This file consists primarily of depth data collected using four approaches: 1) A hobo data logger temporarily deployed Jan 6 - March 8, 2006 (TEMP_HOBO), 2) A HOBO datalogger deployed in a stilling well from July 26th - Dec 31st 2006, 3) Sigma Autosampler Jan 1-2, 2006 and Mar 8 - Apr 22nd, 2006, 4) YSI depth sonde Apr 22nd - July 26th 2006. Depths were standardized to the HOBO measurement in order to create a consistent data set that is applied to the standard rating curve. Depth were standardized either using simultanous readings of the instrument, or by comparing instrument measurement and manual stage height reading at the YSI stilling well.

YSI 6200 data sondes were deployed vertically in a pool deep enough to contain water during dry conditions. Discharge from Sigma depth measurements should be used with caution due to periodic unreliability of the readings.

YSI: The YSI sonde was deployed in a PVC tube, which was attached to ree-bar driven into the stream bed. The PVC tube had holes drilled to allow adequate water circulation. Dissolved oxygen measurements are of poor quality because the the bottom of the pool was often filled in with detritus following intermediate sized storms, leading to anoxic conditions. To alleviate this problem, the PVC tube was raised 10.1 cm on 7/16/03. This file includes the raw depth measurement (RAWYSI_Depth), as well as the depth measurement corrected to the YSI depth after the change in tube height (YSI_Depth_STD). In this file they are the same (maintained from earlier years).

The PVC tube was surveyed upon original deployment in 2001 and resurveyed in 2002 to ensure that elevation did not change during winter ice period. No change was detected. No evidence of change has been noted through 2006 based on discharge measurements. See discussion below for development of the discharge-stage relationship.

Recalibration of conducitivty and depth was performed roughly every 4-6 weeks. Instrument drift during deployment periods was not significant.

StandardizedHoboDepths = YSI_Depth_STD + 0.21

SIGMA AUTOSAMPLER: Depth is recorded using a depth sonde integrated with the Sigma autosampler. Sonde was secured to cinder block driven into the stream bottom and the measured depth referenced to YSI depth. When available, YSI depth is used in preference to Sigma depth because the latter is less reliable. Sigma depth is referenced to HOBO depth based on overlap of HOBO, YSI and Sigma measurements, and using manual stage measurements at the YSI installation. Discharge using Sigma depth should be used with caution because of instrument problems and a less stable mount on the stream bottom, though an effort was made to provide a reasonable depth/discharge estimate that can be used to compare across instruments/times.

StandardizedHoboDepths =SIGMA_DEPTH + 0.237

HOBO Datalogger: Depth and water temperature are recorded by the HOBO data logger. Depths are corrected for barometric pressure changes using readings in an additional HOBO datalogger deployed at Marshview Farm. Between Jan and March 2006, a borrowed data logger was deployed attached to a cinder block placed on the stream bottom, but should give consistent measurements during the deployment.. A newly purchased HOBO data logger was deployed in a permanent stilling well in July 2006. 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.

The temporary HOBO is standardized to HOBO depth using comparison with periodic stage height measured manually at the YSI stilling well:

StandardizedHoboDepths =TEMP_HOBO + 0.227

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 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 StandardizedHoboDepths

A flow reading that was reported by the Sigma is also included. Sigma flow was calculated using a rating curve programed into the Sigma using an old rating curve. This is used for reference to the nutrient sampling performed by the Sigma when programmed under a flow-weighted program. The column Depth_Device is included when combining files from several years, over which several different devices were used to calculate depth.

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.