stormwater analysis is a little complex but not because it's particularly
challenging but that there's just so many little steps along the way and once
you go to a different County they completely change how they do it but I
thought I'd go through a single stormwater analysis project in hopes of
highlighting where these differences exist but then walking you through how
it's done in one particular location so this particular project that I'm going
to show you is the conversion of an old abandoned car dealership into a
multi-family residential project we're going to be using in this project Google
Earth as you can see here and we'll utilize these tools to show us the
location of our project all the adjacent stormwater facilities the soil
conditions the precipitation maps and everything you can see here the project
is located at the corner of Foothill Boulevard and Bradford Street if you
click on the date' at the bottom left corner you can bring up past imagery so
this is what the site looked like when it was a fully fledged operational car
dealership as the credit crisis hit the car dealership was left abandoned for a
couple of years and then later plants came along from this particular
investment group to convert the car dealership into multi-family housing and
a commercial area construction on this site started around the beginning of
2013 and ultimately finished a year later in 2014 so this is our project
site to comply with local stormwater guidelines there were a number of
stormwater facilities planned for this project site on providing you in this
file the boundary line here that's all shown in blue is the boundary line I'm
also providing to you the proposed drainage facilities so if I go under the
file and I expand the folder out underneath under final project you'll be
able to see here the developed facilities if I check that box you'll
see the eight different surface inlets that convey stormwater runoff generated
on-site into pipelines that then convey the flow to the two highlighted yellow
stormwater BMPs those pipelines connect each of the
surface drains down to the BMPs before then they ultimately drain into the
storm drain located in Foothill Boulevard
so you see here drop Inlet 3 will get conveyed into a pipe which then
discharges into the BMP this area here the eastern area of the project five and
six and seven combined to a pipe that then drops into the stormwater best
management ello and same with inlet eight so I know I
said every stormwater analysis is different they do tend to follow some
general workflow for each project site and that's what I'm gonna go over with
you right now the general steps that you do on every stormwater analysis the
first big chunk of work that you do is basic research you want to create a
location map you want to know what other existing stormwater facilities there are
nearby you need to know what precipitation data there is for your
project site and of course the soils data for your project site once all of
that is gathered take a few moments and write up a summary about it it should be
pretty quick the second big chunk of tasks can be
done at the same time or in parallel as the first chunk and this is creating a
drainage map for the pre developed conditions writing a summary about it
and creating a drainage map for the developed conditions and writing a
summary about it so if you're working in a team these tasks can be divided up and
worked on in parallel and help complete the project much quicker the third chunk
of tasks is the hydrologic analysis for this work you'll build upon all of the
previous tasks and use that to find the time of concentration and create the
peak flow analysis calculation from the pre-developed and the
developed conditions and then do the first flush analysis followed by a
written summary of all of those results. The final chunk of work builds upon
everything that's been completed. It takes the hydrologic analysis that was
completed and applies that to the proposed facilities at your site. This
includes, for example, computing the depth and velocity of flow in each drainage
Swale on the surface, finding the the size of each Inlet, for example, the
curb inlets and the area drains; how big do those need to be? what size of pipe
needs to convey the flow from the inlets to the BMPs? how big does a BMP need to
be in terms of volume? And, of course, a BMP in this situation is a detention
basin so then what size of outlet do you need for the detention basins? and of
course, all along the way, write about your results. Don't wait till the very end
here, where you are trying to play catch up and being overwhelmed with the
writing. So my hope, with this series of videos, is to walk you through each one
of these steps giving you the confidence you need to do your own stormwater
analysis.