re: Back flooding and built up neighborhoods

Yea we used one of those models but like you said you need a lot of data. Ascension provided us with their entirety of GIS files from the past two decades, but that was just so much data we didn't even know what to do with it. Also contributing to the fact that none of really had too much of an idea much less training to develop that model we ended up i just had to modeling based on a recent development to "find" results in our alotted time.

All I'm saying is that, in my opinion, you may not be seeing any effects of new development in these areas. Most of them are likely close to BFE already and when you add new roads (including surfacing of old roads) and drainage issues that aren't being taken care of properly you could wrongly deduce that new developments are why you see these new flooding events.

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How are developers being allowed to do this?

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m

I’m sorry I thought this was America

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Do you know the status of the drainage infrastructure in these areas that "never flooded before"?

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I know the main waterway for our flood plain, the Amite River, has not been properly maintained. It was last dredged by the Feds in the 50s and left for the parishes to maintain. But none have.

The river itself has less of a capacity; thus the same rain today would cause a higher river level than a major rain Event 60 years ago.

To address the problem, I believe it needs to be done ftom big to little.

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Every development in the last 20 yrs has been required to dig out the dirt in the same area.

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they arent required to do that.....it is just more efficient to use the excavation material from your retention pond to build up the area you intend to build on.

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He is correct for Baton Rouge except that he underestimated the time. Other Parishes have similar requirements, just not sure on the exact time they were enacted. BR Flood ordinance was enacted in 1987. It required homes to be built above the flood plain and all developments to mitigate their 100 year flood plain fill among other things. Someone explained it earlier, for every unit of dirt placed in the flood plain, a unit of dirt must be removed from the same floodplain. That is accomplished through ponds generally. Only the volume between the normal water surface and the previous natural ground counts towards that volume. Anything below the normal pool level does not count since that is always full of water so it stores no flood water. The area above the water to the top bank is known as freeboard where your volume is calculated.

Generally, in the great flood of 2016, those houses built after 1987 where fine. There were a few outliers that were along the Amite, Comite and Hurricane Creek due to the fact that those basins experienced the full force of the 33" of rain and 500 year (0.2% chance) flood. Also, those house built pre-war time were also fine since they were built on high ground. Houses built between the 50's and 1987 were generally the ones that flooded. That is because those developments were not required to be built above the 100 year flood elevation, did not provide detention, did not provide fill mitigation and were built in flood plains. So actually, the older developments are the ones that have contributed to flooding.

Finally, the Sanctuary (Tiger Bend), The Willows (Burbank) and other new developments mentioned in this thread are not the cause of flooding.

I thought they updated the codes to say any fill dirt that is used to build up house’s or neighborhoods have to come from the plot of the neighborhood. That way it would mitigate the effects of building up the houses by giving the area a storm basin.

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How are developers being allowed to do this?

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No, I think there should be no new development in an area that flooded.

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I’m sorry, I thought this was a free country

How will any development including the Sanctuary cause flooding if 100 year fill mitigation is done? If the entire property held 50 units of flood water before development, then by ordinance it must hold 50 units of flood water after development. Since BR actually enforces that ordinance, how do you think flooding is increased by development? The issue is the general public does not understand hydrology/hydraulics and doesn't actually want to take the time to understand it.