Section 4 - Drainage Computation

SETTING GLOBAL STORM EVENTS AND ALTERNATIVES

VALIDATE

COMPUTATION AND RESULTS

 

 

SETTING GLOBAL STORM EVENTS AND ALTERNATIVES

Drainage and Utilities calculations are run on groups of settings called Scenarios, which have distinct subgroups of settings focused on aspects of drainage design or analysis. The subgroups are called Alternatives and include scopes as Physical Alternative, Design Option Alternatives and Rainfall Runoff Alternatives (focus here). Each Rainfall Runoff Alternative points to a Storm Event selected from the Storm Data collection (the IDF-Table imported previously).

Scenarios will be discussed in some more detail later in this workflow. More specific information is available on the Bentley Learn Server - ORD CE - 09 - Drainage Modeling and ORD CE – 10 – Drainage Hydraulics learning path.

Storm Events used for analysis and design of storm drainage systems are usually:  

• 2-year for water handling
• 10-year for the drainage system and
• 25-year and/or 50-year for sag condition

(See Table 11-2 Pavement Drainage Design Criteria, Chapter 11 – CTDOT Drainage Manual)

1. Select the Components tab, click on Storm Data, click on Global Storm Events. You should see one Alternative - Base Rainfall Runoff. 

2. Click inside the Global Storm Event box for Base Rainfall Runoff. 

3. Click on the ellipsis (…) and select the IDF_Table_Prj_No_XXX_YYYY created previously and the year you would want as your base rainfall runoff and click Close. 

4. Close the Global Storm Events box.

5. Select the Analysis tab, here tools are combined to calculate and report on the drainage scenarios.  

As shown in Section 1 - Introduction and Tools, the Analysis tab is split into three (3) sections: Calculation, Analysis Tools and Analysis Views. Most tools in the Calculation section are also available in the Compute Center box from the Analysis Tools section.

Select the Scenarios icon, there are two Scenarios: Base Design and Base Analysis. 

Base Design will resize pipes, change inverts to Default Design Constraints as described in Section 2 - Getting Started. 

Base Analysis will not resize pipes or change inverts but will check if pipes and inverts conform to Default Design Constraints. Any discrepancies will be shown in ‘User Notifications’ after verified or computed. 

1. Click on the Scenarios icon for the Scenarios box to open.

2. Select the Base Analysis, right-click and click on Properties, click on the Hydraulic Analysis tab in properties.

3. Click on Rainfall Runoff, click on the down arrow next to Base Rainfall Runoff and click <New…>.

4. In the Create New Alternative box enter a new rainfall alternative for your Project: Base Analysis - 2-yr Storm, click OK.

5. Select <New…> again add more Rainfall Alternatives as needed:

• Base Analysis – 10-yr Storm,
• Base Analysis – 25-yr Storm,
• Base Analysis – 50-yr Storm

6. Select the Base Analysis you want to run, example: Base Analysis - 10-yr Storm. Close the properties box. Close the Scenarios box. 

7. Select the Components tab, click on Global Storm Events. There are now additional alternatives.

8. Change the Global Storm Event to the projects corresponding event storms (2-yr, 10-yr, 25-yr and 50-yr). For Base Analysis – 2-yr Storm click on down arrow and select:  IDF Table_Prj_No_XXX_YYYY – 2 Year. Repeat for each Base Analysis and Storm.

9. Select the Analysis tab and select the Scenarios icon. Right-click on Base Design and select Properties. Click on the Hydraulic Analysis tab.

10. Change the Rainfall Runoff to the Base Analysis as previously. Example: Base Analysis – 10-yr storm. Close the properties box.

This is the minimum preparation needed to Compute the storm drainage system(s) for a project.

 

VALIDATE

The Validate command is in the Analysis tab – Calculation section and within the Compute Center menu box. The Validate command will run a diagnostic check on the network data (drainage system) and alert you to possible problems that could be encountered during the calculations. This is a manual validation and checks only for input data errors. The Compute command is the automatic validation that Drainage and Utilities runs when it is initiated, and it will check for input data errors and for network connectivity errors as well as many other things beyond the manual validation checks. It is a good idea to first check (validate) the drainage system for any input data errors or missing items/data especially when there is a large system. This may need to be done multiple times, because some errors may be hidden after the initial validation.

Click on the Validate command, you will/may get a message for errors or warnings: Click OK.

After the validation is complete you will probably see two different kinds of markers in your 2D view window (usually View 1, Default).

Click on Notifications or the User Notification icon in the Compute Center.

The notifications window will come up displaying a list of warnings generated during the validation process. There are two types:

Red error must be corrected before the model (system) can be computed.

Yellow does not prevent successful calculation of the model, but element does not meet certain criteria.

In the user Notification box, you will see messages with the RED and/or YELLOW icon as well as a toolbox (see below).

» Example of User Notifications:

Message:  The calculation option Structure Loss Mode must be set to EGL in order to use the HEC-22 Energy (Third edition) Headloss Method.

Meaning:  Inlet calculations use the Headloss Method: HEC-22 Energy (3^rd Edition) to use this, the Structure Loss mode must be set to the Energy Grade Line (EGL) in the Calculation Options.

Solution:  Analysis tab, Options, Right-Click on Base Analysis, Properties. In the properties box, select Structure Loss Mode and select Energy Grade.

» Some more examples:

Message — Meaning — Solution:

There is no gutter leaving this ‘On Grade’ catch basin.  Bypassed flow is directed to the subnetwork outfall.  —  The catch basin doesn’t have a gutter attached.  —  Open the Analytical View and place a gutter to direct the flow to next catch basin or system. If going to overland flow (no curbing) you can disregard. 

