Вода из реки в Кентукки исчезала на два года, прежде чем вернуться из-за шахтных трещин

From 1985 to 1992, USGS injected dye near Kentucky’s Fishtrap Lake; trapped dye reappeared up to 2 years later as rain flushed mining-fractured rockComments AA Text Size Small Medium Large AI-generated representative image. Researchers add dye to the Fishtrap River to trace water movement and study its flow. Image credits: ChatGPT Near Fishtrap Lake in Pike County, Kentucky, the U.S. Geological Survey spent years investigating what happens to water after it disappears into fractured rock. Researchers used fluorescent dyes to track the groundwater path. Between 1985 and 1992, USGS researchers injected dye into a core hole that penetrated shallow and mining-induced fractures near the crest of the ridge. To determine where the dye travelled, how quickly it moved and why some of it seemed to disappear before returning months or even years later, they monitored the water from a network of piezometers. The findings of the 1994 USGS report showed that groundwater movement in the fractured, coal-bearing rocks was far more complicated than a simple downflow.Researchers monitored a dye trail through fractured coal-bearing rocksA preliminary 1985 injection studied by the USGS laid the groundwork for the subsequent Fishtrap Lake experiment. In the initial experiment in 1985, researchers injected fluorescent dye into a 61-foot-deep ridge-top well. The dye was then detected in varying concentrations in all of the downgradient piezometers within several days. According to the USGS, that earlier result illustrated that groundwater could move toward areas of lower head through a complex system of near-vertical fractures and permeable coal beds.Later investigation in 1985-92 examined the ground system in greater detail, as fluorescent dye was introduced through a core hole that penetrated near-surface fractures alongside fractures that were associated with earlier mining activities. Water samples were collected from piezometers positioned in conductive fracture zones and fractured coal beds at different depths. By monitoring dye concentrations and water levels over time, hydrologists could track how the tracer moved through the subsurface and identify changes in its pathway. An aerial view of Fishtrap Lake in Pike County, Kentucky, showing the region's massive federal government-managed reservoir infrastructure.Image Credit: the U.S. Army Corps of Engineers The depth monitoring network indicated that there was not just a single underground route. The researchers found that the dye movement was influenced by the distribution and interconnection of fractures, their hydraulic properties, the water pressure when the dye was injected, and subsequent changes in the groundwater recharge. Rather than forming one continuous plume, the dye could split among several fracture-controlled pathways, producing complex multi-peaked concentration curves as different pulses of dye-labelled water reached monitoring stations at different times.This suggested that when the groundwater levels were relatively high or rising, dye could travel faster from near-surface fractures to monitoring wells, with some arriving within days or weeks. On the other hand, injections made when the hydraulic heads were low behaved differently. Some of the dye remained trapped in what the organisation described as hydraulically dead zones: water-depleted fractures where movement was temporarily limited.Groundwater recharge plays a role hereThe disappearance of the dye did not necessarily mean that it had vanished from the groundwater system, though. Instead, some tracer remained in storage within poorly connected or water-depleted fractures, and as observed by the organisation, a subsequent increase in recharge could remobilise the residual dye and carry it back into active pathways. Some stored dyes were transported over periods ranging from several months to about two years after the initial injection.Thus, rainfall could influence not only how much groundwater was moving but also when previously stored material would re-enter the system. Increased recharge changed hydraulic gradients and could speed the movement of dye along established fracture pathways. Meanwhile, declining recharge could slow it. In effect, the underground rock system could temporarily store parts of the tracer and later release it when hydrologic conditions changed.The USGS further reported that an abandoned underground mine and subsidence-related surface cracks extended to within about 250 feet of the principal dye-injection core hole. The altered natural fractures because of mining created pathways and changed the existing hydraulic connections. In two tracer tests, investigators reached the conclusion that mining-induced fractures had propagated far enough to breach the annular seal around the core hole, requiring researchers to mathematically isolate this localised vertical bypass from the true horizontal fracture velocities. End of Article Follow Us On Social Media