Questions_Grading shrub bed & replace sidewalk (technical)

[oldgrowth]

For storm drainage purposes, not sure how many here have technical experience w/ grading (slope) of *shrub bed, (some of) *nearby lawn AND replacing a *sidewalk w/ proper slope.
(Sorry for long post. This is a complicated issue w/ several connected factors).

The shrub bed, lawn & walk all interact for drainage, starting at small, concrete porch.
Porch is in an "L-shaped" corner, formed by:
house front wall, & attached garage (gar. extends past house).

Any suggestions of technical forums or sites that may deal w/ grading yards / shrub beds, installing (replacing) a walk - focused on drainage?

Can post pics, elevation sketches - but multiple factors make it complex.

Biggest unknown is, what slope for sidewalk (where it acts as drainage) is "enough?"
*Standard engineering guidelines for grading (anything) next to slabs is,
1/4" / ft slope (2%) for FIRST 10 ft away from slab.
(problem I'm facing, after 10 ft, guidelines seem less clear).
Problems:
A 1/4" / ft slope for 1st 10 ft is doable on the walk.
It's the "acceptable" slope of last 18 ft vs. what's physically possible that may be a problem

1.The shrub bed lawn near it) are too high vs. slab ht (or 'brick ledge' ht.)
2.5" below brk ldg in some places
It's level w/ the small, concrete frt porch & sidewalk - where meets porch.
** Much of yard is higher than walk & (part) drains onto walk (length of walk). Trees prevent lowering whole yard (I'd like to).

2.Porch (fixed ht) - only 2.5" below brk ldg. Guessing not enough.
*Slab is uneven. "Hills & valleys" in surface.

*Porch or shrub bed may be 4", **OR 3" (or less) below *slab* (can't tell). Too little for 3" - 5" / hr storm.
Either way, not close to gov't / engineering guidelines for slab ht. above finished yard, walks, patios.
Slope of shrub bed / lawn isn't near recommended 1/4" / ft for 1st 10' out from a house ( unlikely could be).

Neither is my back yd, next to house, but drainage "path" across back yard & down both sides is considerably wider than the path of sidewalk by porch (even if a ~ 24" wide strip of lawn is lowered to new walk's level - length of walk).

3.The walk is MAIN drainage from this corner - (part of) main & garage roofs + a roof valley dumps here.

4.Shrub bed (or lawn by bed) can't be lowered much w/o lowering the walk, beginning at porch (replacing walk).

5.***Have only 5.5" drop in 28 ft from porch to walk's end, now.
approx. 1/5" / ft slope over 28 ft.
*If lower the upper walk - below porch level - & don't also lower the end of walk, it reduces the walk's slope.

To lower the end of walk (by 3/4" - 1.5"), have to make a 'swale' in yard, from end of walk.
Problem: Near this “new swale” is driveway on one side - a nice oak on other.
Taking 3/4" off part of root zone may be OK, but 1.5" is different.

New sod (the soil) ~ 1/2" - 5/8" thick, must remove that added amount from new swale, so final ht is right, after install sod (ask how I know).
Likely OVER 3/4" would have to be removed from -some- part of tree root zone. Don't like it.
Have to check how far a new "swale" would have to extend;- a few ft, or across 1/2 of tree's root zone?

 

[oneeye]

P

For storm drainage purposes, not sure how many here have technical experience w/ grading (slope) of *shrub bed, (some of) *nearby lawn AND replacing a *sidewalk w/ proper slope.
(Sorry for long post. This is a complicated issue w/ several connected factors).

The shrub bed, lawn & walk all interact for drainage, starting at small, concrete porch.
Porch is in an "L-shaped" corner, formed by:
house front wall, & attached garage (gar. extends past house).

Any suggestions of technical forums or sites that may deal w/ grading yards / shrub beds, installing (replacing) a walk - focused on drainage?

Can post pics, elevation sketches - but multiple factors make it complex.

Biggest unknown is, what slope for sidewalk (where it acts as drainage) is "enough?"
*Standard engineering guidelines for grading (anything) next to slabs is,
1/4" / ft slope (2%) for FIRST 10 ft away from slab.
(problem I'm facing, after 10 ft, guidelines seem less clear).
Problems:
A 1/4" / ft slope for 1st 10 ft is doable on the walk.
It's the "acceptable" slope of last 18 ft vs. what's physically possible that may be a problem

1.The shrub bed lawn near it) are too high vs. slab ht (or 'brick ledge' ht.)
2.5" below brk ldg in some places
It's level w/ the small, concrete frt porch & sidewalk - where meets porch.
** Much of yard is higher than walk & (part) drains onto walk (length of walk). Trees prevent lowering whole yard (I'd like to).

2.Porch (fixed ht) - only 2.5" below brk ldg. Guessing not enough.
*Slab is uneven. "Hills & valleys" in surface.

*Porch or shrub bed may be 4", **OR 3" (or less) below *slab* (can't tell). Too little for 3" - 5" / hr storm.
Either way, not close to gov't / engineering guidelines for slab ht. above finished yard, walks, patios.
Slope of shrub bed / lawn isn't near recommended 1/4" / ft for 1st 10' out from a house ( unlikely could be).

Neither is my back yd, next to house, but drainage "path" across back yard & down both sides is considerably wider than the path of sidewalk by porch (even if a ~ 24" wide strip of lawn is lowered to new walk's level - length of walk).

