DR9401-CS 931209 MEMORANDUM
To: Frank Trando, Interim City Manager
From: Kenneth M. Griffin, P.E., City Engineer ~
RE: Mr. Delvo's letter addressed to the Mayor 10/25/93
Date: December 9, 1993
I have reinvestigated the existing ditch that separates Devonshire Estates from Shadow Ridge
Estates. When Shadow Ridge was developed, a 20 foot easement was platted along the north
side and a ditch was constructed. The as-built construction plans show that a 4 foot wide
concrete flume was constructed in the bottom of the channel and that the side slopes were 4 to
1. This creates a gentle ditch section with a concrete base that could be reestablished if there
were any erosion or siltation. My investigation of the channel shows that the concrete was not
placed for the entire length of the channel and that the side slopes are steeper than 4 to 1.
/In September 1992, I wrote a memo to Alan Ratliff, City Manager, concerning this situation.
The memo was that a concrete channel be installed in the ditch section
recommendation
in
that
/ to help eliminate the erosion and to maintain a stable bottom. That recommendation was based
/ on the fact that the grade was too flat and that the channel was too shallow. The shallowness
[ of the channel is accentuated because at two points in the alley in Devonshire Estates, low points
~/were created to allow for the water to drain from the alley section to the channel.
After receiving Mr. Delvo's letter, I reinvestigated the existing channel section in regards to
whether or not an underground pipe system could be installed so the channel could be enclosed
and possibly fenced into Mr. Delvo's yard. This would eliminate the maintenance of the channel
and the drainage problem at the same time. Based on my calculations, an underground pipe
system can be installed in the existing channel. The resulting system would generally contain
the following items:
42" RCP 400 L.F.
30" RCP 491 L.F.
18" RCP 36 L.F.
31 5/16x51 1/8" Arch Pipe 246 L.F. (This is for areas that are still too shallow to
accommodate regular pipe. During a design that involved
an on the ground survey, there still might be an opportunity
to use regular pipe.)
Curb Inlets 3 each
Remove existing headwall 1 each
Connect existing 18" RCP 1 each
Retaining Wall 90 L.F.
Hydromulch 2600 S.Y.
Based on my initial calculations, the approximate cost of the above drainage improvements will
be $98,000.
Mr. Delvo also asked the following questions in his letter:
Q: "What ever happened to our concrete runway that was suppose to line the ditch
from end to end?"
A: I cannot answer this. I am also unsure why the as built plans show a "concrete runway"
when in fact to the best of my knowledge there is no concrete flume in the bottom of this
channel.
Q: "How much water enters the ditch from the flume?"
A: I assume he is referring to the flume that is directly behind his property. There is
approximately four cfs of water entering the channel from that flume. There are also
four other flumes discharging various amounts of water into the channel.
Q: "How much enters from the 18" RCP pipe?"
A: There is approximately 3 cfs that enters the channel via the 18" pipe. The 18" pipe was
utilized because that is the minimum diameter pipe allowed.
Q: "Also, what would be the minimum diameter pipe I would need to have the ditch
enclosed."
A: Based on previous conversations, I am assuming that he is speaking specifically of his
rear property. Based on my calculations, he would need a 30" RCP pipe at the rear of
his property.
The question that he does not ask is how much water is coming from the school immediately
west of his property. This is the area where the majority of the water going into the ditch comes
from. The school site is discharging approximately 16 1/2 cfs of water into the channel. For
Mr. Delvo's information, at the channel adjacent to his property there is approximately 3.9 acres
of land discharging approximately 21.4 cfs of water.
At this point, I am unsure how to handle this situation. Even though there is an engineering
solution to the problem, it is not one of the drainage priority projects in the Storm Water
Management Study. Also, there is currently no funding available to construct a project that
costs upwards of $100,000.
I would be happy to sit down and discuss this with yourself, the Mayor and/or Mr. Delvo.
At this point, I would like to request direction as to how you would like me to proceed with this
problem.