In September as shown on the Bridgewater USGS River Flow Gage, the drought in our watershed continued despite two significant short storms of moderate intensity. On 9/6 three days before we sampled, the Taunton River flow was only 54 cubic feet per second (cfs) a very low flow for this river comparable to any drought low flow we have seen in the last two years. On 9/7 a storm brought flow up to 210 cfs but because the river has not recovered from 2024 drought conditions and low water table the river flow quickly dropped to 119 cfs by 9/9 the morning we sampled. After brief intense storms the river flow quickly rises then quickly falls. This pattern is the classic signature of a river and watershed in drought condition.
As discussed last month the weather pattern we are seeing is very close to that predicted by global warming models for our area. These models predict late winter early spring heavy rain and potential flooding followed by drought. On May 24, 2025 river flow was 2,260 cfs with brief concerns of flooding however because the watershed had not recovered from drought in 2024 river flow dropped quickly. Global warming induces hot dry summers punctuated by brief intense rainstorms which can cause short term local flooding and wind damage. But as we see from the record these brief summer rainstorms don’t replenish watershed groundwater and base river flows which drop quickly after the storms. These summer storms do deliver stormwater runoff pollution to rivers and streams. As the rest of the U.S. and countries of the world are seeing extreme weather is the calling card of global warming.
The results for September as a consequence of low river flow show somewhat higher levels of nitrogen likely due to less river dilution of wastewater treatment plant (WWTP) effluent and the fact that many lawn companies and homeowners are applying fall fertilizer applications not only to lawns but roadways and sidewalks. The rain before we sampled washes this “lawn” nitrogen into the river.
In most locations Total Phosphorus was below our water quality target. Total Phosphorus was high in the Town River because Bridgewater has not completed the phosphorus removal upgrade required by 5/01/2027 in their Clean Water Act (CWA) permit. Phosphorus was no longer high in the Segregansett River possibly due to the Segregansett Golf Course not applying starter fertilizer containing phosphorus. It was elevated in Berkley as well, possibly because the Taunton WWTP is not required to remove phosphorus because it discharges to tidal brackish water where nitrogen is considered the nutrient of most concern.
Like the previous four months, the low river flows and warm temperatures resulted in bacteria (enterococci) water quality standards violations in almost all sampling locations. The magnitude of violations was higher in many locations because we were sampling two days after a rainstorm. Even though we had missed the first flush of the highest concentration of stormwater pollutants by a couple of days the bacteria violations were significant.
Typically the biggest water quality problem in our watershed is bacteria levels with almost all monitoring stations exceeding the enterococci water quality criterion of 35 colony forming units (CFU) by large amounts after rainstorms. This is a result of lack of stormwater treatment by green infrastructure such as infiltration basins, infiltration trenches, rain gardens, tree filters, etc. in the watershed. Stormwater infiltration even if there is only physical space for an undersized unit that captures and treats the first flush is effective for bacteria and phosphorus control.
Because of TRWA documented water quality standards violations caused by stormwater throughout the Taunton River watershed TRWA believes EPA should use its “residual designation authority” to regulate large non-regulated commercial stormwater sources in our watershed. The Clean Water Act (CWA) recognizes that other stormwater sources may need to be regulated on a case-by-case or category-by-category basis based on additional information or localized conditions. The authority to regulate other sources based on the localized adverse impact of stormwater on water quality through CWA permits is commonly referred to as the “Residual Designation” authority.
Our next sampling day is Tuesday, October 14th. We will be watching to see if river flow continues low. If there is a brief rainstorm just prior to our sampling, whether it delivers enough stormwater pollution to cause high magnitude bacteria water quality standards violations and how river temperature affects our bacteria results.