A good start would be usgs WRI-87-4195 that is hard to find but available as a viewed file online. It has good hydrologic data based on geologic mapping and multiple wells in the Glenwood vicinity.
In terms of bedrock being disurbed by the water park as you were concerned about: The terrace alluvium and stream alluvium is 80-100 ft thick in the area where the proposed park will be constructed. This is based on well data on the south side of the river near the Amtrak depot (if there still is one there). The well at that site (just across from the Yampa spring) is collared in alluvium and goes through about 100 feet of alluvium and then into bedrock. Another well at the Roaring Fork confluence is completed in alluvium.
But here may be the problem: I recall something about artesian wells, I'm thinking some were actually in alluvial aquifers. The potentiometric head difference between alluvial aquifer and bedrock aquifer near Lodge is about 100' (higher in Leadville limestone). So there is this decoupled alluvial aquifer that may have some kind of carbonate seal, perhaps from precipitation of the carbonate and sulfate rich spring water. Maybe that's why there are some artesian wells that when drilled or pumped apparently have affect on discharge at other spring sites and in other wells.
This is all pretty gray as I've never worked there and just basing this on one pretty detailed report. But it sounds reasonable. If so, disturbing some kind of precipitate sealed alluvial aquifer could have impact on discharging hot springs nearby.
I don't think disturbance of the bedrock aquifer is the potential problem as postulated in your previous post.
Yes, good summary Andy. Thanks. It helps explain why the pool is concerned and why no study may satisfy them. If there is karsted limestone right under the river, we may be out of luck.
I'm confused by that the alluvium is 80+ ft thick near the train depot. Alluvium is nearly always very porous. 80+ feet is safely above the limestone and work in alluvium shouldn't effect the plumbing in the bedrock. Yet, the train depot is very close to the pool, where the alluvium is presumably much thinner, so it's not that simple. Yet, the pool and the pool building foundations go in the ground a ways--are they in alluvium?
Unfortunately, I'm fairly certain that geophysical studies won't be able to resolve the plumbing. Things are too heterogeneous and access is too spotty. The studies may be able to resolve the depth of the alluvium.
If there are wells drilled so close to the proposed play park, they should give the most reliable data of what is going on. Perhaps a few more can settle things.
In my last response to Andy, my details didn't elucidate the important point well enough. The hotsprings at Logde discharges in alluvium. No matter how much dredging is done in the river--well data and mapping indicates that ALL the dredging will be in river and terrace alluvium. Yes alluvium and gravels are basically porous. BUT...there is data that suggest that there is some aquifer in the alluvial layer AND it is somewhat separated but still has some plumbing connection to bedrock (limestone) aquifer.
The catch is that some well data suggests that the alluvium may not be typically porous, but may be locally or even broadly cement. Take a look at all the globby gray stuff on the margins of the hot springs pool. It's precipated from the sulfate and carbonate rich spring waters. This same stuff can also act as a cementing agent in the alluvial material as well. Thus there could be some kind of seal in the alluvial aquifer that could possibly be disturbed by dredging in the water park. What suggest this is that there are wells drilled (I think, but this can be verified) in the alluvial material what are "artesian"--i.e. they spout water above the top of the well or alluvium surface. They also impact water level in other wells.
From this data, it is suggestive that there really could be some kind of seal in the shallow alluvium. Again, this could be disturbed by shallow dredging.
Forget disturbance of the limestone bedrock. That is almost 100% likely not the issue.
We have seen a similar situation in a high alpine watershed, where iron cements the alluvial material. It kind of seals and forms a shallow "aquifer" so to speak. When a well is punched into it a river level it breaks the seal and up spouts and ...."artesian" well.
Replace the iron cement alluvium with carbonate cement and you could have the a similar scenario. Thus absoulely affecting discharge in springs nearby.
Please note this is still all hypothesis but based on some good detailed well logs.
The way you describe the system is pretty different than what I was thinking, but still has the same consequences for punching the bottom of the riverbed - break the seal and lose pressure in the artesian system. I can easily see how there could be a cement forming where the mineral water meets either the air or river water interface. Radically changing chemistry by either oxidation or mixing with the river water disrupts the equilibrium of the mineral water and the minerals precipitate, creating a cemented halo around the surface of the aquifer and sealing the alluvial aquifer so it becomes artesian due to the high pressure in the bedrock.
Thanks for setting me straight,
--Andy
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Good discussion geo-techies!! As a geological engineer, this is fun to read this on the 'buzz!
I want to propose an alternative solution to the problem. My disclaimer is that I still don't know all the specifics, just what I have read on here.
Instead of dredging down into the alluvium, how about GROUTING the alluvium in place and create a foundation for the park features. You could use down-stage grouting (starting at the surface and working down) with scattered injection points. In the process, you can get an idea if there is a confining layer of percipitated material (as discussed above). With this technique, you can create a very strong foundation without dredging. This also will cut-off additional water flowing through the alluvium and add flow over the feature. Additional grout that gets into the aquifer areas would have a "plugging" effect and not the broken pipe scenerio, which would increase aquifer water to other outlets in the system (hot springs pool).
Don't worry too much about grout travel in the river or aquifer. There are all kind of new admixtures that will allow you to control the flow, time of set, viscosity, etc, etc. Pretty cool technology out there.
One more thing. I recieved an email from a person regarding forwarding emails, I tried emailing you back, however for some reason it didnt go through. If you see this, Please feel free to call me(970-928-8702), For I don't think my email made it through. I would like to clear up some of the issues mentioned, and reassure you there is nothing to worry about!
I have always thought that the West Glenwood exit would be a better spot for the park anyway. Put in a ramp on the N.E. corner of the exit . Use the South Canyon exit for egress. More water, better gradient and do not add to the congestion of an already crowded boat ramp at Two Rivers. You could play in the park, slide down to the South Canyon wave, and soak in the hot springs in south Canyon post play. Maybe combine it with an extension of the bike path to South Canyon. Perfecto Amore!
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