Ground Subsidence

[moe333]

I am looking at a water-banking project and trying to evaluate if there would be subsidence due to the recharge and pumping operations over long periods of time.

Water will be "spread" on surface into a diked recharge basin of about one square mile. The water will recharge an aquifer with the current groundwater level at about 300 feet below surface. The "water spreading" will occur sporadically as excess water is available, and groundwater pumping will occur during times of relative drought.

The subsurface soils consist of sand/silty sand alluvium which probably grades from loose to dense with depth. I'm thinking there will be some ground subsidence as a result of the fluctuating groundwater levels, but I am not really sure how to evaluate what the magnitude may be.

Some adjacent structures such as well pads, pipelines, and weir structures could potentially be affected by the subsidence.

Any ideas on how to evaluate whether there would be significant subsidence, and approximate magnitudes?

 

[fattdad]

My gut tells me there will be insignificant subsidance.

Is this speculative banking (i.e., in the manner of wetland banking)?

f-d

¡papá gordo ain’t no madre flaca!

 

[moe333]

No, not involving wetlands

 

[fattdad]

Oh, I understand that this doesn't involve wetlands. I'm just saying after this project is complete, will you derive water-banking credits for sale in the open market?

Just wondering. . .

f-d

¡papá gordo ain’t no madre flaca!

 

[moe333]

I do not know the financial strategies for the water use.

 

[jheidt2543]

I would make two suggestions:

1. Assuming this is in the U.S., I would contact the U.S. Geological Service and discuss your subsistance questions with them. They have done a lot of research around the country on groundwater topics and may be helpful.

2. Contact some of the high capacity well drillers in your area, the ones that do city wells and agricultural irrigation wells. They may have some insight into ground subsistance on projects they have done.

One thing to look at is the lowering of the water table from your pumping operations; it could cause problems with private wells in the area. Our well pump had to be lowered some 20' when a nearby farmer installed an irrigation system that ran our well dry when he pumped.

 

[moe333]

Thanks for your suggestions, The water banking project will not lower the exisitng groundwater level, the recharge and pumping will cause the groundwater level fluctuations above the existing groundwater level.

 

[fattdad]

If you are geologically in an area with limestone, dolomite or other such calcareous parent rock AND if the region is prone to sinkhole development or the presence of caves, then you may have a relavent concern. Otherwise, I'd think there's not too much to worry about.

f-d

¡papá gordo ain’t no madre flaca!

 

[ecanuck]

Hello Moe333:

This strike me as a very interesting project. Is it done very often? I suppose it must be in which case there would be some peer information/assistance available.

I would say you have a legitimate concern about subsidence. A lot depends on the insitu conditions and you have not given much information. For sure if there is loose sand underlying you will get settlements and subsidence. Only settlements wold cause problems with the proposed construction since subsidence can usually be accommodated.

I would be pleased to comment more if you provide some details of the geotechnical conditions and proposed construction.

Regards,
Ecunuck