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You need to prove where your project ties into the existing condition model both upstream and downstream.

Yes, the different durations for a specific frequency are known as different design storms in the industry. What to choose? Depends on the typical storm makeup for your region and how large of a watershed area your are trying to accomodate. An intense convective 2hr storm may quickly overwhelm...

Implementing a routed hydrograph analysis to size an emergency overflow spillway can result in disaster. Spillways should be sized using non-routed peak flow (i.e. 100 yr peak) from the developed tributary area, plus any offsite flows that need to be conveyed through the pond.

If you are using SCS in an urban setting concerning detention volumes, make sure you use the weighted-volume approach and not area-weighting of CN as in TR-55.

Ok, I see it now. Thanks

No, that's not correct. Fig 2-4 is to be used when impervious is less than 30% Fig 2-3 is to be used when impervious is >= 30%http://files.engineering.com/getfile.aspx?folder=1545c2c4-18ce-4416-a045-f208e1d75ccc&file=Capture2.JPG

TR-55 states that the composite CN value for disconnected impervious greater than 30% should be computed from Figure 2-3. In the attached screen capture there is a 20ac site with 10ac unconnected pavement and 10ac pervious. HydroCAD is taking the weighted average to compute a composite CN of 69...

Thanks, my question is only about the latest state of the art for static (not RTK) GPS accuracy technology . I'm getting ready to interview surveyors for the project, and looking for some current background information based on true non-vendor experience with the latest static GPS technology.

You can model the infiltration trench/perf pipe setup in SWMM. Sounds like your design approach assumes the trench is clogged, but the surface grading design has enough capacity by itself to convey the design flows, therefore you would have a redundant and conservative design. Don't forget your...

This is for use in the civil world for the monitoring of structure movement. This is typically done by surveyors with levels.

No HydroCAD is not industry standard for modeling storm sewer systems requiring HGL/EGL analysis to examine backwater influences. The reviewer will want to see an HGL/EGL analysis for the 100yr event with a fully vetted 100 yr downstream boundary condition per their concerns (tailwater).

Yes, as a CAD designer alone you are not legally qualified to do this work by yourself.

I wanted to check in with the experts on the current state of static GPS equipment and technology. Is it possible to achieve standard deviation errors of position at 0.254mm horizontal and vertical accuracy for structural deformation monitoring with any of today's equipment? How about 1mm? If...

The "porosity" of the stone will quickly clog shortly after construction. Need to design an outlet that is maintainable.

Your most important design issue is designing the forebay water quality structure to meet its required detention time (12hr, 40hr) and drain in no more than 72 hours for the frequent water quality events. You can't do this with rocks.. you need an engineered outlet device placed within the rocks.

Sedimentation occurring in the pipe due to inhibited velocity and backwater. Sediment will drop out of the low velocity flow instead of being transported and passed through the culvert. If what you are saying is true, you should insist the riser obviously be removed and a proper flared end...

Extreme embarrassment, being made fun of, object of never ending ridicule.

For waterlines we put blue board over, but culverts are exposed to air and freeze.

No, the Modified Rational method is a hydrograph method used for sizing detention. StormCAD uses the traditional Rational Method, has been around a long time, and is widely accepted software. It is common to design for pressurized flow to save on cost, and is allowed by municipalities.

If it's in a Sag location, or moving an On-Grade inlet uphill, there's a chance the floor may rise above the existing pipe inverts.