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Use Autodesk’s Civil 3D and SSA to Illustrate and Solve Stormwater System Deficiencies

Use Autodesk’s Civil 3D and SSA to Illustrate and Solve Stormwater System Deficiencies

A rainy day may seem like just an inconvenience, but it can drastically affect safety and the environment. Stormwater poses environmental and safety threats as it carries materials into rivers or streams such as litter, road salt or chemicals from lawns and gardens. It also can cause flooding on roadways, creating unsafe driving conditions, as well as sanitary sewer overflows that contaminate rivers and streams. 

These risks resulted in the Environmental Protection Agency’s (EPA’s) regulations to control polluted stormwater runoff. The challenge for municipalities is to address these stormwater concerns while remaining compliant with the National Pollutant Discharge Elimination System (NPDES) permit requirements – that’s where B&N’s Storm Sanitary Analysis (SSA) and Civil 3D come to play.

What are Civil 3D and Storm Sanitary Analysis?

Civil 3D is a software application that operates on the AutoCAD platform to optimize project workflows. It does this using smart objects, like dynamically linked models. B&N uses this software in detailed design to deliver road, sewer, watermain, site grading and other projects. For stormwater system analysis, we use this application to define the elements of a stormwater system – sewer networks, catchments, flow paths, surfaces or stage-storage curves – as smart, dynamically-linked objects which can easily be migrated to SSA.

SSA is Autodesk’s powerful hydrology and hydraulic analysis application, which allows users to generate rainfall and runoff and model flows through storm or sanitary facilities using all the common model types, such as Rational, TR-20, SWMM or HEC-1.

Use These Tools for Stormwater System Analysis

On their own, each software can assess existing drainage systems or plan and design future ones. However, they are more powerful when integrated with each other and provide B&N with a system to relieve communities of stormwater issues. Here is the approach our team uses to employ Civil 3D and SSA to identify and solve stormwater issues:

1. Build It

To create a model, a Civil 3D pipe network is built to represent the existing piping and structures. This information is usually captured from field survey or verified GIS. Then, smart objects are defined in Civil 3D, such as catchments and associated flow paths. These smart objects can be assigned to pipe network structures. Lastly, the pipe network and associated catchments are migrated from Civil 3D to SSA. 

During the migration, we use data collected by the field services team to assign accurate rainfall data rather than using the default. With this information, the model is fully functional in SSA, where the smart objects defined in Civil 3D can now generate runoff levels specific to our client.

2. Calibrate It

Once the model is built, calculated flows are compared to actual flows that our field team measures with flow meters. We adjust the model parameters until they match the measured values to ensure the model is accurate. This iterative calibration process makes the model more accurate and useful for clients.

3. Corroborate It

There are several ways to corroborate the results. One strategy our team used recently was a public survey. The survey’s goal was to determine the current level of service (LOS) and identify deficiencies. For example, if residents couldn’t drive down a road in a rainstorm, then there was a poor LOS. 

The survey clarified where residents saw flooding occur, if there was water in basement, if they had a sump pump and more. In this case, the survey responses matched the output of our model and further validated the model results. 

4. Communicate It - With Civil 3D & SSA Output Tools

Civil 3D and SSA are not only design and modeling platforms but also powerful communication platforms. Our design or analysis can be displayed in numerous ways from a simple table to intuitive visuals that our clients can use to quickly understand results. An example of this output from Civil 3D is the Elevation Heat Map shown below. With the knowledge that purple indicates high elevation, and warmer colors lower elevation, a casual user can easily and quickly see the drainage pattern of the area, including the ridgeline on Redington Road from which water drains to the north and the south. 

Civil 3D elevation heat map of a surface created using LiDAR data

Below is another example of visual reporting generated by SSA. It shows an entire storm sewer system for an outfall with a background aerial. The pipes are color coded to represent the ratio between the peak flow and the full flow within a pipe, and anything in red indicates a surcharged pipe. The blue dots over structures represent areas where the water in the sewer tops their grates due to insufficient sewer capacity. In this figure, it is easy to see where this system is deficient along Green Meadow Drive. 

Visual representation of model results generated by SSA

5. Design It

After determining the deficiencies in the system, we suggest improvements. We build these improvements in the CAD environment, integrate them into the model, and study their impacts. The interoperability between the Civil 3D and SSA environments, along with the ability to merge models in SSA, makes the impacts easy to understand and allows us to explore multiple alternatives with ease.  

6. Apply It: Stormwater Solutions for the City of Newark

The City of Newark, Ohio, was faced with flooding in yards and roadways during storm events due to undersized or limited storm sewers, ponds and ditches. The City wanted to update its stormwater master plan to protect private property while creating better conditions for future development. 

B&N leveraged the functionality of the Civil 3D and SSA, along with our field services team, to update the City’s Stormwater Master Plan in the Cherry Valley Study Area. This master plan consisted of creating 3D networks of the storm sewer systems, modeling those systems, devising and testing solutions and collating this data into a comprehensive report. Additionally, B&N exported the data gathered throughout the report to shape files so that the City could easily update their GIS in the project area. 

B&N’s proposed solutions included installing a new storm trunk along a roadway that was also under design at that time. The City plans to install the proposed storm trunk simultaneously with the new roadway, leading to significant cost savings. The new storm trunk will relieve the undersized sewer in that area by redirecting flow from a low LOS-area and restoring it to a more natural drainage pattern.  

Additionally, B&N suggested that the City rebuild a road and sewer system upstream of the storm trunk, including adding a gutter and curb. This added value to the project while paving the way for additional economic development in the area.

B&N’s integration of Civil 3D and SSA applications allows us to accurately and efficiently identify stormwater issues. Our process allows us to design solutions and communicate their impacts clearly to our clients, so they can better understand how the recommendations can improve their communities. 

Contact me to learn more about our stormwater analysis and planning services.

Michael Spielberg, PE, Project Engineer

Michael Spielberg, PE 
Project Engineer