Drnach Environmental Portable Flow Monitoring Protocol
Quality Control Program

  1. Prior to meter installation:
    1. Prior to installing the flow meter, Drnach Environmental will have met with the client and their engineer to determine if the site's hydraulic characteristics are conducive to collecting accurate flow data.  What Drnach Environmental is looking for are sites that exhibit non-turbulent laminar surface flows with adequate velocity to prohibit silting, but not so high as to create "rooster tails" of the flow as it passes over the meter's submerged sensor.  Drnach Environmental attempts to avoid drop manholes or manholes with multiple influent lines which may cause interfering turbulence for the velocity sensors.  We also avoid sites with extremely steep slopes, which tend to have high velocities and low heads.  Although silting is not a problem, shallow depth measurements and turbulence caused by the sensor itself tend to prohibit good flow measurements.
    2. All Information for the meter and sensor, i.e., serial number, is recorded for tracking purposes.
      (Pre-calibration form A1)
    3. The meter and sensor are cleaned, and all the desiccants are checked.
    4. Meter Specifications for meters Drnach Environmental uses are available below as downloadable and printable PDF files:

      Isco 2150 Flow Module
      Hach Sigma 910 Flow Meter
      Hach Sigma 920 Flow Meter
      Hach Sigma 930 Flow Meter

  2. Bench Calibration
    1. Bench calibrations consist of entering all site information and set-up information such as study name, line size, meter interval frequency, and adjusting real date and time. The sensor is then zeroed and calibrated in the Flow Calibration Flume.  The sensor is left in the calibration line and the depth is checked a second time no sooner than three minutes from the original calibration.  The sensor is then removed from the calibration line to observe its return to zero. All information is recorded on Pre-calibration form A1.
    2. The meter sensor is then connected to the appropriate size band or nozzle and loaded on the truck to be installed (typically within 24 hours).


  3. Installation
    Upon Identifying an "acceptable site" and immediately prior to sensor installation, the area is brushed, and measurements of the depth and velocity are taken. These readings are recorded on field form A2 and will be compared to the sensors output readings following installation. The meter sensors are then installed, cables are secured, and the flow meter itself is hung inside the manhole. Once acclimated to ambient temperature (5 - 15 minutes) the meter is accessed and depth and velocity readings are recorded. If necessary a second depth and velocity reading is taken to confirm the initial depth and velocity values. This is particularly important when flows are observed to fluctuate abruptly due to conditions such as upstream pump stations and variations experienced in the small lines serving small sub systems. At this point digital photos are taken and manhole inspection information is collected and recorded on the Manhole Inspection Forms. The site is then secured, marked, and closed until the next site visit.


  4. Site Visits
    All first site visits are conducted by Drnach Environmental field technicians within the first seven days of installation. Data collected from these newly installed meters is reviewed and evaluated to determine if the site has the proper hydraulic characteristics for obtaining good flow date. Of primary interest is the initial scatter graph of H/V data, and whether the site exhibits a hydraulic "finger print" which can be used in conjunction with the field readings to assess the meter's ability to provide repeatable data throughout the study period. Flow meters are inspected and interrogated at least once per week, and once every 14 days for meters in CSO's. Site visit information is recorded on Drnach Environmental field check sheets (Field Form A2). Visits may be required more often depending on storm events and site characteristics; i.e., large amounts of grease, silting, or debris.
    During each visit, the meter is downloaded, and head, velocity, and battery readings are recorded. Weather conditions and site hydraulic conditions will be noted it they are out of the ordinary (i.e., rain, surcharge, or oily flows.)  The site is then secured, and the raw data is returned to the office. The data is then imported into one of Drnach Environmental's report programs and evaluated for a number of parameters. First, is the sensor getting adequate head and velocity readings to calculate flows throughout the day? Secondly, is the scatter graph typical of a free flow condition, or some other condition which will lend itself to be measured? At this point, the scatter graph is printed out and provided to the field technician for use during field calibration checks. Assuming that the first week of data was adequate to produce a working scatter graph (no surcharging) and the site can be metered (reproducible data was obtained), the field technician will re-visit the site.  During subsequent sire visits, the meter is downloaded to the tech's laptop computer. Downloads are conducted first since any correction to the meter after connecting to the laptop can result in loss of data. After downloading the information, the technician then takes a current real time status reading and records the head, velocity, and battery readings. The real time head and velocity readings are then plotted on the initial scatter graph in the field to determine if the flow meter's sensor has experienced any drift since its initial installation. If it has not, then the meter is left to collect data until the next site visit. However, if the head/velocity relationship indicates that the initial hydraulic characteristics for the site are no longer being recorded, the technician will clean the sensor and re-measure the flow.  This measurement is then compared to the current status reading, and to the field scatter graph.  If the meter continues to indicate that it is incapable of reproducing the initial scatter graph or is not within 1/4 inch of the field measurement, the meter is removed and bench calibrated before it is re-installed.  This procedure occurs at every download, scrub, and battery check throughout the course of the flow study.
  5. CSO Site Visits
    In addition to the procedures described above, at Drnach Environental we realize that CSO sites are different from flow sites, and require special consideration when attempting to monitor overflows.  As part of our ongoing QA/QC program for CSO's, the following items are also considered:
    1. At each site visit, chalking of the overflow is performed for the purpose of identifying overflow events between visits.  This requires the physical site inspection of the CSO.
    2. All site and meter information is recorded on  the CSO Field Sheet.
    3. Overflow data collected at each interrogation is appended to an ongoing summary scatter plot report of head & velocity data, for the purpose of identifying sensor drift throughout the course of the study.
    The goal of Drnach Environmental is to install and manage the open channel flow meter so as to provide flow data which is as accurate as the site conditions and meter permit. We believe that we accomplish this goal through diligent monitoring and review of the data collected as stated above.