3.The walk is MAIN drainage from this corner - (part of) main & garage roofs + a roof valley dumps here.

4.Shrub bed (or lawn by bed) can't be lowered much w/o lowering the walk, beginning at porch (replacing walk).

5.***Have only 5.5" drop in 28 ft from porch to walk's end, now.
approx. 1/5" / ft slope over 28 ft.
*If lower the upper walk - below porch level - & don't also lower the end of walk, it reduces the walk's slope.

To lower the end of walk (by 3/4" - 1.5"), have to make a 'swale' in yard, from end of walk.
Problem: Near this “new swale” is driveway on one side - a nice oak on other.
Taking 3/4" off part of root zone may be OK, but 1.5" is different.

New sod (the soil) ~ 1/2" - 5/8" thick, must remove that added amount from new swale, so final ht is right, after install sod (ask how I know).
Likely OVER 3/4" would have to be removed from -some- part of tree root zone. Don't like it.
Have to check how far a new "swale" would have to extend;- a few ft, or across 1/2 of tree's root zone?

Hello friend, sounds like you have a big job to do. I wished I was there so you could show what you are talking about. Can you post some photos so we can get a better idea what you are working with?

 

[oldgrowth]

Thx. Can post pics. Raining.
Biggest? question IS,
* for sidewalk - part of a "drainage system" - away from a slab, if the *1st 10 ft* slopes 1/4" / ft, what's an acceptable "least slope" for rest of walk's length, in 3" - 5" / hr rain? (here, last 18 ft)

*Is it 1/8", 1/16" / ft? Or, "any positive slope after the 1st 10 ft should be OK"??

W/O *maybe* cutting substantial roots of an oak, to make a swale, have a LIMITED amt of drop available from porch to end of walk.
If slope isn't enough to drain BIG rains (3 - 5" / hr), probably floods house. It's that simple.

Pics may? not tell all.

Above: 1. frt porch only 2.5" below brk ldg. (On some houses, 2.5" below brk ldg = 4" below slab. Not a given on this house.
2. walk clearly lifted (~1") by tree (now removed). Lifted @ frt porch & for ~ 10 ft (still some pos. slope).
It's why walk must be replaced.
3. Re-pouring walk_ level w/ porch, may be partial? solution (not best, IMO).

4. Shrub bed soil (see thin mulch)_ approx. level w/ porch; also 2.5" below brk ldg (not good_heavy rains).
5. **Can only lower the shrub bed (enough below brk ldg to help), if sidewalk is also lowered _starting @ porch.
*Lowering shrub bed much below (any) walk level would block drainage.

**Emphasis is on big 2.5+" - 5" per hr rain storms, not avg T-storms. As is, will handle avg storms.
*Re-pouring walk_if only level w/ porch, improving the slope_SOME (of now lifted walk), will help.
But... leaving shrub bed @ current level + new walk_if level w/ porch & bed, may not be enough.

1. General, shrub bed_some spots_lower than - or level with - some of yard.
*Some of yard slopes toward shrub bed; bit farther from house, starts sloping to either the walk, or (west) side of yard (where swale is) . Yes, builder was idiot not to grade whole yard away from house (some).

2. Note the replaced, lowered sod strip along (uplifted) walk. This can / will be lowered more, after replace walk.
**Making this strip *over* 2 ft wide (good idea) means cutting lots of oak roots, on near 1/2 the root zone.
3. The walk's slope + lowered sod strip by walk + narrow bed (R of walk), make the total "drainage path" from the corner.

4. General, slope of all these are set by the *new walk's slope. Shrub bed drainage set a lot by height of walk.
**W/O lowering shrub bed & nearby lawn (bit more below slab), requiring lowering the walk @ porch , the "drain path" capacity of may not move water faster than it runs to this corner, in big storms.

Above: Red oak to protect. Note roof valley over sidewalk, near porch & end of shrub bed.
General, yard's center is higher. E. side (L of walk) slopes to walk. (Yes, Walk is tilted). On N. side of oak (toward house), yd slopes to house.
Has a Crown in ctr of yd_some rain runs off to each side_not ALL to house.
**Red oak_ ~ 9 ft left of walk_ ~ 12 ft from shrub bed.
*Grading much of the yard_in front of shrub bed, OR more than ~ 2 ft to left of walk (either area, all at once), may kill it (hot south). Seen it often.
Grading / lowering soil (near tree) in small sections_per yr_may spare it (take YRS to complete).

Above: from walk, looking W; yard slope slightly to shrub bed; Crown in middle curves both E & W.
Red oak just out of frame, to L.
**NOW, the drainage of this part of yd_in pic_depends a lot on the crown, curving to & away from camera.
Shrub bed also drains E or W, parallel to house, not "out from house." I'm 'mazed this corner's never flooded the house_it will.

Both drain either to the walk or W. side (that has swale).
Existing (in pic) is OK for "avg" T-storms, but brings some water closer TO house in big storms (not away).
In BIG storms, it adds water in the corner area.

*As see, if shrub bed by slab is lowered by 1.5" - 2.5", then yard, even 4 ft outside the bed would be lowered 4" or more.
!!! Regrading bed + lawn strip in front of it, need SOME slope away from house (or much of huge effort is wasted).
**Sloping regraded area out from house means removing many inches of soil from lawn strip in frt of bed.
Ignoring tree root damage, if do that, then seems a "mini retaining wall" is needed where old, higher yard meets new, lowered yard.
Ugh, this never ends.