This dataset contains measurements of water parameters at four sites on the Choptank River and four sites on the Pocomoke River; all sites are in Maryland, U.S.A. The measurements were made for the purposes of understanding how tidal hydrology influenced turbidity during high and low non-tidal river discharge. The four monitoring locations on each river were chosen as representative of the upper tidal freshwater estuary (the farthest upstream extent of tide), the lower tidal freshwater estuary (just upstream of the oligohaline estuary), the oligohaline estuary, and the mesohaline estuary.
At all eight water monitoring locations, we deployed a solar powered, cellular-enabled, water monitoring station based on the design of Stroud Water Research Center’s EnviroDIY initiative (https://www.envirodiy.org). A Meter Group Hydros 21 Conductivity, Temperature, and Depth sensor (CTD sensor; https://metergroup.com/products/hydros-21/) and Yosemitech 511 turbidity sensor (http://e.yosemitech.com/TUR/Y511-A.html) were installed at one end of a PVC pole that pivoted on a bolt affixed to a piling. This allowed the sensors to be pivoted out of the water for cleaning and maintenance and could otherwise be locked at a fixed elevation above the river bed. The sensors were deployed in the deepest water possible while accommodating the safety of boats and people using the dock. Sensors were queried by a Mayfly Data Logger (https://www.envirodiy.org/mayfly/hardware/) at 10 minute intervals and stored to an onboard memory card, and those data were transmitted via cellular modems to the Monitor My Watershed Data Sharing Portal (https://monitormywatershed.org) for instant and public viewing. The Mayfly Data Logger, battery, and cellular antenna were protected inside a waterproof box and wired to an external solar panel. Except at the mesohaline sites, a TCM-4 Tilt Current Meter by Lowell Instruments (https://lowellinstruments.com/products/tcm-4-tilt-current-meter/) was deployed independently from the dock in the deepest water that could be reached. A 12 inch by 12 inch by 1 inch thick cement paver with a hole drilled through the middle was used as an anchor for the current meter; a chain was also attached through this hole so that it could be retrieved from the dock. The flow direction (ebb current versus flood current) measured by the Lowell Instruments TCM-4 tilt current meters was interpreted using the instruments’ reported magnetic compass heading (degrees) and map-based measurements of the channel axis at each deployment location. When the TCM-4 tilt current meter reported a compass heading of plus or minus 90 degrees from the down-estuary channel axis (ebb tide), the corresponding current velocity was assigned a positive value. When the TCM-4 tilt current meter reported a compass heading of plus or minus 90 degrees from the up-estuary channel axis (flood tide), the corresponding current velocity was assigned a negative value.
The Meter Group Hydros 21 CTD sensor, Yosemitech 511 turbidity sensor, and Lowell Instruments TCM-4 tilt current meter were periodically removed from the water to clean biofouling growth. The date and time of cleanings are noted in the data file and were usually associated with an independent check of the conductivity and turbidity sensors. These checks were performed using a Yellow Spring Instruments 6920 sonde with temperature, conductivity, and turbidity sensors. The conductivity and turbidity sensors on this sonde were calibrated with standards prior to each field trip and calibration was checked after returning from the field.
Aquarius Time Series (www.aquariusinformatics.net) was used for data quality control. The predominant data quality control action was to delete data that appeared to reflect fouling of a sensor. When the sensors were out of the water, all parameters except water level were deleted, and water level was amended to zero during these periods. Although the quality of current velocity measurements was affected by fouling and low water, data were not deleted because we presumed that the occurrence of slack current at high and low tides could still be accurately discerned from the data. Sensor drift was evaluated using best professional judgement, the timing of sensor cleaning events, and measurements made with the YSI 6920 sonde; questionable data were deleted. Each value was assigned a grade based on best professional judgment and available quality control measurements. Measurements of temperature that were within 10% or 2 degrees Celsius of the Meter Group Hydros 21 CTD sensor were considered good, and values outside this range were considered fair, poor, or unusable (if a fouling trend was suspected). If graded poor based on a quality control measurement, subsequent measurements were also graded poor until the next quality control measurement that indicated good agreement. This process was followed for specific conductivity (within 10% or 20 uS/cm of quality control measurement) and turbidity (within 10% or 10 NTU of quality control measurement). Conductivity quality control measurements at both oligohaline sites were not deemed to be accurate because the sonde was calibrate with a low range standard instead of a high range standard. Grades (good, fair, poor) pertain to the corrected data (not raw).
