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The Sheepscot River Turbidity Pilot Study, - page 6 / 12

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West Branch as observed at the Howe Road.  There are additional sources of sediment in the lower river between North Whitefield and Alna.  This time, the West Branch is relatively clear at Weeks Mills.  Meadow Brook was not sampled this time, but it may be the source of the relatively mild turbidity observed at Weeks Mills.  Choat Brook is again mildly turbid but probably not as much as the West Branch at this point (Windsor Station was not sampled this time either).  The lower West Branch between Weeks Mills and the Howe Road has accumulated a lot of additional sediment.  It is clear that the spatial patterns in turbidity, and by extension the sediment sources, are not stable throughout the year.  For instance, in May, the mainstem was muddier than the West Branch.  In October, the West Branch was much worse than the mainstem.

Table 2.  Total Suspended Solids (TSS) and Turbidity for SVCA samples of October 12-13, 2006.  Sample sites are listed from upper to lower river reaches on the West Branch and mainstem of the Sheepscot River.

W Branch

TSS

Turb

Mainstem

TSS

Turb

mg/L

NTU

mg/L

NTU

Palermo

4.2

1.8

Hatchery

3.2

1.3

Meadow Br

Coopers Mills

3

2.7

Weeks Mills

5

5.3

No Whitefield

12

15

Choat Brook

8.6

3.9

Alna

43

32

Windsor Station

Howe Road

50

38

In June, DEP did some sampling before, during, and after a high flow event.  The river gauge at North Whitefield went from 734 cfs to 1,430 cfs over a period of four days.  The storm of June 7 built onto the flood stage from a previous storm of June 3-4 (representing 3.25 inches of rain over two days).  The flood peak was the second highest flow of 2006 for the Sheepscot River (the highest flow of the year was 1,800 cfs on October 29).  The first samples were taken in advance of expected rain on June 7.  Rain began the night of June 7 and continued all day on June 8.  The rain was heavy at times during the day and some rain continued into the evening.  By the morning of June 9, 1.6 inches of rain had fallen.  The second round of sampling occurred on June 9 when the flow at North Whitefield was 1,260 cfs.  Peak flows were recorded on June 11.  The third sample was taken on June 14.  The flows were still very high on June 14 (at 1,190 cfs), but the river was already visibly less turbid.  Nutrients (Total N, Total P) and turbidity are presented in Table 3.  Water clarity was either observed, or measured in a turbidity tube.

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