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The Sheepscot River Turbidity Pilot Study, - page 5 / 12

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On May 16, heavy rain was reported in the Sheepscot River watershed.  Over 1.5 inches was recorded by 5:00 pm.  Samples were taken from 10 sites from 2:25 pm to 8:00 pm the afternoon of the 16th.  The Sheepscot River stream gauge (at North Whitefield) went from 280 cfs on the morning of the 16th (essentially the same as the 66-year median for this day) to 520 cfs during the evening of May 16-17 (USGS Real-Time River Gauge Data for Maine website, the Sheepscot River gauge is at North Whitefield).  The samples coincided with the rising river stage near the time of maximum flow.  The turbidity/TSS results are arranged by river branch and sample sites in Table 1.  The upper Sheepscot mainstem above Long Pond and the upper West Branch above Route 3 have low turbidity.  Turbidity values in the 1-2 NTU range could appear to a casual observer as clear water.  Sediment sources on the mainstem are apparent below Long Pond.  The lower West Branch is also muddy, but less so than the mainstem.  The increased turbidity on the mainstem as observed at North Whitefield must be coming from the mainstem.  On the West Branch, Meadow Brook is a strong sediment source, but it is greatly diluted by the West Branch as observed at Weeks Mills.  Choat Brook is turbid, but is relatively clean compared with the West Branch.  There are additional sources of turbidity between Windsor Station and the Howe Road.

Table 1.  Total Suspended Solids (TSS) and Turbidity for SVCA samples of May 16, 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

<2

1.3

Hatchery

<2

1.1

Meadow Br

23

27

Coopers Mills

26

22

Weeks Mills

15

13

No Whitefield

18

26

Choat Brook

8

5.2

Alna

32

25

Windsor Station

10

11

Howe Road

16

17

Essentially the same areas were sampled by SVCA on October 12-13, but at eight sites.  Heavy rain began on the evening of October 11, with 1.1 inch being recorded as of 8:00 am on October 12.  Rain continued through the day, but was almost over by 1:15 pm when 1.6 inches of total rain was recorded.  On October 13, the river gauge at North Whitefield peaked at 557 cfs (an increase from 72 cfs on October 11, USGS website).  The samples were taken during the late afternoon on October 12, on the rising river stage near the peak, or during the early morning of October 13 at the peak flow.  The sample sites and the TSS and turbidity results are given in Table 2.  Again, the upper West Branch and mainstem are relatively clear.  On the mainstem, the river still has relatively good water quality at Coopers Mills, but it receives a lot of turbidity from the

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