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I have a question about ‘calibrating the model’ in HEC-HMS. I have pretty strong evidence that a storm of 1.8 inches produced no runoff in a desert gully in Eastern Washington. (State and county highway departments plus personal observation.) The 100 year storm is 3.2 inches. I believe...

I am dealing with a ravine that will experience runoff during a 100 year flood. Can installing a culvert and adding fill over the top be a justification for changing the flood zone designation? I am interested in hearing from people who have experience with FEMA in cases like this Thanks

I need to find the curve number for a couple of gravel parking lots. All I can find in the curve number tables of Hydrocad and TR-55 is gravel with right of way included. The numbers for that have to be lower than for just plain gravel pavement. I am guessing close to 98 but I don't want to...

Hi, Has anyone out there had any luck convincing NOAA that in certain cases their rainfall Atlas might be a bit too aggressive. We have a project that requires a 100 year storm. The value from the NOAA Atlas for the area in question says the 100 year 24 hour storm value is 3.2 inches. The 10...

Two problems with HEC-HMS 3.3 1. I change the units to US Customary and they just keep changing back to metric. Any way to stop this? I just loaded HEC-HMS 3.4. Apparently the manual did not get upgraded to the latest perversion. Items that were in the menu sytem in HEC-HMS 3.3 such as how...

Hi, I am working on a drainage project which has a large ravine running down the middle. The NRCS soil map classifies it as Te Terrace Escarpments. Every reference to Te I have found on the internet leaves all the characteristics such as available water capacity, depth to restrictive layer...

I have a project where there is a large bowl shaped area in the upper reaches. There are several dry gullies that would become intermittent streams in the event of a large storm. They all lead to the same culvert. Is it appropriate to model the entire area as a single catchment/sub basin or...

Neither HEC-HMS nor Hydrocad allow the runoff from a subbasin to be routed through a reach that is part of that basin. I have a situation where a small channel runs completely through a subbasin and the reality is that the runoff feeds directly into the channel every foot of the way. Since...

I am working on a report dealing with a bulging, leaky basement wall where a contractor used perf pipe instead of solid pipe to divert flow from roof downspouts. As a result the soil under the garage floor is so saturated that a second contractor drilled a hole in the floor and was able to push...

In "Civil Engineering Reference Manual" 6th Ed Michael R. Lindeburg P.E. on page 10-18 there is a section called "Horizontal Pressures From Saturated Sand". It gives an example of increased pressure behind a retaining wall. My question is, does this only apply to cohesionless soils or does...

Any suggestions on how to model open channel flow in a channel with zero slope and a drain located about halfway along its length? It is a unifomrly shaped asphalt channel. Thanks dpajr

I have a model with a single pond fed by two paved areas. The pond is prismatic with a bottom area of 6689 sf at an invert of -3.5 feet and a surface area of 8498 sf at an invert of -1.00 feet. By my hand calcs this should be a volume of 18,983 cubic feet. The runoff frm the two areas is 0.22...

I am trying to figure out how to determine the depth of flow across an asphalt parking lot (sheet flow or shallow concentrated runoff). I can calculate the accumulated runoff no problem but I am not sure how to get the max depth at any one instant. Thanks

I have a question about the use of settling jacks in a log home. One contractor is saying you need to adjust the jacks about every three months for the first few years. Another contractor says you can wait until the shrinkage of the logs is completed and then settle the jacks. Is waiting until...

Hi All, Does anyone know the soil type for EnF-Entiat. The NRCS map unit description says it is sandy loam with moderately high capacity to transmit water (0.57 to 1.98 in/hr). Which would make it Soil Group A. However, it also says "Available Water Capacity Very Low (about 1.8 inches)"...

I am working on a stormwater runoff project in a desert area. There are about 500 acres of mostly bare sandy desert. If I look up a curve number from a list nothing is an exact match but urban desert with CN = 63 looks close. However, when I use the "Available Water Capacity" from the NRCS...

I have a project of 500 acres. The terrain is very irregular. I divided the Basin into 7 subbasins. There are seven reaches all located in downstream subbasins. The upstream subbasins are connect directly to reaches located in a central basin which is surrounded by higher ground. Whenever I...

I did a stormwater runoff calculation on a ravine of about 500 acres in desert country using Hydrocad. FEMA rejected it because they say they are no longer evaluating any commercial software. That is frustrating because Hydrocad is such an intuitive program loaded with all kinds of helpful...

Hi all, I was stunned to receive a letter from FEMA saying that a project I had done in April using Hydrocad was unacceptable because they don't approve Hydrocad. It was especially surprising since Hydrocad uses TR-20 which IS one of the acceptable programs. My question is, of the various...

This is more of an opinion poll than a technical question. I am running Hydrocad 9. I am designing a retention system for a proposed public storage area. The soil type is Bf described as "Beverly gravelly fine silty sand". I used an infiltration rate of 0.3 inch per hour which is probably way...