The Scatter Report graphically displays the correlation between two (2) variables (sensor input) using Cartesian coordinates. Typically, depth and velocity readings are compared. Scattergraphs can give valuable insights into the condition and performance of both the pipe and the sensors.
From the Monitoring Station pop-up menu, select the bottom icon (Analysis Tools) and Scatter Report from the drop-down menu. Alternatively, you can select Scatter Report under Tools in the hamburger menu, in which case you would have to define the Organization, Project, Service, and Monitoring Station in addition to the configurations noted below.
In order to generate a scatter report, the report parameters must be specified in the “Configuration” tab (required fields are marked with a red asterisk). Pipe diameter, roughness coefficient, and pipe slope default to those entered under “Attributes” in Station Details; if these have not yet been defined, or if alternate values are being used, the drop-down menus allow for user inputs. The user also defines the time range or entire range to be used to generate the scatterplot. Note: the user has the option to exclude specific dates or date ranges.
Under “Scatter Plot Curves Configuration,” the user may further detail:
- General Scattergraph;
- Analysis Method;
- Froude Number; and
- Iso-Q Lines.
These configuration options are explained below.
1. Scatter Graph
The user may assign data from a specific sensor to the X and Y axes of the scattergraph. Typically, these are depth (Y axis) and velocity (X axis). Manual measurements used to calibrate either sensor, if available, may also be displayed on the scattergraph.
The user may also achieve insights through applying a color-ramp to the data points. “Simple” is the default value and displays a single color for all data points. “Two Color” takes the time extent of the data being analyzed, and divides into two (2) timeframes. The “Rainbow” option adds further resolution to the timeseries of data.
2. Analysis Method
The Manning Equation is the central feature of the scattergraph, describing the relationship between depth and velocity under ideal conditions. The Manning Equation generates a pipe curve against which monitoring data can be compared and assessed. The scatter plot configuration allows for three (3) different analysis methods applying the Manning Equation:
- Design Method (DM): this standard application, the design pipe curve of the sewer, relates depth and velocity using a specified roughness coefficient and pipe slope as detailed by the sewer system designer.
- Lanfear-Coll (LC): this method fits the Manning Equation to monitored data without direct reference to pipe slope or roughness coefficient. The resultant pipe curve is compared to actual data (under uniform flow conditions) and used to estimate the full-pipe capacity of the sewer.
- Stevens-Schutzbach (SS): this is an iterative regression technique that fits the Manning Equation to flow monitoring data, with special application for non-uniform flow conditions caused by downstream obstructions. The Stevens-Schutzbach pipe curve is not constrained to the origin (0,0), unlike the Design and Lanfear-Coll methods (thereby accounting for the dimensions of the obstruction).
Note: if the monitoring data does not line up to any of the three methods’ pipe curves, the user is alerted that either (1) the sewer was not experiencing uniform flow conditions during that period, or (2) the monitoring sensors are not making valid depth or velocity measurement (e.g., sensor drift).
3. Froude Number
The Froude number (Fr) denotes the flow conditions within the sewer:
- Fr < 0.7: flow conditions are subcritical (generally slow, tranquil flow)
- Fr 0.7 < 1: flow conditions are transitional (potentially unstable) and subcritical
- Fr = 1: flow conditions are critical
- Fr 1 < 1.5: flow conditions are transitional (potentially unstable) and supercritical (generally rapid, fast flow)
- Fr 1.2 < 1.7: development of undular hydraulic jumps (waves) without breaking
- Fr > 1.5: flow conditions are supercritical
- Fr 1.7 < 2.4: undular hydraulic jump breaking
- Fr > 2.6: diminishment of undular hydraulic jumps
Note: generally, monitoring is avoided at locations with hydraulic jumps and waves.
4. Iso-Q Lines
Iso-Q lines are depth-velocity points resulting in a constant flow rate, interpreted similarly to elevation contour lines on a topographic map. These are typically used to denote percentages of full-pipe capacity at actual flow rates, and are useful for visualizing the capacity. DataCurrent defaults with Iso-Q lines at 25%, 50%, and 75% capacity; further Iso-Q lines can be defined and added by the user.
The Scatter Report displays the scatterplot within a graphical display of the sewer dimensions, including the pipe curves of all three methods, Froude number curves, and Iso-Q lines.
The Scatter Report further notes key measurements in tabular format:
- the hydraulic coefficients of each of the three (3) methods of applying the Manning Equation
- the nominal pipe capacities as calculated using each method
- the maximum velocity as calculated using each method
- the correlation coefficient representing the proportion of variance between the method’s pipe curve and actual measured data
- for the Stevens-Schutzbach method, the depth of the downstream obstruction, if applicable