part time amateur engineer

It's gonna depend on your sand somewhat. The sand at Naragansett Pier was measured in 1919 (This was the same year my son retired, so I remember well) and was found to be 1 in 14.

Do the experiment suggested by PW. Keep in mind you are always talking about sand in water. That is not the same as wet sand. BTW, I actually gave you the answer except for differences in sand (anyone who mixes their own mortar knows, for example, the difference between dredged river sand and seashore sand); principally, the angle will be increased by the presence of aggregate shells, gravel, etc. Note that my figure of 1 in 14 precludes any trenching without shoring. If you truly need an exact figure, contact the Army Corps of Engineers.

Oh BTW, I found data on Atlantic shelf sand in the sort of experiment PW proposed, except with no stirring. The limiting angle was found to be 12°. This was done in response to the cut slides encountered while digging the Panama Canal (It was in all the papers!).

Theory and reality often differ. Since, I'm sure, there are other canals in your area, some that may have been constructed by the Army Corps of Engineers, observe the work done on those, even if on a different scale. This will also give you some idea as to erosion over time, something that theory may not be able to address accurately. You may even find that a buffer of rock could prevent undermining / washout. Remember, there may not be aggressive flow but on a windy day, and I'm sure you will have some of those, wave action could wash away sand.

A system which I have seen used quite successfully is for the dredged sand to be filled ( by a trailing suction dredge ) into cylindrical synthetic fabric bags. The bags are carried under the small suction dredge and gently lowered on the bottom near the beach

These when filled are laid parralel to the foreshore . If required they are made into a pyramid shaped wall which contains the further filling (without fabric bags) of the sand needed to replace the eroded beach sand i.e between the beach front and the artificial under water " retaining wall ". Not too expensive and it definitely works.

P.S. If you do not have a dredge you can simulate one by building a simple sand pump. This can be made with an air compressor jetting air( and connected thereto) at the bottom of :6 ~ 9 inch pipe . This is held vertically on the area to be dredged. To this you should add a very good sludge pump (connected to the top of the pipe ) that will take the sand in suspension in the sea-water to where you want it delivered.

Labor Omnia Vincit.

Just be careful! Here are a couple of generalities:

• Canals have a clay liner made of puddle clay (this especially applies to the older canals). The sand/slime/mud is accumulated debris. When you dredge, be sure that you are not damaging the lining of the canal otherwise it will spring a leak and you will not have a canal anymore. Certain modern canals do have retaining walls and even retaining beds over certain parts of the canal. These are very expensive for a variety of reasons: cost of concrete, durability, adaptability to ground movements
• Are you talking about temporary stability or more permanent stability? Temporary stability is quite good and can be as much as 45 degrees prior to installing other material.

Hello again pwhagood

I had a further think about your dredging, and before you start, it is best to ensure there is no possibility you are above a natural limestone cavern.

If you break into one (Florida is renowned for sink-holes developing suddenly), then you, your canal, and your house, plus the neighbourhood may disappear down the hole.

Refer: http://www.floridaenvironment.com/programs/fe00619.htm

also (pay site): http://www.springerlink.com/content/80q662v302888516/

Kind Regards.....

This post brings to mind one interesting catastrophe:

http://en.wikipedia.org/wiki/Lake_Peigneur

Truly amazing!

While limestone maybe of some concern, I believe i would first consider the permitting process for dredging a waterway. Does it drain into a natural waterway? Is it waters of the US? Is there any potential adverse impacts to water quality or conveyances, threatened or endangered native species, cultural resources, transportation, business, or municipal/State/Federal facilities downstream. You should consult an expert before conducting such tasks, as there can be substantial fines from multiple agencies, and mitigations costs.

I would add that the local flood control authorities might be a bit miffed at you if you start dredging without getting the appropriate permits. Here in the Houston area, there is the additional issue of pollution. In some waterways, the silt has some nasty things entrained in it. The current thinking is that depending on what the nasty bit is, it may be better to leave the pollution in situ instead of trying to dredge it and stir it up, or at least to do the dredging a little at a time so that the concentration of the nasty stuff does not rise too high.

