Low flows continue on area rivers

An inch of rain overnight Sunday, Aug. 21, brought the Souhegan River back up over the Protected Criti­cal Instream Flow that would require water users and towns along the river to curtail outside watering, but the low flows are still the topic of concern.

Flow in the upper section of the Souhegan was only 25 percent of its historic ex­pected flow. This is a slight improvement from two weeks ago when the Souhe­gan Watershed Association water quality monitoring last took place, but unless more rain continues, the river will shortly return to critical flows.

The Merrimack River is ponded by the dam in Low­ell, Mass., up through Nash­ua and so the level is less evident here, but the flows measured in Manchester are down about 25 percent. At the time of the tests the flow should have been 1400 cubic feet per second, but it was measured at 1090 cfs.

What this means for the E. coli tests is that there is less water to dilute pollu­tion. Ironically heavy rains raise the E. coli levels tem­porarily – about three days – as pollution from storm drains and river banks gets washed into the rivers. This is especially true after a dry period preceding the rain.

This week E. coli lev­els reflect that. Both the Souhegan and Merrimack Rivers showed high E. coli counts – but for dif­ferent reasons. The Mer­rimack is a large river that can dilute pollution that would overwhelm the much smaller Souhegan. Seldom do E. coli counts rise to dangerous levels on the Merrimack, but this week they did. The heavy rain caused the Manches­ter sewage treatment plant to release raw sewage di­rectly into the river. E. coli counts rose above the 406 dangerous level all the way to Merrimack. But as an indication of the power of dilution, the E. coli count was back down to accept­able levels by the time the river reached Nashua. The E. coli level at the Greeley Park boat ramp measured only 43.

The much smaller Souhegan River did not have the very high num­bers that showed up on the Merrimack, but the entire river was above the 88 level that indicates clean water. All of the swimming holes tested above the 88 level but most were below 126, which is acceptable swim­ming for healthy adults. Weston Park at Turkey Hill Bridge in Merrimack was slightly higher at 147, too high for swimming. The Amherst Canoeport at Bos­ton Post Road was too high at 206. All other swimming holes were OK.

E. coli monitoring is for human use of the riv­ers only and a good indi­cator of pollution levels, but SWA also monitors for dissolved oxygen in both rivers. DO levels give the best general indication of the health of the river it­self. And monitors found generally good levels of DO again this week. This has been true all season. The rivers are clean for fish and other river crea­tures and for the environ­ment. More information about DO and the actual readings for each site are listed at www.souhegan river.org.

This is the final test for this season. We hope to continue next June to be­gin our 21st testing sea­son. Tests are all done by Souhegan Watershed Asso­ciation volunteers who col­lect samples and data from 30 specific sites on both riv­ers and transport the sam­ples to wastewater treat­ment plants in Manchester, Greenville, Milford, Nash­ua and Merrimack, where they’re picked up, moved around, and processed by certified lab technicians at the wastewater treatment plants.

– Submitted by Souhegan Watershed Association