In addition to the YSI information collected as in previous years, this file includes depth measured by the Sigma Autosampler. We generally rely on depth measured by the YSI, as these are more reliable. We rely on the Sigma measurements for discharge for the last nine days in December 2004.
YSI: YSI 6200 data sondes were deployed vertically in a pool deep enough to contain water during dry conditions. The 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 good quality because detritus did not accumulate in the bottom of the pool (unlike our suburban site).
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 oxygen, pH, conducitivty and depth was performed roughly every 4-6 weeks. Instrument drift during deployment periods was not significant.
SIGMA AUTOSAMPLER: Depth is also recorded at times using a depth sonde integrated with the Sigma autosampler. Sonde was secured to cinder block driven into the stream bottom and referenced to standardized depth. Discharge reported by the Sigma is included for when the autosampler was programmed to sample on a flow weighted basis. Sigma discharge is based on a rating curve programmed into the Sigma that is based on the old rating curve developed prior to 2004 and is therefore approximate.
When available, YSI depth is used in preference to Sigma depth to determine discharge because the latter is less reliable. Sigma depth is used for discharge from from 2004-12-23 to 2004-12-31. Sigma depth is referenced to YSI depth based on overlap of readings prior to Dec 23 2004, and then further corrected to the HOBO depth. YSI_Depth = Sigma_Depth - 0.032. HOBO_Depth = YSI_Depth + 0.17549. Discharge when Depth_Device = SIGMA should be used with caution because of instrument unreliability and the several conversions that are made to standardize the depth.
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 Cart Cr. and is located in Newbury MA. Some residential area is present. (~ 10% of the basin). In addition, I-95 passes through the center of the catchment, resulting in roughly 8% impervious surface area
STATION STATE X STATE Y
YSI-CC 247680 946790
NOTES AND COMMENTS:
Velocity measurements were made using a Marsh McBirney current meter. Discharge estimates in Cart Cr. are based on a power rating curve that contains measurements up to a depth of 0.8 meters, as standardized to depth measured with a HOBO datalogger (Column = HOBO_Depth), which is above bankfull stage. Rating curve has been standardized to HOBO_Depth to allow application of a single rating curve across years. Rating curve has an R2 of 0.96 using 32 measurements between 2001 and 2007. All files in this series (2001-2006) 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:
Discharge rating curve :
Discharge (l/s) = 731.91 (depth) ^ 5.5172
where depth is HOBO_Depth
