The surface water drainage ditch over flows it's banks 2

[frenchdrain]

Hello,
Any comments, would be greatly appreciated. My questions are;
Can this ditch be saved?

If the ditch can not be saved does any one have comments or suggestions?

The house is on a small lot with a 30" wide X about 24" deep surface water drainage ditch filled with drain rock along the back fence, it narrows to 24" wide X about 12" deep from the corner of the house to the street. In addition to needing a functioning drainage method for surface water, water from the downspouts are in a solid 3 inch pipe. The base of the fence is 2 1/2 feet above the floor of the patio, house, garage.


An aerial view is attached the letter "A" is on the roof. The 3 red spots represent the beginning of the ditch and where the 3 neighbors surface water enters the yard. The blue line is the path of the ditch taking the water from the back of the house to the street. At the beginning of the ditch and where it turns around the house soil was added to the base and sides to keep the grade consistent. Water seeps out of the ditch in these areas. At the corner of the house water over flows the banks of the ditch all the way to the street.


Thanks in advance,
FD

 

[frenchdrain]

Thanks for responding cvg,

Definitely, first the slope of the ditch must be reestablished. Only then would bentonite be something to consider.

As per July 12;
5. It doesn't matter what the upstream capacity is, you have a bottlenect at the bottom.

* Yes, the bottle neck is accessible to trenching equipment. It can be cleared of eroded soil and widened.

 

[beej67]

What sort of catch basins are out in the road?

If grading the ditch such that it's lower than the building footprint is impossible, you're asking for trouble down the line. I'm still not sure I fully understand your problem, but based on what I've read so far I would dig the ditch deeper than the building FFE, and continue with a positive slope towards the road, and if that meant that the ditch was lower than the road elevation at the curb then put in a beehive yard inlet and tie it to a catch basin somewhere in the road.

Positive drainage is absolutely how this gets fixed. Filling above your FFE to put a ditch in fill like some sort of back yard aqueduct is asking for trouble, because it will impede positive drainage of the back yard.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[frenchdrain]

Thanks for responding beej67,

I have attached the aerial view
source of the water/beginning of the ditch =3 red spots
path of the ditch= blue line



Sadly the ditch exists, the goal is to correct the situation before winter rains begin.

The house is on a city street, storm water from all the lots drain across the side walk into the gutter which carries it to the city storm drain. In this case the city storm drain is an estimated 400' away.

If I understand correctly keeping the ditch below the FFE the ditch at the sidewalk would be about 2' deep. At the city flood drain the pipe from the beehive yard inlet would be about 13' deep?


"I would dig the ditch deeper than the building FFE, and continue with a positive slope towards the road, and if that meant that the ditch was lower than the road elevation at the curb then put in a beehive yard inlet and tie it to a catch basin somewhere in the road."

 

[cvg]

if you are unwilling or unable to properly grade the ditch, then start floodproofing your house. A floodwall or berm (levee) might work. You can use the bentonite to waterproof that.

 

[beej67]

You've got 400 feet of road before the first storm drain inlet? Wow. The gutter spread implications boggle the mind. If you don't mind me asking, what state or country is this development in?

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[frenchdrain]

Thanks CVG! Great idea! Actually winter rain is the driving force behind getting a solution to this drainage issue.

 

[frenchdrain]

Thanks for asking beej67 this may be of benefit to others on his thread. The area is Sacramento county CA, with 23 inches average annual rain fall. This being July chances are slim there will be a 'real rain' before Nov.. The rainy season is from Dec to May or June, the heaviest being in Dec - Feb.

 

[frenchdrain]

Hello again,
First and foremost I want to thank all of you pros for sharing your expertise on this failed drainage ditch!


With that said, only through your guidance we have established the total area of the 4 lots draining onto the this lot is about 1 acre, and the acre is flat. The soil is heavy clay. The 159 foot fall from the back fence to the street is 4', the current slope of the ditch is 1/4" per foot. And last but not least the current ditch requires an extreme remodel/repair.

My question is; the maximum rain fall in this community is 1.6" in one hour (23" average annual rain fall) does any one have an idea what the minimum width and height of this ditch must be for it to function properly?
Thanks in advance. F G

 

[frenchdrain]

Hello, I forgot to add a disclaimer, I agree I will not at any time or in any way attempt to hold any one liable for the suggestions they have given on the repair or corrections of this drainage ditch.

