Tale of Two Springs (Earthcache) EarthCache

To log this earthcache, message or e-mail answers to the following questions to the cache owner to authenticate your online log. Do not post the answers online.

You will require a stopwatch or stopwatch app on your phone, or you can google stopwatch, for a stopwatch web site.

You will also require a container with a known volume, I suggest a 500ml water bottle.

What Is a Natural Spring?

When the empty spaces (pore spaces) in shallow subsurface rocks and fractures become saturated with water, aquifers or subsurface water reservoirs are formed underground. These water-saturated subsurface regions can extend very large distances and travel through the rocks using connected pore spaces. From time to time, the water inside these aquifers finds a way to the surface and seeps out to accumulate in different forms. The continuous feeding of the surface water by the seeping of a shallow ground water reservoir or aquifer is called a natural spring. Springs and their associated body of water types are fed or sourced by underground shallow reservoirs (Figure 1).

Figure 1: A natural spring formed by groundwater seeping above the surface

How Are Springs Formed?

When it rains or snows, the water seeps into the soil and finds its way into the pore spaces in shallow subsurface rocks below the water table. These rocks which are saturated by water are called aquifers or reservoirs. Reservoirs that have faults or fractures can hold even more water. The water inside the aquifer moves through rocks using connected pore spaces. In some instances, due to the geological characteristics such as presence of fault and fractures or stratigraphical leakage points on the ground surface, aquifer water seeps or leaks to the surface and forms springs. These springs can source and form various surface water bodies such as lakes and rivers.

According to the geological characteristics of the rocks associated with the underground water reservoirs, aquifers can be classified in two different types (Figure 2).

Unconfined aquifers: The water seeps through the soil and accumulates below the water table and forms the aquifer. If the geological unit above the water table is permeable, the water in the aquifer is unconfined and can easily move upwards through the rocks until it meets an exit point and forms spring.

Confined aquifers: The accumulated water inside the aquifer cannot move upward and is confined because there is an impermeable geological layer above the aquifer. In these aquifers, water travels laterally inside the reservoir until it finds an exit point where the impermeable layer ends or other types of geological features allow the water to exit.

Types of Water Springs

There are five types of springs. These are:

1. Gravity springs: When the surface water seeps down through geological units, the water travels until a barrier which is an impermeable unit. This geological barrier stops underground water from moving downward. Inside the saturated unit, water travels through the connected pore spaces by the help of the gravity until it encounters a topographical depression or exit point, at which point it seeps out to form a natural spring.

2. Artesian springs: In this type of spring, impermeable units confine the aquifer. In order for the water to exit or seep from the reservoir, there must be gaps in the upper impermeable units. This type of topography can be seen in valleys and cliffs. Because the pressure inside the aquifer is higher than the atmospheric pressure, the water is forced out of the gaps and contributes to either lakes or river systems.

3. Seepage springs: There are variety of factors affecting the characteristics of underground water flow such as pressure, topography, and types of geological unit. Seepage springs are observed in unconfined reservoir units which have good and connected of pore spaces. The water flows constantly and slowly in these spring types and generally finds a leakage point in topographical depressions such as valleys.

4. Tubular springs: The nature of the aquifer water and its movability mainly depend on the type of geological unit which makes up the reservoir. One of the extreme reservoirs is the large hollow underground spaces such as cavern and lava tubes. Both of these geological features depend on the specific rock unit as well as its properties. The dissolution of limestone causes the formation of underground caves and caverns. The lava tubes are the underground channels for the hot magma to move. These large extreme empty spaces can hold and transfer millions of gallons of water.

5. Fissure springs: In many cases, underground aquifer water seeps to the surface through topographical features such as depressions, cliffs, or valleys. This is the case in both unconfined and confined aquifers. Likewise, fault and fractures — in simple terms, cracks in the reservoir rock — can act as a vertical conduit for the underground water to move from subsurface to surface.

Spring Water Sizes

Spring discharge (or flow rate) is determined by the spring's recharge basin. Factors that affect how quickly a basin will recharge include: the size of the area in which groundwater is captured, the amount of precipitation, the size of capture points, and the size of the spring outlet. Water may leak into the underground system from many sources including pervious earth, sinkholes, and losing streams (streams which actually disappear into the ground).

Springs are often classified by the volume of the water they discharge. The largest springs are called "first-magnitude," defined as springs that discharge water at a rate of at least 2800 liters or 100 cubic feet (2.8 m3) of water per second. The scale for determining spring flow is as follows:

Questions to Be Answered?

At Stage 1

1. You will see a pipe coming out of the ground. Estimate of the rate at which the well is producing (in liters per second or milliliters per second). This can be done by bringing a container of a known volume along with you and then timing how long it takes to fill that container.
2. Based on your measured flow rate, what Magnitude classification number would the Spring fall into?
3. The Pipe is coming out of a hill, Estimate the height of the hill from the trail.
4. Where does the water go after it comes out of the pipe?

At Stage 2

5. Water is by-passing it So at the mini waterfall, estimate the rate at which the well is producing (in liters per second or milliliters per second).
6. Based on your measured flow rate, what Magnitude classification number would the Spring fall into?
7. The Pipe is coming out of a hill, Estimate the height of the hill from the trail.
8. Where does the water go after it comes out of the pipe?
9. Which stage has the faster waterflow?
10. What Type of springs are these, and why do you think so?
11. Pictures are not required, but  always  a great addition  to your log