I live on a canal here in Florida and had same Idea until neighbor threatened to call slipmud the authorities in Florida governing all canals man made or otherwise so i called and was told that i needed a engineer to approve the dig and a certified contractor do the work.

big bucks any way what they don't know wont hurt them as long as you don't get caught be careful of sink hole in the area don't do it i used the county sink hole map on line to see if there were any close by none here TG i did use pump like above 3 in

pvc and pool hose to distribute muck behind break water made from 2x6 worked great as for neighbor a 2x6 pack of Bud did the trick

You'll want to use some caution. I don't know which county you are in, but here in Citrus County, ANY construction has to have plans stamped by a registered engineer, and all work done by a licensed contractor. (Well, OK, you can put up a tool shed of <250 ft² yourself, and a decorative fence < 4 ft tall, but not doors, screen windows, etc.) Plus, when it comes to water, SWFMUD (or its counterpart where you are) has authority over it even though it's "your" canal. Do not needlessly enrage the great faceless voice of authority, it has sharp teeth!

Having lived in So. FL most of my life, I've never heard anyone call it "my canal".

I don't think your local flood control district would appreciate you digging in their turf.

Sparky, the last few notes for your attention. But, if you are willing to plant crabgrass or any other plantlife anchoring the sand, you "may" get by with a 10degree angle. If you cannot secure that, maybe 5 -8 degrees. Exposed sand banks are not good idea, exposed ass to authorities neither.

At 90 Deg to Horizontal the sand can adequately witstand max 4.5-5% of mositure to the weight of sand mass involved.

Regards,

HEMANT CHAUHAN

Follow up question: How far down the sea wall can I dredge and not compromise the integrity of the wall? The wall slabs are 4" by 4' by 8' with a seawall cap. Very little current and no waves except by an occasional passing boat at idle.

without knowing the design of that specific wall, I doubt anyone can tell you with any authority. If there is a bentonite clay cap to prevent water percolating through, you have to be very careful. once that water barrier is breeched, that wall is coming down in the next storm. This is what happened in NOLA. The levee was designed and built using a misread soil report and the water percolated under and through the levee undermining it.

If you do this and the levee fails in the next storm, you had better hope you are killed, because if you aren't, the lawyers for your neighbors will do the job for you.

I cannot stress this enough. Leave the levee work to the professionals, and hope the soil report they have is clear and unambiguous.

Thanks for your reply. This is not a levee. The canal was manmade in the early 70's for a housing development. It has no flood control function. It mearly functions to provide recreational boating access to the back yards of homes. Most homes do not even have concrete seawalls but have pressure treated wood seawalls. The entire area is higher than the seawall. The canal is about 75 feet wide and about 5 feet deep in the middle at MLLW. I only need to move about ten cubic feet of sediment so that my boat lift can go low enough at low tide. I emphasize this only removing what has accumulated and not doing new excavation. THis sediment is from run off from the land. "Dredging" in these canals is a common occuring event. A "contractor " that has removed sediment from the canal before will be in the area next week, However the minimal is 30 cubic yards @$1800. Once again midcanal is ok its the area near the shore/seawall taht acummulates sediment from runoff and prop wash. Another contractor removes sediment using a trash pump. So once again my question is what slope will the sand in the water in this canal support? Just eyeballing the existing conditions next to my seawall it looks like a rise of 2 foot for every 3 foot of run. Thanks.

That slope sounds like the Contractor's Full Employment Act . Think about some kind of retainer (or the bags somebody suggested).

Remove only the sediment and "tile" in with cement bags the way the highway department protects the mouth of storm drains. That should support the wall, prevent undermining and washout and give you a baseline to dredge to in the future. At $3.00 a bag, that's about $1.50 a square foot by 6" deep for a relatively permanent fix.

And if you want to get fancy, stuff a lighting fixture into a bag or two and be the first one on the canal. That will also give you an indication when routine maintenance/dredging is needed.

"...stuff a lighting fixture into a bag or two and be the first one on the canal..."

Great idea! Waterproof fixtures, of course, but it would even make sense for making weigh or hauling out at night.

Low voltage or LED. With LED's there is the possibility of changing colors.

Oops! I'm beginning to think too much. This can only be trouble.