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Re: Freestone vs. Limestone
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pc, interesting pictures. But the top photo does not show an "aquifer." And I think this helps understand your prior statement saying freestones also emenate from springs, just not out of limestone formations.

But, I think there is another subtle difference between freestone springs and limestone springs and that is that in limestoners, the majority of water entering the stream proper is doing so from deep in the aquifer, whereas freestone spring sources are likely to be areas of moisture saturation much closer to the surface of the land, which itself warms and cools considerably depending upon atmospheric conditions. Deeper water sources will not vary that greatly as they are insulated from the earth's internal heat and the sun's warming rays.

Ultimately, alkalinity and pH measures will be your greatest clue to where the majority of the streams source water is coming from.

Posted on: 2011/12/6 9:30
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Re: Freestone vs. Limestone

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whereas freestone spring sources are likely to be areas of moisture saturation much closer to the surface of the land, which itself warms and cools considerably depending upon atmospheric conditions


You're correct up to this point. Even at only a few feet deep, the ground and water doesn't warm or cool significantly throughout the year. Freestone springs are indeed just as constant in temperature as limestone springs. AT THE SPRING itself, that is. Yeah, I've tested it. There might be a degree or two difference, I don't have enough data to prove that one way or the other. But within reason, springs can be considered to be constant in temperature. From freestone springs, I've gotten no lower than 52 degrees in February and no higher than 57 in August. Limestone springs vary similarly, maybe slightly less if at all.

But freestone springs are much smaller, and freestone streams start small and grow slowly. So at any given point, the % of water in a mature stream that is close to it's source spring is often quite low, and no springs are large enough to "rejuvenate" the stream. Add to that that in dry periods, many of the springs dry up or are reduced to a tiny trickle, and low flows also contribute to warming of the stream.

So yeah, it is accurate to say that some limestoners show a remarkable ability to maintain constant water temps, whereas almost no freestoners do once they get to be a decent size.

And yeah, it's also accurate to say that the best way to tell is with the water chemistry. Limestone is water permeable because it dissolves in water, hence the mineral content. pH is not a super reliable measure. Pretty much all limestoners will be on the basic side, but freestoners can be either basic or acidic, and they can vary greatly from one day to the next. Alkalinity is a very good measure.

Posted on: 2011/12/6 9:59


Re: Freestone vs. Limestone

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Spring water temperatures are constant in freestone areas as well as limestone springs. Springs in the north country in PA flow at 48F, even when the air temperature is over 90F.

Their water temps are actually colder than the limestone springs in central PA (50F), and southcentral PA (52F).

The difference is that the sandstone aquifers in the freestone stream areas in PA simply do not have as much storage capacity as the limestone aquifers.

So they do not have the capacity to soak up water during times when water is abundant (snow melt and rainfall), so they also have less water to release into the streams during dry periods. So, the freestone streams have flashier flow than the limestoners.

In low flow in the summer, the water coming out of springs and groundwater is still the constant temperature. But the difference is that there is little volume of flow.

On a hot day, a trickle of shallow water gets heated up more quickly by the warm air and sun, then a high volume flow. Just as if you put a little water in a saucepan on a stove, you can bring it to boiling temp very quickly. But if you put a big pot of water on the same burner on the stove, it takes much longer to heat up.


Posted on: 2011/12/6 10:04


Re: Freestone vs. Limestone

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Springs in the north country in PA flow at 48F, even when the air temperature is over 90F.

Their water temps are actually colder than the limestone springs in central PA (50F), and southcentral PA (52F).


Hmm, suspecting my thermometer reads a few degrees warm!!!! But very similar observations.


Posted on: 2011/12/6 10:11


Re: Freestone vs. Limestone

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Quote:

pcray1231 wrote:
Quote:
Springs in the north country in PA flow at 48F, even when the air temperature is over 90F.

Their water temps are actually colder than the limestone springs in central PA (50F), and southcentral PA (52F).


Hmm, suspecting my thermometer reads a few degrees warm!!!! But very similar observations.



It may vary a little depending on where you are in the "north country." Spring water temperatures are related to average annual air temperatures. So the further north and higher the elevation, the colder the spring water will be.

Posted on: 2011/12/6 10:27


Re: Freestone vs. Limestone

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This reflects a misunderstanding of freestoners, and I don't think it is true.


I actually did my doctoral research on flow in porous media, so I have a pretty good grasp of these systems.

I don't necessarily have a problem with saying that "nearly 100%" of the water in a stream like slate run comes from springs. However, it will be true that most of the springs will only contribute to surface flow if there has been significant rainfall within the last 1-2 months. Either way, you have a system that is dependent on recent rainfall to maintain flow. Many seep springs are basically nothing more than runoff from rain events that happens below the surface. They don't store a significant amount of water to put back into the system when it doesn't rain.

