building a barn first curve ball

[dodge man]

Calculating the run off, rainfall amount, runoff coefficient are all pretty much simple and standard engineering practices. The same thing goes for modeling stream flows during a flood event, computer programs do it with all the inputs. What gets complicated is accurate topographic data on the stream and surrounding ground. If the topo map isn’t very good neither will the flood elevations. The truth is historic data is often the best from an old timer living in the area.

 

[Rockbadchild]

Calculating the run off, rainfall amount, runoff coefficient are all pretty much simple and standard engineering practices. The same thing goes for modeling stream flows during a flood event, computer programs do it with all the inputs. What gets complicated is accurate topographic data on the stream and surrounding ground. If the topo map isn’t very good neither will the flood elevations. The truth is historic data is often the best from an old timer living in the area.

I will challenges you on this I hope you don't mind.

The problem with historical data from a old timer is it's not a credible data for anyone other that persons, its purely anecdotal. I can't go to the town office and say this persons lived there for 80 years and he never got flooded therefore its impossible. One can be 100 year old and haven't seen a 100 year storm, never mind recording the data like antecedent precipitation or exacts water level and condition. Also things changes over time, like the forest got clear cut or they planted trees, next door farmer created drainages ditch's or they built a parking lot all these would affect his previous experience. I will stick to what I can prove and demonstrate on paper. My dad is the one who lived there the longest, we are talking about 3 house on that watershed and we are the lower so he would have the best knowledge but its is not provable or demonstrative and he only been there 40 years not 100.

Accurate topo data are the easiest it ever been to get nowadays with drone lidar survey although still can be expensive and time consuming over a large area.

I am sure you know but yes these two or three factors and coefficient are easy to find or calculate but if only these are used, but if used in a design it would result in a vast over design for an accurate calculation one would also need factor like soil abortion, overall watershead slope, roughness coefficients, and these over a large area can be hard to get right then one need to do it with three different antecedent condition variables, good, poor and bad and choose the risk you are willing to take.

 

[dodge man]

You’re right, some of the calculations are subjective. Before I retired I surveyed for a bridge replacement, I probably spent 3 or 4 weeks in the field surveying for it counting the boundary work. This was on a county road with a large stream rather than a river. It takes a lot of work for the flood calculations data in the field. I talked to the guy that had lived nearby and asked him how high the water had been, he was a long time resident. He pointed to a door sill on a garage and said the water had gotten to there. You correct, we can’t design a bridge based on him pointing to a door sill but it does help give us a lot of confidence in our calculations.

When they calculate a flood elevation we build a bridge above that number but not by much. I don’t know how much we build above it but it’s not like we build it 10 feet above the flood, maybe just a foot or two.

 

[Rockbadchild]

You’re right, some of the calculations are subjective. Before I retired I surveyed for a bridge replacement, I probably spent 3 or 4 weeks in the field surveying for it counting the boundary work. This was on a county road with a large stream rather than a river. It takes a lot of work for the flood calculations data in the field. I talked to the guy that had lived nearby and asked him how high the water had been, he was a long time resident. He pointed to a door sill on a garage and said the water had gotten to there. You correct, we can’t design a bridge based on him pointing to a door sill but it does help give us a lot of confidence in our calculations.

When they calculate a flood elevation we build a bridge above that number but not by much. I don’t know how much we build above it but it’s not like we build it 10 feet above the flood, maybe just a foot or two.

ha I see that make sense the old timer statement is to add credibility / confidences in your calculation and not as a replacement which I thought that's what you meant.

 

[dodge man]

Long time residents are actually a valuable resource. You can do all the math, calculations, computer simulations etc. but someone that saw it happen helps. The problem is what did they witness, a 100 year flood, a 25 year flood? Sometimes you can go back and find historical data on rainfall but you usually don’t bother.

Also what is a 100year flood? I live about 40 miles from the Mississippi River. I’m 61 years old and they’ve had three hundred year floods.

 

[Rockbadchild]

Long time residents are actually a valuable resource. You can do all the math, calculations, computer simulations etc. but someone that saw it happen helps. The problem is what did they witness, a 100 year flood, a 25 year flood? Sometimes you can go back and find historical data on rainfall but you usually don’t bother.