Conduit does not meet minimum cover constraint.  —  The min. cover that is set in Default Design Constraints is not met.  —  Change the inverts, or size or add barrel if possible, or ignore for calculations and use Class V RCP for callouts and estimating.

Structure and pipe inverts do not agree with selected benching type. — Benching method is set to HEC-22 Benching Method = Flat in accordance with the CTDOT Drainage Manual. — You can disregard this message.

 

COMPUTATION AND RESULTS

» COMPUTE

You are ready to compute after all RED issues are resolved and all YELLOW issues are modified or considered.

1. Click the Compute icon.

Drainage and Utilities will run the calculations, you will see some windows pop-up, wait until the GVF-Rational Calculation Summary box opens.

2. Calculations were successful if you see: Convergence was achieved in the Calculation Executive Summary box.

3. Click on Messages… to see the newest User Notifications, if there is an error, the calculations will stop at that point, you will have to solve the error and rerun calculations.

4. Click on Report and for the Scenario Summary preview, this can be printed.

5. Click Details… the Calculation Detailed Summary box will open showing: 

• Calculation Options
• Catchment Summary
• Link Summary
• Node Summary
• Inlet Summary
• Pond Summary

6.  Click on Report to get one combined report to review/print/save. For individual and more complex reports use Flex Tables.

» FLEX TABLES

Drainage and Utilities shows the engineering data in tabular format called Flex Tables. The most common flex tables have been established as CTDOT Flex Tables have been formatted to follow the CTDOT Drainage Manual. Any flex table can be edited to best fit the project. The designer should use the drainage manual as a guide to determine the information needed to represent the drainage system.

Click the Flex Tables icon in the Analysis Views section. In the Flex Tables box click on the Hydraulic Analysist ab. Tables are characterized into Hydraulic Model — Shared — Predefined.  

Drainage and Utilities has ‘predefined tables’ set-up that can be edited as needed.  Expand the Tables – Hydraulic Model folder, here CTDOT Flex Tables are available for use and are formatted to show all information and data required. Should you have to edit to reflect information/data needed for the drainage computations, they still can be edited as needed specific to the project. Copy the flex table and rename project specific.

CTDOT Gutter Flow Analysis, CTDOT Gutter Flow Analysis at Low Point and CTDOT Strom Drain Computation Sheet follows the computation sheets of the CTDOT Drainage Manual Chapter 11.

Double-Click on a flex table to open it. Each table has various tools such as: export, copy, paste, edit, zoom to, report, options and select in drawing.

Export to File… — creates a text or csv file to work within Excel or shape file if needed.

Edit… — allows columns to be added or removed from the flex table. Example: scroll in the Available Columns to X, click on Add. Now X is added to the Selected Columns side and click OK. X column is added to the catch basin flex table.

Zoom To… — highlight a row and click on Zoom To, the active view will zoom in to the item/row selected and is highlighted.

Report… — creates a report that can be printed. Paper size and page set-up can be edited in the report page.

Options... — gives the ability to create selection sets. 

Create Selection Set — can be used to filter various items. As example to split up the drainage data into left and right side of the roadway. 

• Within the catch basin flex table select the catch basins for the left side of the roadway (highlight all left CBs using the CTRL key).

• Click on the down arrow next to Options and select Create Selection Set…, type in selection set name: RteABC-LT. Click OK.

• Repeat these steps for the catch basins on the right side of the roadway.

• Click on the Utilities View tab and click on Selections Sets, click on Hydraulic Analysis tab. Here all Selection Sets for the project are stored.

 

» PROFILE FOR DRAIANGE

- SINGLE PIPE PROFILE

You can view the profile of any single pipe between two drainage structures by right-clicking on the pipe and hovering over for the pop-up menu to come up and picking the Open Profile Model bottom, it will ask to Select or Open View to place the Profile of the pipe.

- PROFILE RUNS

Profile Runs show hydraulic information such as Hydraulic Grade Line (HGL) and/or Energy Grade Line (EGL), show the depth of cover, and show whether slopes of conduits are in the same direction and magnitude as the road design.

Hydraulic Run From Node: will create one profile run from a selected node to the outfall, or between two selected nodes.

Hydraulic Run To Outfall: will create a profile run for every path, from farthest upstream node to the outfall. This tool will create profile runs for each run to the system outfall. When completed there will be 2 or more profile runs depending on the system.

Utility Run From Links: will create a profile run from selected links, for any type of utility (storm, communication, sanitary, electric, water). The links must be consecutive without gaps between them.

 

Project Run: This will project a previously created profile run onto a linear element such as a centerline or another profile run. Great tool to show the drainage structures and pipes on the road's centerline profile (vertical alignment).

In the Explorer, expand Profile Runs (click on down arrow); the newly created profile runs are now available to view. Right-click on the run to see all available options to view/edit the profile data.

Open Profile Model – right-click on a Profile Run, select Open Profile Model – click in the view window to place the profile run.

Open Analysis Profile - right-click on Profile Run, select Open Analysis Profile - a window opens with the analysis profile. This can be modified to include Hydraulic Grade Line (HGL), Energy Grade Line (EGL), labels and table annotation and legend. The file can be exported to a drawing or can be printed. 

saved as a pdf-file

Open Engineering Profile – right-click on Profile Run, select Open Engineering Profile - a window opens with the engineering profile. This can be modified to include inverts, slopes, types, length and more. The file can be exported to a drawing or can be printed and exported to a document.