HYDRAź, a software product by PIZER Incorporated, is designed specifically for the analysis, design and management of sewer systems. The HYDRAź analysis philosophy has over 30 years of experience in modeling sewer systems. Carlson Hydrology Module uses HYDRAź as an alternative method to conduct hydraulic analysis of the existing storm sewer systems.
The HYDRAź Processing command is integrated into the Create/Edit Sewer Structure command. When you finish creating/editing a sewer network, click on Analyze by HYDRAź button on the top of the Create/Edit Sewer Structure dialog to issue the HYDRAź Processing. If the HYDRAź analysis goes successfully, a standard HYDRAź report will be shown and the hydraulic results will be displayed on the dialog.
The results from Carlson Storm Sewers and HYDRAź Processing are not exactly the same due to some differences in the hydraulic calculation shown as below.
There are four pipe cross-sectional shapes: circular, box, horizontal ellipse and vertical ellipse. Circular section is defined by its diameter, box section is defined by its hight and width, horizontal and vertical ellipse sections are defined by their rise, span, wetted diameter, equivalent diameter etc. Every cross section has its own hydraulic calculation method. Please refer to the documentation on Pipe Size Library for details.
HYDRAź considers all cross sections other than circular odd hydraulic cross-section, and defines them with a set of elevation/width pairs. Therefore different hydraulic calculation methods may be used.
Generally, when using only circular pipes in the system, the two hydraulic results are more similar.
Carlson Storm Sewers has four methods to calculate junction losses: Approximate Method, Dynamic Method, Fixed Head Loss and Energy-Loss Method. For Approximate and Dynamic Methods, you need to specify the loss coefficient.
HYDRAź uses the same formula as the Dynamic Method, which defines the junction loss as the dowstream velocity head multiplied by the junction loss coefficient, to calculate the energy loss in the manhole resulting from bends and drops. However the loss coefficients are fixed and defined as follows for flat bottom manholes.
| 0o | 45o | 90o | 135o | 180o | |
| Open Chanel Flow | 0.4 | 0.7 | 1.0 | 0.7 | 0.4 |
| Pressure Flow | 1.0 | 1.5 | 1.9 | 1.5 | 1.0 |
In Carlson Storm Sewers, the computation proceeds from the most downstream point toward the upstream points of the network. At the outfall, if the tailwater elevation is higher than the critical elevation, the starting HGL elevation is set to the tailwater elevation. If the tailwater elevation is lower, the starting HGL elevation is set to the the critical elevation for subcritcial flow, or set to the normal elevation for supercritical flow.
In HYDRAź processing, if the tailwater elevation is higher than the critical elevation, the starting HGL elevation is set to the tailwater elevation, otherwise the starting HGL elevation is set to the normal elevation.
In Carlson Storm Sewers, the bypassed flow at one inlet goes to the
next downstream inlet. In HYDRAź Processing, the bypassed flow
doesn't pass over and results in ponding at the inlet. This would lead
to a difference in the total flow inside the sewer network.
In Carlson Storm Sewer, the Rational method is used to compute the
catchment peak discharge. Inlet flow is determined as the individual
catchment peak flow, i.e. the
rainfall intensity is computed using the time of
concentration of the individual subbasin. Pipe flow is the runoff from
all upstream subbasins. Therefore, when the watershed consists of a few
of catchments, only at the most
upstream point is the catchment discharge directly used for the pipe
flow rate. For the flow in any downstream pipes, the time of
concentration is determined as the longest of the travel times to the
upstream end of the current pipe, the travel time includes the
catchment time
and the pipe travel time. This time of concentration is used in the IDF
curves to obtain the rainfall inetersity for the Rational
formula.
In HYDRAź Processing, the pipe travel time is not considered.
In Carlson Storm Sewers, the storm sewer network is solved using the
standard step gradually
varied flow methods. This is an iterative procedure
used to determine the energy and hydraulic terms at the end of each
pipe. The direction of computation is from the most downstream pipe of
the network to the most upstream pipe. HYDRAź Processing may have used
other methods which could lead to a difference in the result.
Create/Edit Sewer Structure dialog: Fill
in
values.
Pulldown Menu Location: Network > Create/Edit Sewer Structure
Keyboard Command: putswr or
editswr
Prerequisite: a sewer file
(.SEW), a surface file (.TIN, .GRD)...\USER\RainLib.dta,
...\USER\inlet.dta, ...\USER\pipesize.dta
(mpipesize.dta in Metric unit), ...\USER\swrStruct.dta,
...\USER\paven.dta, ...\USER\pipen.dta, ...\USER\runoff.dta
File Name: \lsp\cntr_grd16.arx