YSI SonTek RiverSurveyor, System Manual

Page: 76 / 194

SonTek/YSI Inc
RiverSurveyor System Manual (May 1, 2007)
64
5.1.2. Are there limitations to the discharge calculation?
RiverSurveyor systems cannot measure the entire river cross-section. The “unmeasured” areas
are depicted in
Figure 5-2
and explained below.
•
The minimum ADP and vessel depth requirements limit the depths into which the RiverSur-
veyor system can profile. These sections, typically near the start and end positions on the
opposite riverbanks, are called the
edges .
•
The mounting depth (i.e., transducer depth) and the ADP’s blanking distance leave a section
of water near the surface unmeasured. This area is called the top .
•
Potential data contamination in the last cell (e.g., the cell is partially or fully “touching” the
riverbed), or potential side-lobe interference at the end of the profile, leaves a section of wa-
ter at the bottom that is unmeasured. This area is called the
bottom .
The RiverSurveyor program computes discharge in the edges based on either a constant slope
bank (using a ratio-interpolation method) or a vertical wall. Discharge in the top and bottom sec-
tions is computed (based on the velocities in the measured section) using either a power-law
method or constant method. These methods are described within §
5.1.3
.
5.1.3. How do I calculate total discharge for the section using RiverSurveyor?
The RiverSurveyor program requires a few user entries to calculate total discharge for a section.
Discharge for the top and bottom areas is calculated based on velocities computed using the Ve-
locity Profile Extrapolation method described in §
5.2.2
. These estimates are automatically com-
puted during each discharge measurement.
Discharge for the left and right edges is calculated based on the currents near the sides of the
measured area. The values used in the edge discharge calculations can be input during either data
collection or post-processing. Most users will enter these values during data collection to reduce
any complications.
Figure 5-2. Cross-sectional areas not measured by the ADP