Also what is a 100year flood? I live about 40 miles from the Mississippi River. I’m 61 years old and they’ve had three hundred year floods.

yeah when I was in school they where talking about that lately the frequency of 100year flood is increasing and what number should they used when some storm exceed it, like in my case the storm precipitation I used in my calc was bigger then the 100 year storm which is odd if you had that big of a storm in the last 100 years should it be that number?

 

[paulsharvey]

I could be very mistaken; so want to say that first; But typically I thought you could build most places in a 100 year storm plain, but not in a 25 year?

Also, a 100 year event, is going to happen. in average, like every 50 years. A 10 year storm should average about every 5 years. A 100 year event is a 1% chance per year. I know that's not really how statistics work; it's not like once you reach 50 year, then you have a 50% chance, then a 51% chance; but in theory, you have roughly a 1% per year. A 25 year event; roughly 4% chance per year. One of the things that make it almost impossible to really design flood proof features; there is always the chance of a 25 year, followed immediately by a 100 year event. Or multiple minor saturating events; followed by a heavy event. Also, I dont know how frozen ground affects infiltration.

All of that disregards weather cycles; like La Nina, or El Nino, tropical storms, ect.

Guess what I'm saying; a barn in a 100 year plain, I wouldn't worry about; a 25 year plain; I would look at ways to raise the grade (if allowed).

A lot of drainage design is about minimizing catastrophic damage, but assuming some damage.

Note: not a drainage engineer; although I have listened to them speak to other engineers many times; most of the actual storm events, models, ect are over my head.

 

[Rockbadchild]

I could be very mistaken; so want to say that first; But typically I thought you could build most places in a 100 year storm plain, but not in a 25 year?

Also, a 100 year event, is going to happen. in average, like every 50 years. A 10 year storm should average about every 5 years. A 100 year event is a 1% chance per year. I know that's not really how statistics work; it's not like once you reach 50 year, then you have a 50% chance, then a 51% chance; but in theory, you have roughly a 1% per year. A 25 year event; roughly 4% chance per year. One of the things that make it almost impossible to really design flood proof features; there is always the chance of a 25 year, followed immediately by a 100 year event. Or multiple minor saturating events; followed by a heavy event. Also, I dont know how frozen ground affects infiltration.

All of that disregards weather cycles; like La Nina, or El Nino, tropical storms, ect.

Guess what I'm saying; a barn in a 100 year plain, I wouldn't worry about; a 25 year plain; I would look at ways to raise the grade (if allowed).

A lot of drainage design is about minimizing catastrophic damage, but assuming some damage.

Note: not a drainage engineer; although I have listened to them speak to other engineers many times; most of the actual storm events, models, ect are over my head.

that explanation makes sense

 

[Rockbadchild]

Slowly getting questions answered, my lawyer told me its not up to him to tell me if and where I can build on a propriety before purchases, which I find odd, like I buy a propriety with intention to built and he could let me purchases a propriety that I can't built on.... very strange. anyhow... also learn from the ministry that flood maps are only a tool to identify flood plains and municipality are entirely responsible for the mapping of them and its for the municipality to judge the best method to identify flood plains to minimize risk and hazard. So in other word they are the only responsible party and they did that map. I will stop sending emails to them now and will go there in persons and will put reason in this person in question.

 

[Rockbadchild]

so finally got a response from the city and their consultant, i would need a certified/ registered surveyor to confirm my work is empirical evidence but the only registered firm is 3h away and i doubt they will do it for cheep or even take my work for granted and slap their name on it …. i could sign a waver removing the city responsibility in that regard so I will just do that. It’s pretty frustrating that my data need to be verified but theirs doesn't.

 

[Rockbadchild]

I talk to a surveying firm and sure enough they won't/can't used any of my information and would need to do their own, but wouldn't necessarily need to come on site, they could simply used public record map and base it on that, which is a lot less then I have provided. He told me that someone from the city simply should be able to come on site and make a judgment call and started telling me about that city's should fired their over prices consultant for the bigger centers... I was like ya I am figuring this first hand... I will see his quote but will probably simply sign the waver despite the probability of affecting my future resale value.

 

[Rockbadchild]

would you guys sign that waver ? or pay what ever that quote is to get it changed ?

