Depth and water temperature were measured using a HOBO data logger deployed in a stilling well.

Depths are corrected for barometric pressure changes using readings in an additional HOBO datalogger deployed at Marshview Farm. The HOBO is deployed in a a PVC tube, which was attached to ree-bar driven into the stream bed. The PVC tube has holes drilled to allow adequate water circulation.

ADDITIONAL RESEARCH LOCATION COORDINATES: In addition to the decimal degree coordinates given above, locations are also given here in Massachusetts State Plane coordinates. The stream is called SawMill Br. and is located in Burlington MA. Small amounts of forest remain (~14% in 1999), much of which is along the stream channel near the gaging site.

STATION STATE X STATE Y
YSI-SB 225840 919310

NOTES AND COMMENTS:
Velocity measurements were made using a Marsh McBirney current meter. Discharge estimates in Saw Mill are based on a power rating curve that contains measurements up to a depth of 1 meter, which is above bankfull stage. Rating curve has an R2 of 0.96 using 24 measurements between 2001 and 2007. Rating curve has been standardized to HOBO_Depth to allow application of a single rating curve across years. All files in this series (2001-2007) are currently standardized to HOBO_depth.

The column Depth_Device is included when combining files from several years, over which several different devices were used to calculate depth. HOBO_Depth is the depth that is standardized across all measurement devices so that a single rating curve can be applied.

CALCULATIONS:
Velocity measurements were made using a Marsh McBirney current meter and starting in 2009 with a Sontek Flowtracker. Discharge estimates in Saw Mill are based on a power rating curve that contains measurements up to a stage depth of 1.2 meters, which is above bankfull stage. Rating curve has an R2 of 0.89 using 40 measurements between 2001 and 2009. The rating curve has not noticeably changed over the period. Prior to 2007, stage was measured with various other instruments (YSI, Sigma depth sonde, HOBO). All files in this series (2001-2009) are now standardized to HOBO depth. The rating curve is based on the standardized HOBO depth's (and actual HOBO depths since 2007).

CALCULATIONS:
Discharge rating curve :
Discharge (l/s) = 889.65*depth^5.8788
where depth is Adj_HOBO_Depth

Adj_Hobo_Depth is a corrected HOBO depth that represents the true hobo depth (StandardizedHoboDepths in previous years). We started having problems with sand accumulation in the stilling well, and following downloads, redeployment of the HOBO caused it to sit on top of the sand. Manual measurements of water depth were used to make the correction. Starting in 10/21/09, we plan on preventing this from happening any longer. The following corrections were applied:
1. 2006-07-26 - 2007-04-03: 0 m
2. 2007-04-03 - 2007-04-18: 0.035 m
3. 2007-04-18 - 2007-05-23: 0.055 m
4. 2007-05-23 - 2008-06-06: 0.072 m
3. 2008-06-06 - 2009-01-14: 0.0446 m
4. 2009-01-14 - 2009-10-21: 0.0957 m
5. 2009-10-21 - yyyy-mm-dd: 0

Adj_HOBO_Depth is equivalent to StandardizedHoboDepths in previous years.

Also, at times depth and discharge may be periodically erroneous due to leaf pack accumulation at a riffle downstream causing backup. We remove this whenever we visit the site. Generally we believe the depth error is on the order of 2-4 centemeters. The depth data have not been corrected for errors associated with temporary debris dams.