Case Study: Hydrology and Geomorphology

Arizona Firm Models Projects More Accurately, in Less Time with RiverNET

Background Information

In the desert southwest, rain comes infrequently. But when it does, it’s often fast and heavy. Combine that with steep mountains, narrow ravines and wash beds that have been turned into paved roads and the result can be powerful and dangerous.

Hydrology and Geomorphology, with offices in Tempe, Tucson, Phoenix and Flagstaff, Arizona, specializes in engineering services to address desert challenges: floodplain delineations, erosion hazard analyses, sediment transport studies, watercourse master plans, impact fee analyses, drainage cost assessments, riparian boundary determinations, and navigability studies.

“In our area, we have lots of dry riverbeds, various types of channels and foothill washes. Each poses a different challenge,” said Jacob Rod, P.E., Project Manager.

As many Arizona cities have experienced rapid growth in recent years, public agencies, land developers, and engineering consulting firms have turned to them to help ensure that construction does not increase flood risks.

Automated Modeling

Pima County Regional Flood Control District, where Tucson is located, accepts only standard HEC-RAS and HEC-2 input and output data files. In the past, engineers performed this modeling manually, cutting cross-sections by hand and inputting the data into HEC-RAS and HEC-2.

“It was very cumbersome to accurately determine ground stationing and elevation data when cutting cross sections,” Rod said. “It required a lot of debugging and checking of work.”

From previous experience, Rod knew the efficiency of automating HEC-RAS and HEC-2 within AutoCAD. At another firm he had used RiverNET software from BOSS International, a sophisticated river modeling software that automates HEC-RAS and HEC-2 within AutoCAD.

With RiverNET, engineers can perform modeling tasks directly within AutoCAD, including bridges, culverts, spillways, levees, bridge scour, floodway delineations, flood plain reclamations, and stream diversions and realignments.

FEMA Flood Zone A Projects

The software’s ease of use allowed the firm to begin using it quickly on projects. “If you know how to open AutoCAD and cut a cross-section, you can use RiverNET. It’s that easy,” Rod said.

They combines electronic data from surveyors and topographic data from the county. Rod imports and exports data between RiverNET and HEC-RAS and HEC-2, as well as uses it with Civil 3D and ArcView. He turns to the software for a diverse range of projects, including floodplain analysis and studies, encroachment analysis, master-planned communities, LOMRs, CLOMRs, sheet flow areas and flooding in alluvial fans.

In particular, Rod finds RiverNET invaluable for streamlining and improving modeling for FEMA Flood Zone A developments. For example, on a large, master-planned community, the developer wanted to create drainage corridors to encourage north-to-south sheet flow.

With RiverNET, Rod modeled the drainage corridors and set encroachments inside the corridors to account for the fill. On the downstream side, he modeled how the flow is transported into the drainage corridor along the roadway embankment. In total, the project involved about eight to nine miles of HEC-RAS modeling across seven to eight corridors.

On a 12-acre commercial Zone A site, Rod remapped the floodplain and set encroachments to provide bank protection for the commercial paths in the development. He created a LOMR and used RiverNET to remap the floodplain and floodway, and make channel improvements.

AutoCAD Integration

Automated floodplain mapping within AutoCAD using RiverNET gives Rod flexibility in moving data back and forth between various programs, and in sharing results with clients.

“We can map floodplains directly within the AutoCAD environment, so topography is taken into account,” he said. “I don’t have to manually draw floodplain lines. I press one button, and there’s the floodplain map. With maybe a few minor tweaks to line styles, I have digital files ready to transfer to any map immediately.”

When Rod develops a drainage report for another consulting firm doing construction grading, he provides the file created in AutoCAD using RiverNET and the other firm drops it directly onto their drawing.

“Because it’s done in AutoCAD, files fit into anything you’re doing,” he added.

Cutting Modeling Time in Half

RiverNET reduces modeling time, enhances accuracy and gives them the maps and graphics necessary for presentations to clients, county review agencies and FEMA.

Rod estimates that the Zone A master-planned community project would have taken more than twice as much time without RiverNET. If he had to cut cross sections by hand every 200 feet, 1.5 weeks would have turned into four weeks instead. That allows them to deliver results to clients more quickly.

The software likewise contributes to better accuracy. “I have greater confidence because I can see everything instantly and know whether the map is accurate. When you’re doing this electronically, it eliminates human error,” he said.