Quote:
Originally Posted by graciegirl
I don't think we can DO anything to prevent them and I don't see that anyone is to blame.
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Do any human activities induce sinkholes?
Sure. Sometimes in karst areas [irregular landscapes formed when soluble rocks like limestone dissolve], when you drill a well—looking for water or for mining purposes—as you're pulling water out of the ground, you're lowering the groundwater table. That creates almost a toilet-flushing effect. You're lowering that groundwater level, and the soil that was sitting above just falls out. That's one way.
We also induce sinkholes when we start putting up parking lots and buildings and changing what we call the hydrologic regime. Instead of the water naturally soaking into the ground, it's now running off and being concentrated—being put into the ground at one point. (See "Guatemala Sinkholes Created by Humans, Not Nature.")
From.
Why Sinkholes Open Up
4-Health Springs -- impacts of land use in a karst region
Health Springs serves as one of many examples where land-use activities in a karst terrane affect ground-water quality. The region contains coastal springs and karst uplands that are characterized by internal drainage and variable confinement between the surficial aquifer system and the Upper Floridan aquifer (fig. 9). Land use upgradient of the spring was used historically for citrus agriculture but at present includes an extensive golf course, a wastewater treatment facility, and residential and commercial properties. Activities at the wastewater treatment plant have included land application of dried sludge, spray irrigation and ponding of treated effluent. The site is presently planned for a county park; however, elevated nutrient and bacteria concentrations in the spring discharge have delayed this action.
Figure 9. - Sinkholes provide a direct hydrologic link between karst uplands and Health Springs along the coast.
Figure 9. - Sinkholes provide a direct hydrologic link between karst uplands and Health Springs along the coast (from Tihansky, 1999).
In April 1988, several cover-collapse sinkholes developed in an area where effluent from a wastewater treatment plant is sprayed for irrigation. Ponding of the effluent occurred while water levels were at their seasonal low. The maximum seasonal head difference combined with surface loading likely contributed to the formation of several sinkholes which drained the effluent into the ground-water system. Within several days of sinkhole formation, discharge at Health Springs, 2,500 ft downgradient, increased from 2 ft3/sec to 16 ft3/sec (Trommer 1992). A dye-tracer study confirmed the existence of a preferential ground-water flow path linking the upland spray field with the spring (Tihansky and Trommer, 1994). Dye injected into a well located in the sprayfield was detected in the spring water and in a well adjacent to the spring (fig. 10). Ground-water velocity was about 160 ft per day (ft/d) which is 250 times greater than estimates of the regional ground-water velocity (0.65 ft/d) in this area.
Background nitrate concentrations for ground water in Florida generally are less than 0.02 milligrams per liter (mg/L). Water samples collected at Health Springs since 1982 have nitrate concentrations ranging from 2 to more than 10 mg/L. These elevated values reflect the impact of land use in the spring's recharge area.
From
Karst Features and Hydrogeology in West-central Florida-A Field Perspective