The disclaimer was probably not necessary, but I really need to get this drainage situation corrected before winter rains and a ditch that is too small would be a huge setback.

Thanks again F D

 

[frenchdrain]

Hello again,
I had the good fortune to speak with a civil engineer with the city planning/building department, my ditch size questions have been answered.
Attached are pictures of the should I say, lack of progress?
The area next to the house was excavated to make room for the dirt from the ditch. The dirt from the ditch was used to slope the area from the ditch to the house some what like it was originally, but it is not compacted.

 

[beej67]

You guys got drainage manuals on the west coast? This is something that should be covered in either a county or state drainage manual.

Rational Method Crash Course

1) You'll want to determine your rainfall intensity from calculating (or assuming) a time of concentration for your basin (reasonable assumption for an acre is 5 minutes) and reading the intensity for your design storm off of an IDF curve.

2) Characterize the watershed's ability to absorb rainfall, by figuring a rational C coefficient. Either pick one off a chart or calculate it based on weighted averages.

3) Stick it in here:

http://www.lmnoeng.com/Hydrology/rational.htm

That gives you your flow rate in your ditch. Then use Manning's Equation to determine the flow depth of that flow, given ditch parameters.

4) here:

http://www.lmnoeng.com/manning.htm

I don't have any personal experience with those web calculators, but you might lean on them as a tool while you learn this stuff.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[frenchdrain]

WOW, Thanks beej67 !!

 

[Ryb01]

frenchdrain,

I've been following the correspondence within this thread for some time now. Seems like the older residential areas in regions with generous topography have similar drainage issues regardless of location.

Just out of interest, I wanted to ask you a couple of questions, as a number of things still are not adding up in my mind based on the previous correspondence.

1) In my past experience, drainage issues like these have required permits to be obtained prior to construction. Was there one obtained? What are the drainage regulations in your area? Some of the comments had touched briefly on this but I don't believe that there was a conclusion.

2)Is there an original grading plan for the subdivision? How does if accomodate the drainage from the other properties?

3) Seems like this ditch is a new concept. What was on this property to accomodate drainage before?

4) Is the flooding on the property a new issue or a past issue that needed to be dealt with? If this is a new issue, something has changed within the drainage area.

5) Is it necessary to fill the ditch with stone? Erosion protection on a residetial yard for 13cfs could be achieved with a permanent geotextile or even sod mats. This would obviously depend on a number of facotors(i.e. if using a trapezoidal section instead of rectangular, but an option to maintain aesthetics on the property.

6) A rectangular shaped channel, unless lined as cvg had outlined earlier, is not stable regardless of soil type. If grading restrictions permit you from shaping a trapezoidal shaped channel, is a shallow pipe system an option?

Again, just wanted to ask a few questions just out of general interest.

beej67, helpful link, thanks.

 

[frenchdrain]

Hello ryb01,
You are correct the house was built in 1976.

1. Current drainage regulations in this area, I haven't investigated, for this lot any storm water what ever the source is the owners problem. Permits, there is one on record for the house. It doesn't show where utilities connect to the house. There is no mention of drainage.

2.Original grading plan for the subdivision. 2 of the lots that drain on this lot 'mingle water', the farthest lot partially drains on to its neighbors dive way. The 'receiving drive way' has a cement drain leading to the common property line.

3.True the failed ditch is less than a month old. Prior storm water found its own way through the lot, the swamp grass is healthy.

4. The flooding is not new, all the houses on this side of the street have some flooding. This lot is the only pie shaped lot with the longest side connecting to 4 neighbors. thus more flooding than the rest.

5. Filling the ditch with stone and the rectangular shape was the designers idea. The ditch failed within minutes after a garden hose was running into it. Sadly a city official since recommended a 4 to 6 inch deep 'ditch' with shallow layer of crushed rock that will pack to prevent erosion, and sloping sides which accommodate a lawn mover.