Limestone springs are very different. A component of the flows from these springs comes from water stored in limestone aquifers, and the residency times for water stored in these aquifers can be hundreds or even thousands of years. The contribution from the aquifer is essentially independent of rainfall, and these aquifers hold huge volumes of water. The output from most limestone springs also includes components due to conduit flow (ie. water that runs through sinkholes), which do dependent on recent rainfall. Residency times for water in the conduits can be as little as days or weeks.

When I say a "true spring creek", I mean a spring creek where a significant fraction of the water is coming directly from the aquifer as opposed to from other limestone conduits. These streams have very stable flows and temperatures, like the chalk streams of England or the cumberland valley limestones streams. The base output of the spring at Penns cave is 1-2 cfs. A big reason that Penns creek tends to get low without rain is that the springs that feed it are heavily dependent on conduits (and therefore rainfall) to maintain a high flow. The aquifer provides relatively little water directly to the stream. While this doesn't have a significant impact on the temperature or chemistry of the water leaving the spring, it has a big difference on the minimum flows in penns creek. This in turn has a big effect on the stream temperatures downstream because whenever the wide streambed isn't covered by water it warms up the creek a lot. Stable flows result in more stable temperatures because the surface to volume ratio is smaller at minimum flow.

We have a number of very large springs in Centre county. However, conduit flow and runoff play a very significant role in determining the flows of the central PA limestone creeks. I argue that this differentiates them from what I would call the "true spring creeks" of the cumberland valley or the chalkstreams in england. A higher fraction of the water in those streams is coming directly out of the aquifer, which is why they don't get as low as the streams in Central PA. The character of Penns creek is very different from a stream like the Letort or the Test. This isn't a knock on Penns creek, its just an explanation of why some limestone streams behave differently.


Posted on: 2011/12/6 10:30


Re: Freestone vs. Limestone

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Sounds reasonable, and more in depth than my explanation. Makes you kinda have to explain the various types of water and groundwater. Play with names if you want, just trying to understand/explain the concepts.

Runoff - Comes off of the surface after precipitation events, never enters the ground. Plays a part in both freestoner and limestoner alike, though, the longer the watershed, the longer this will take to exit the system. Temperature varies with the seasons and the surface it runs over (higher on pavement, etc.). Flows highly dependent on recent precipitation on the order of hours or days.

Freestone springwater - enters soil and loose rock, but not bedrock, as in my "freestoner" drawing. Comes out of springs, however, they are generally small springs. Temperature is consistent year round. Flow rate is dependent on precipitation trends on the order of weeks up to a month or so.

Conduit water - Like my "limestoner" drawing. Absorbs into soil, and penetrates bedrock, forming underground streams which emerge at limestone springs. Constant temperature year round, limestone chemistry. Flow rate varies on precipitation trends (several months).

Aquifer - Water that was absorbed by rock and released slowly. Various rock types absorb various amounts of water. Comes out in larger, generally limestone springs. Constant temperature year round, limestone chemistry. Flow rate highly independent of recent precipitation trends (maybe somewhat dependent on the order of decades or more).

Posted on: 2011/12/6 10:50


Re: Freestone vs. Limestone

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"Spring Creek is more classic and has a less diverse assortment of water types and critters. (Some of the lack of critter diversity is also due to pollution, but even in perfect health, it still would not display the diversity of Penn's and Fishing.)"

That statement is false. It's well known, and documented by Penn State reserachers, that Spring Creek had a great diversity of insect life, and pollution has wiped many of the species out.

There are still many people around who remember fishing the Green Drake hatch on Spring Creek. They were eliminated in the 1950s.

Spring Creek has a medium-gradient, and the substrate is cobble dominated. So it is very different than streams such as the Letort, Big Spring, and Falling Spring, which have a lower gradient, and finer substrate (gravel).

Limestone streams have a great variety of conditions. If you want to break them into two broad categories, you can use this break down.

I. Low gradient, fine substrate (typically gravel dominated)

II. Medium gradient, coarse substrate (typically cobble dominated)

But some streams have both types of waters, on different parts of the stream.

And both of these stream types are "normal", "typical" and "true."

In PA the mileage of the second category of limestone stream is probably greater than the first.

Posted on: 2011/12/6 10:59


Re: Freestone vs. Limestone

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2006/9/13 10:18
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There is a very direct connection between the flow in a freestone stream to the last rain event. That's one reason why they are as flashy as they are.. The base flow of freestone streams is very low because the sandstone aquafiers they eminate from hold only a fraction of the water a limestone aquafier holds.
Flows from limestone springs are well documented and have a fairly constant flow, but they DO vary in flow depending on rainfall, but rainfall has much less impact on the base flow inpart because the limestone itself is very pourous and holds much of the water that falls on the ground releasing it at the large springs.
Because sandstone ls hard and not pourous, most of the rainfall runs off. What water that is held in the aquafier is released slowly over a long period and the flow is very low.

Posted on: 2011/12/7 22:09
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It's time to stop stocking all wild trout streams no matter what Classification they are, and time to eradicate brown trout in some of our limestone streams and re-establish brookies in them.



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