decreased. As of Jan 14, 4 of the 8 wells with multiple-year records were still reporting record-high water levels for the date; another 2 were still reporting above-normal levels. 2 of the 8 wells were near-normal though still above average levels for the date.
The USGS Groundwater Watch website displays data from 60 other wells that are usually measured once a month, comparing the most recent measurements to each well's measurements taken in that month in previous years. As of Jan 15, only 29 of them have measurements less than a month old, probably due to the federal government shutdown.
Of 29 wells measurements taken on Dec 21, only 8 were near normal for the end of December. 19 were at above-normal or much-above-normal levels, 2 others were breaking high-level records for December.
Groundwater levels influence streamflow. 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. High water tables keep streamflow from dropping very far or very fast between storms, so when the next storm hits, the runoff pushes streams to higher levels with more flooding.
During a drought, smaller upland streams dry up faster than the larger rivers (click here for details from a previous Know Your Flow! webpage). 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 contrast, public water supply systems that depend on reservoirs benefit from heavy rains because the reservoirs collect the runoff. The runoff, however, can wash pollutants into the reservoirs, lowering water quality.
Normal January precipitation across Connecticut ranges from 3 to 5 inches for the month. As of Jan 14, we have received about half of that, so we are now at an average amount for the month. Go to the National Weather Service (NWS) Advanced Hydrologic Prediction Service at this link for updated, detailed maps and data about precipitation amounts for Connecticut at various time frames.
Click here for a prediction of total precipitation for the next 15 days.
For technical information about past broad-scale weather patterns, see NOAA's National Centers for Environmental Information State of the Climate Synoptic Discussions.
Your water utility and town are the best sources of information on the status of your water supply. A few systems post their current capacities regularly on their websites. Aquarion maintains on its website a weekly updated water usage report for their systems in southwest CT. The report includes water demand graphs, system transfers, system capacities, days usable storage remaining, and precipitation. As of Jan 8, all their systems were at 99%-100%, well above where each system usually is at this time year based on a 20-year average. As of Jan 1, MDC reservoirs were at "100% of capacity with over 39 billion gallons in storage representing 664 days of supply assuming typical water use and no precipitation."
The most recent CT Department of Public Health's Monthly Reservoir Status Summary was for Sep 26. At a Water Planning Council meeting, a DPH representative reported that a new, more comprehensive and timely report system should be online in 2019.