6. Correct, the newly dug rectangular shaped channel is collapsing as cvg outlined earlier. Drainage pipe has been installed twice in the yard. A slotted pipe in a French drain in the side yard runs from the corner of the house to the street, it was apparently installed when these houses were built. Also in the last 10 or 15 years a solid pipe with inlets about every 10' was installed near the perimeter of the house and empties in the street on both sides of the house. Both pipes are fulled with clay. Pipe isn't very popular in this situation.

Any other questions?

 

[Ryb01]

Hi frendrain, thank you for Taking the time to reply. Was just trying to get a better feel for the project. As cvg and beej67 have indicated your best bet would be to probably create a defined channel in the alignment as you've shown on your plan. Some creative grading may be required. A trench filled with stone should mainly be used for infiltration purposes and not conveyance. The stone takes up a significant portion of the cross sectional area of the channel, thus resulting in a significantly reduced capacities.

Ho

 

[frenchdrain]

Thanks Ryb01,
Creative grading, interesting idea, any suggestions, pics or such to share?

 

[Ryb01]

Had a couple things in mind when I said "creative grading". The first thing that came to mind is, there has to be some give and take whith repsect to what is needed to control the flooded vs aesthetics on the property. Second is what is a higher priority for the homeowner? Prevent the house from being flooded or aesthetics of the property? or both?

There's an infinite number of solutions to rectify the flooding, cost is always the challenge.

The main goal for this property is to convey the external drainage to the ROW without flooding the house. Clearly a defined, unblocked, swale is needed to convey the flows. In doing this, the homeowner will essentially give up a portion of the backyard along the fence line and also around the perimeter of the house. As cvg had said earlier, berming would possibly andd more thank likely be required. You should be able to use the soil from the excavation of the ditch (if clay content) to construct the berming. With proper construction of the dith at a constant grade and proper compaction of the berm there would be no need for waterprroofing within the channel itself. As I had said earlier, sod may provide an adequate erosion protection for the ditch, obviously depending on the design of the ditch.

Regrading the back yard and installing a couple of pup catchbasins may also be required on the house side of the ditch. Usually thses catchbasins would drain to the storm sewer within the ROW. Seems odd that since the property is located on the corner of the street that there would not be some sort of infrastructure to tie into at this location. If the swale is sized properly, all external flows would be diverted around the house, only leaving the internal runoff from the yard to deal with (if any). The pup cathbasins could be connected to the sump pump and discharged to the surface at the front of the house. This would not be a significant amount of water and also not sure if local state plumbing regulations would permit this but it's maybe something to look into.

With the "creatiive grading" there may not be alot of room left on the lot. Looks like from the latest picture you posted that there's a decent grade within the back yard already and may become steeper with the installation of the ditch at the fence line. Another option would be to capture and pipe the flows, more expensive but still an option.


Hope this helps.

 

[frenchdrain]

Great ideas thanks Ryb01, adding a berm and making the swale as wide as the yard will allow seems to be the solution. The rain gutter down spouts across the back of the house drain into an existing pipe that has inlets picking up surface water hopefully it will take care of any 'other water'. The pipe travels around the opposite end of the house to the street. You mention using sod for erosion control, it would be very simple, however the plan is the yard will be drought tolerant. Any idea in this situation what plant or grass could substitute for sod?
Thanks in advance,
FD

 

[Ryb01]

Ultimately it all depends on what the homeowner is looking for.

You could keep the swale green, literally, by using a permanent erosion control blanket for erosion protection. I've seen blankets in green, soil, black and blue. However if the rest of the yard is not green this may look funny. If installed properly grass could still grow through the blanket and be cut with a lawnmower.

You could also use stone to line the swale. 6" would probably be overkill but depends on the final design of the swale.

If the home owner is looking for a natural look, could also plant/hydroseed fescue or other types of low maintenance grasses with a decent root base.

Again, it would depend on what the homeowner is looking for. The ideal solution would be to blend in with the yard and surrounding areas.

Hope this helps.

 

[frenchdrain]

Interesting ideas Ryb01,
The goal is a no mow yard, although there is concern the swale will erode without some plants and rocks to hold the soil.

The home owner is looking for a natural look, could fescue or other types of low maintenance grasses with a decent root base be used in a no mow setting with out looking like the house is abandoned?