Water in the desert

[MMM]

sal I am not sure what report you are refering to as far as OHV damage due to water crossings. In some areas, mostly back east, runoff from roads has caused some sedimentaion of streams and in this case, where justified, the roads must be paved, graded, graveled or in some cases closed. However, a few jeeps or OHVs crossing a desert stream causes minimual impacts on the stream. Most OHV/jeep owners do not like to go through water. Water is hard on equipment, seals, brakes, linkages and any number of other places where water can do damage. Also, streams hide nasty stuff like rocks and deep holes, so believe me, the last thing any reasonable OHV/jeep driver will do is race through any stream. Slow and easy in the water.

Any water falling on the ground (snow or rain) will either be absorbed into the ground or if the ground is of a nature that is highly impermeable (rock, sandstone, some kinds of shale, etc.) the water wil collect in bowels (vernal pools) (a critical environment for endangered species, like the farie shrimp and a host of other seasonal critters) where the water will, in time evapotate. These seasonal pools are generaly protected and must be avoided by al OHV drivers. But water introduces into the ground, may in time, refreash the aquifer. I say may because plant life absorbs large ammounts of water and is released back into the air as vapor. Water collectd into any basin, be it man made (OHV tracks etc.) will be absorbed into the ground, unless the ground is, once again mostly impermeable, in which case ruts and tracks will be few and far between. Aquifers are generaly recharged over long periods of time. The link you provided is accurate and true for GROUNDWATER. Aquifers generaly lie deeper than groundwater and are encountered by deep well drilling or deep mining. (Deep mines (those deeper than 500 feet) often require huge pumps to keep the workings dry and this is the reason many if not most of the old mines areflooded, they simply went deeper than the water table (the upper limit of a given aquifer).

sal writes "When we speak of damage to private property from erosion, we are not speaking of stream crossings, but what happens when riders make trails on lands that do not belong to them". This is back to illegal riding and has been discused in several other threads already.

MIke

[Sal]

When it collects in pools somewhere besides where it fell, it doesn't absorb into the gound, and in turn migrate to the "aquifer"?

no Dan, Pooled water evaporates instead of soaking into the ground.

Mike, groundwater recharges the aquifer. It also benefits the desert flora and fauna who rely on the rare desert rains to survive.

[MMM]

sal water collected in pools can have some water loss due to evaporation, but the majority of water is absorbed back into the ground. Follow just about any desert stream and it will vanish into the ground. Most water will be absorbed back into the ground, unless the ground has a high clay content or is mostly compacted rock or hard pan, in which case there will be few ruts left. Clay soils is the one exception, where ruts can form and trap the water and then will not be re-absorbed into the ground. Also, after major desert washout, a lot of water is left in pockets and unles the ground is hard or mostly rock, again it is absorbed into the ground. If this were not so the standard for building a spetic tank system test would not work. The "perk" test is where you dig a hole, fill it with water, allow the water to drain off into the ground, refill the hole and time how long it takes for the water to be absorbed.

Mike

[Dan]

When it collects in pools somewhere besides where it fell, it doesn't absorb into the gound, and in turn migrate to the "aquifer"?

no Dan, Pooled water evaporates instead of soaking into the ground.

Mike, groundwater recharges the aquifer. It also benefits the desert flora and fauna who rely on the rare desert rains to survive.

While I'm sure there is some evaporation, it pales in comparison with the amount of water which soaks down through sandy soil, especially on a rainy day. All low spots eventually become pooled water when it rains hard enough. But you cannot simply make the blanket statement that pooled water doesn't soak in. I've seen it myself.

[Sal]

Where do you see the pools? on man-made trails and roads. Absent the presence of trails, water runs in washes and soaks in and it collects in desert playas and soaks in. The spongey dirt (cryptobiotic soils) that is the top layer of desert soil absorbs water and releases it slowly to the plant and animal life over the next many months.

How do I know all this? I am a desert walker and see the magnificence of nature every day. If you only know the desert from the roadside or through a pair of goggles at speed, you may as well just ride in a wind tunnel...you are not seeing the magic that allows the wildlife to survive in a harsh environment.

[MMM]

Actually sal I have seen standing water (vernal pools) a lot in the desert. After just about every rain event a lot of water is left outdide the main wash and forms pools. Not an OHV track in sight. Even in ruts the water is channeled somewhere. To a pool, a main stream bed and there the water perks back into the ground. Sorry sal, this one is not going to cut it.

Mike

[Sal]

Mike, vernal pools is a term usually associated with uplands or beaches. In the desert they are called playas. The water is ephemeral (soaks in quick).

Nothing you have stated contradicts my assertion that OHV tracks contribute to erosion in the desert by diverting water away from the aquifer.

[MMM]

sal this is a quote about vernal pools.

"Temporary pools are found worldwide. Seasonally flooded habitats and their faunas share many common features, whether they occur in deserts, prairies, large river floodplains, alpine meadows, or temperate forests"

Link http://www.mwpubco.com/titles/vernalpools.htm

A photo of a desert vernal pool.

http://www.flickr.com/photos/lord_orman/3204255232/

Mike

[Sal]

call it what you want--we call'em playas in the Mojave. There is some evaporation here because the water is spread so shallow. However, the playas I have seen and visit on a regular basis support nearby growth of large Joshua trees.

The point I am making is that vehicle ruts allows water to run off into pools where it evaporates instead of being absorbed into the ground.

Shallow playas also allow water to pool up.

Should we allow OHV's to further contribute to the dessication of the desert by causing additional runoff?

[MMM]

sal, come on, admit it, some water may be lost due to evaporation but unless the pool of water is in rock, or some other really hard surface, some water will be absorbed.

http://www.britannica.com/EBchecked/top ... cteristics

Playa: "Physical characteristics"

Enclosed basins of salt and clay accumulation may originate from numerous causes. Tectonic causes include faulting, as in the East African Rift Valley and Death Valley, and warping, as in Lake Eyre in Australia, Lake Chad in central Africa, and Shaṭṭ al-Jarīd (Chott Djerid) in Tunisia. Wind deflation can produce shallow basins with downwind dunes, as in southeastern Australia. Even very large basins, such as the Qattara Depression of Egypt, have been ascribed to deflation. Local cataclysmic disruptions of drainage (e.g., volcanism, landslides, and meteorite impacts) may produce playas in desert regions.

Modern playa surfaces are not passive receptors of sediment as they were once believed to be. They serve as important sources of dust and salts, which are blown to the surrounding uplands. Complex assemblages of minerals and sediments occur on the playa surfaces. These directly reflect their environment of deposition and may be used to interpret ancient environmental conditions.

Two broad classes of playas may be defined on the basis of past histories. One type develops from the desiccation of a former lake. Sediments in such a playa are primarily lacustrine, rather than derived from modern depositional processes. The second type of playa has no paleolacustrine heritage. Small salt pans in South Africa, called vokils, are of this type.

The supply of material, basin depth, and duration of accumulation all contribute to variations in the thickness of playa deposits. Very thick playa sequences may have alternating layers of lacustrine clays and salt beds. The former generally reflect periods of high floodwater runoff into the closed basins, perhaps induced by higher rainfall (so-called pluvial periods). Saline sediments or pure evaporite beds reflect arid climatic phases. The precise climatic interpretation of paleolacustrine playa sequences, however, can be problematic.

Mike