No quality control was performed on the tilt current meters. Measurements were graded good, fair, poor, or unusable based on best professional judgement and the dates of sensor cleaning.
The upper tidal freshwater estuary of the Choptank River was measured at 38.927081 N, 75.828191 W and was accessed through private property and a private dock with permission of the owner. The Meter Group Hydros 21 CTD sensor was deployed 0.55 m above the river bed. Thus, water depth at the location of sensor deployment can be calculated by adding 0.55 m to the depth measurement from the sensor, but sometimes the sensors were exposed to the air during low tides. If water depth in the channel was less than 0.55 m, the sensors were out of the water.
The lower tidal freshwater estuary of the Choptank River was measured at 38.823579 N, 75.863997 W and was accessed through private property and a private dock with permission of the owner. The Meter Group Hydros 21 CTD sensor was deployed 0.21 m above the river bed. Thus, water depth at the location of sensor deployment can be calculated by adding 0.21 m to the depth measurement from the sensor, but sometimes the sensors were exposed to the air during low tides. If water depth in the channel was less than 0.21 m, the sensors were out of the water.
The oligohaline estuary of the Choptank River was measured at 38.743076 N, 75.99373 W and was accessed through private property and a private dock with permission of the owner. The Meter Group Hydros 21 CTD sensor was deployed 0.57 m above the river bed. Thus, water depth at the location of sensor deployment can be calculated by adding 0.57 m to the depth measurement from the sensor. The location of measurement is on the outside of a large meander bend, and current velocity measurements are dominated by a persistent up-estuary circulation pattern. Data users should interpret the current direction and velocity measurements from this station with this in mind.
The mesohaline estuary of the Choptank River was measured at 38.585006 N, 75.980209 W and was accessed through private property and a private dock with permission of the owner.
The upper tidal freshwater estuary of the Pocomoke River was measured at 38.17895 N, -75.39408 W, and was accessed on a public dock immediately upstream from the Highway 12 bridge. The Meter Group Hydros 21 CTD sensor was deployed 2.44 m above the river bed. Thus, water depth at the location of sensor deployment can be calculated by adding 2.44 m to the depth measurement from the sensor. The TCM-4 Tilt Current Meter was deployed on the north side of the channel (opposite side of the channel from the Hydros 21 CTD sensor and Yosemitech 511 turbidity sensor). This was necessary to avoid strong secondary currents that appeared to exist on the south side of the channel.
The lower tidal freshwater estuary of the Pocomoke River was measured at 38.823579 N, -75.863997 W, and was accessed from a public dock at the Pocomoke River State Park: Milburn Landing. The Meter Group Hydros 21 CTD sensor was deployed 0.55 m above the river bed. Thus, water depth at the location of sensor deployment can be calculated by adding 0.55 m to the depth measurement from the sensor.
The oligohaline estuary of the Pocomoke River was measured at 38.04451 N, -75.66185 W, and was accessed through private property to a private dock with consent of the owners. The Meter Group Hydros 21 CTD sensor was deployed 1.82 m above the river bed. Thus, water depth at the location of sensor deployment can be calculated by adding 1.82 m to the depth measurement from the sensor. Due to the depth of deployment and the possibility of density stratification at this site, the TCM-4 Tilt Current Meter measurements made at the bottom of the channel may not reflect the flow velocity or direction at the surface of the water column.
The mesohaline estuary of the Pocomoke River was measured at 37.97935 N, -75.63943 W, and was accessed from a public dock. The Meter Group Hydros 21 CTD sensor was deployed 0.60 m above the river bed. Thus, water depth at the location of sensor deployment can be calculated by adding 0.60 m to the depth measurement from the sensor.
