1. (a) A facility must include a means of accurate effluent flow measurement.
2. (b) An effluent flow-measuring device must have an open channel to allow for easy inspection, calibration, and cleaning.

3. (c) Flow measurement must use a combination of primary and secondary measuring devices.

   1. (1) Primary measuring devices.

      1. (A) A primary measuring device must include a weir or a flume.
      2. (B) A primary measuring device must have a non-corrosive ruler (staff gauge) that is graduated in no greater than 1/4 inch increments that are clearly visible.
      3. (C) A primary measuring device must be installed upstream of a secondary measuring device to permit the manual measurement of water depth.

   2. (2) Weirs.

      1. (A) A channel approach section to a weir must be straight for at least 20 times the maximum expected head on a weir.
      2. (B) The minimum height between a channel bottom and a weir crest must be the greater of twice the maximum expected head on the weir or a minimum of 1.0 foot.
      3. (C) The upstream edge of a weir must not be corroded.
      4. (D) The crest of a weir must be exactly level to ensure a uniform depth of flow.
      5. (E) The upstream face of a weir must be smooth and perpendicular to the axis of the channel in both the horizontal and vertical directions.

      6. (F) Upstream of a weir, there must be a secondary measuring device located a minimum distance of the greater of:

         1. (i) three times the maximum expected head on a weir; or
         2. (ii) the distance recommended by the equipment manufacturer.

   3. (3) Flumes.

      1. (A) A flume must be located in a straight section of an open channel.
      2. (B) A flume must be installed in accordance with the manufacturer's recommendations.
      3. (C) A flume must distribute the approaching flow evenly across a flow channel to preclude turbulence and waves.

   4. (4) Secondary measuring devices.

      1. (A) A secondary measuring device must measure the liquid level in the primary measuring device, and must convert this liquid level into a flow rate that is integrated to a totalized flow.
      2. (B) A secondary measuring device must be installed in accordance with the manufacturer's recommendations and in a manner that reduces turbulence and promotes laminar flow.
      3. (C) A secondary measuring device must include a display of the instantaneous flow rate and a means of reading the totalized flow.

Source Note:The provisions of this §217.33 adopted to be effective August 28, 2008, 33 TexReg 6843.