 

[CloverKnollFarms]

I suppose I could have it surveyed at any point. I could sign the waiver, build, and if I felt it worthwhile later, have it revised.

 

[paulsharvey]

Depends on the cost of the survey, and weather there is another build able area for the barn. On principle, yes, but if the survey is $5000, and there is another suitable location on the property, I probably would not.

I think I missed a part about the waiver; are you saying that you can sign a waiver, acknowledging the flood plain, and then proceed? If so, I would sign the waiver. Surveys arent cheap (we are talking a full topo, not propety corners) dealing with the government BS isn't cheap, and how much would a barn being in a flood plain really affect resale value?

 

[paulsharvey]

For the question of using your data; from the surveyors perspective, I wouldn't put My license (Registered Professional Land Surveyor, edit: im not saying im licensed, but if i was, i would not want to sign your work) on the line, using your data; much like engineers prefer to 'concur' rather than 'approve' another's work. I would Assume, if you sign the waiver, you won't be able to finance or insure the barn?

From the owners prospective; the waiver doesn't change the risk, and you would eb Hard pressed to get the city/county/whoever, to pay anything towards flood damage.

One hold up could be, if this 100% personal use, or is the barn part of a farming or other work related LLC or an asset of one?

 

[Rockbadchild]

Depends on the cost of the survey, and weather there is another build able area for the barn. On principle, yes, but if the survey is $5000, and there is another suitable location on the property, I probably would not.

No there is not another suitable location to built, there is a place where it is not in the ''flood zone'' but it is far away from services and it is 14 feet lower then my current ideal location so I am not building there. They will let me built where I want with the waver but then the land stay in the flood zone. That's the part I don't like but like CloverKnollFarms said I can always get that changes in the future.

edit: its not in the city ''flood zone'' but it is in a real flood zone. lol

 

[Rockbadchild]

For the question of using your data; from the surveyors perspective, I wouldn't put My license (Registered Professional Land Surveyor) on the line, using your data; much like engineers prefer to 'concur' rather than 'approve' another's work. I would Assume, if you sign the waiver, you won't be able to finance or insure the barn?

I don't blame them ether but the fact they will do the same work I did with the same data minus some it's kinda ironically funny... I don't know about the finance I hope its not the case I never heard any bank doing such research on a proprety to find that out, as for as the insurance I simply will remove flood damage from the policy.

 

[paulsharvey]

So, for survey work, figure approx $300/hour, for a 2 man survey team, plus office work on top of that; if the survey took 3 days, plus a day of geomatics work, your looking at a lot of money. Then, when presented to the City/County, if they have any comments that need addressed, that's additional hours you will need to pay for.

 

[Rockbadchild]

So, for survey work, figure approx $300/hour, for a 2 man survey team, plus office work on top of that; if the survey took 3 days, plus a day of geomatics work, your looking at a lot of money. Then, when presented to the City/County, if they have any comments that need addressed, that's additional hours you will need to pay for.

they said they wouldn't even come on site simply based it on the public topo map

 

[Rockbadchild]

For the question of using your data; from the surveyors perspective, I wouldn't put My license (Registered Professional Land Surveyor, edit: im not saying im licensed, but if i was, i would not want to sign your work) on the line, using your data; much like engineers prefer to 'concur' rather than 'approve' another's work. I would Assume, if you sign the waiver, you won't be able to finance or insure the barn?

From the owners prospective; the waiver doesn't change the risk, and you would eb Hard pressed to get the city/county/whoever, to pay anything towards flood damage.

One hold up could be, if this 100% personal use, or is the barn part of a farming or other work related LLC or an asset of one?

Thank you for this, and you where right, the bank was reluctant on saying whether or not they would loan me the money for a building built in a ''flood zone'' without flood insurance...


I played a old trick on them and it look like we have reach common ground... It dawn on me that the only one that knew the flood zone limits was me but my word is not empirical evidence as stated by them so I moved the propose location near the corner that was not within the limit, then they came back to me that I needed 12m ( 39.4ft) of minimum front yard and there is room to back it up without being in the flood zone so I gladly accepted so we ended up half way between my ideal location and the location that wouldn't be in the flood zone...