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Earth Karst in the WatershedPART 2: LOSING STREAMS AND SINKHOLE-RIDDEN TERRAIN MAKES SURFACE WATER AND GROUND WATER ONE AND THE SAME. HOWELL COUNTY HAS SOME OF THE DEEPEST KARST IN THE OZARKSBy Denise Henderson Vaughn, West Plains Daily Quill Correspondent Groundwater Recharges Rapidly; Big Springs,
Deep Circulation So said James Vandike, hydrogeologist with the state's Division of Geology and Land Survey, author of a newly published 210 page book called "Groundwater Resources of Missouri.'' The better part of Howell County is one of those places Vandike was talking about, where surface and groundwater are one and the same. That means many wells in the county are, at times, basically drawing up surface water. Even deep city wells - despite the fact the city's six active wells range from 1,000 to 1,696 feet deep, with all but one cased down 700 feet or more. Mo. Department of Natural Resources (DNR) officials say they've done enough testing to be convinced that the area's groundwater is occasionally being influenced by surface water. At those times when water in the city wells becomes turbid, it contains microcontaminants, such as bacteria and algae, DNR says. But it is considered safe to drink because it is chlorinated. Why is this happening? The Quill visited Vandike at his Rolla office to try to find answers. One of the first clues is found on any area map. It's a "dry county''; all the big springs and cold flowing rivers are just outside the borders, a distance of 15 to 25 miles from the county's center. Vandike pointed out that most of the surface streams in Howell County and in much of the western part of Oregon County are losing streams; the flow goes underground. Howell County stands out on the map - that is, the map of losing streams in the Ozarks. It's all because of karst, Vandike explained. Karst topography: it's created when highly soluble layers of underground dolomite rock are fractured and dissolved by trickling water over the years until some cracks become crevices, and some trickles become torrents - creating sinkholes, caves, losing streams and springs. While karst topography is common throughout the Ozarks, the effects run deeper underground in central Howell County and into Oregon County than in most other areas, Vandike said. In his new book, he describes a band of intense karst development that is several miles wide and runs from a few miles south of Willow Springs, through West Plains, to Thayer. "Throughout this area the bedrock has been deeply weathered,
leading to the development of thick residuum, many losing streams and
numerous large sinkholes,'' Vandike writes. (Residuum is what's left after
bedrock breaks down by weathering - piled up clay and chunks of rock.)
Grand Gulf is near the southern end of this karst band, he said. "The
depth to which large openings go seems greater than in other areas,''
he told The Quill.
Vandike illustrates his conclusion with data taken from West Plains Well Number Two, which is no longer in service. Between 1958 and 1985, DNR operated a water level observation station at the well, located at Second and Washington Avenue. It was drilled in 1914 and is 1,305 feet deep. In order to watch the water level, a floating device is attached to a cable, which is in turn attached to a pen that continuously records water levels on a paper chart. Vandike wrote about it in his book. "Despite 800 feet of casing, groundwater levels will rise as much as 200 feet within a few hours after a major rainfall event in the area, and the well will produce water containing microorganisms that are characteristic of surface water and rapidly recharged groundwater'' he wrote. BIG SPRINGS, DEEP CIRCULATION Hydrologist Tom Aley, Protem, who did many of the dye tracings to area springs, adds this point. "In your area, you have three of the largest springs in the Ozarks. We know from dye tracings that the West Plains area is in the Mammoth Spring recharge area. Further north, around Willow Springs, is the recharge area for Greer Spring. Big Spring gets some of its water from the upstream parts of the Eleven Point River.'' Aley continued, "So, the whole area around West Plains is drained by extremely large springs. The explanation is deep groundwater flow. If there's just shallow groundwater circulation, springs can't get too large. To have large springs, you need a large recharge area. Deep groundwater circulation is linked to muddy wells at great depth.'' "To have a large spring, you need a large recharge area," Aley said. In many cases, this means robbing other areas of their surface streams. Hydrogeologist James Vandike, Rolla, just wrote a book on Missouri's groundwaters which explains the formula for estimating a spring's recharge area. It takes about 505 square miles to gather up enough water to supply Big Spring, he says. By comparison, Howell County covers 927 square miles. On the smaller end of the spectrum, a spring discharging about 10 gallons per minute would need a recharge area of only about 16 acres, and that land would most likely be close to the spring, Vandike explains. Vandike points out that although Big Spring is in the Current
River basin, most of its recharge originates outside it, primarily from
the Eleven Point basin. Flow measurements taken at gaging stations on
the two rivers confirm that the Eleven Point is carrying less, and Current
is carrying more, than the amount which could be accounted for by rainfall
hitting those watersheds. The difference in flow coincides fairly closely
to the flow of Big Spring, Vandike says. Huge areas of the Eleven Point
River's watershed are drained by losing streams.
HOWELL COUNTY PROVIDES RECHARGE FOR MAMMOTH AND GREER SPRINGS A fair part of northern Howell County appears to be in the recharge area for Missouri's second largest spring, Greer, which boils in two spots out of a gorge in Oregon County at a rate of 220 million gallons per day (344 cubic feet per second). It tumbles down a spring branch into the Eleven Point River, more than doubling that river's size. Dye from a 27-mile trace starting near Trask, and from a 34-mile trace from the headwaters of the Eleven Point River near Willow Springs both turned up at Greer Spring. Using Vandike's formula, The Quill estimates the spring's recharge area at 389 square miles. Mammoth Spring is at the head of the Spring River, just
into Arkansas south of Thayer. It produces about 155 million gallons per
day (240 cubic feet per second), and its recharge area seems to be about
272 square miles, or just under a third the size of Howell County, The
Quill estimates. Indeed, the county may provide the spring's main water
supply, since numerous dye tracings from central Howell County have all
led to Mammoth. The longest was a 32-mile trace, starting near Pomona
on Dry Creek, a tributary of the North Fork River. Other traces originated
near the West Plains city limits off BB Highway and at the former West
Plains sewage lagoon after it collapsed in 1978.
HIGH SCHOOL STUDENT DOES FIRST AREA TRACE CONNECTING GRAND GULF TO MAMMOTH SPRING Even before Aley's Big Spring traces, Toney Aid of West Plains had made in 1967 a successful seven-mile trace from Grand Gulf, near Thayer, to Mammoth Spring. His is the oldest trace listed in Vandike's new book. Grand Gulf, one of the area's most spectacular karst features, is a mile-long winding sinkhole with sheer bluffs on all sides, created by a cave collapse. A river runs through it most of the time, and after heavy rains it has been known to fill up and hold water for weeks at a time. "I'd heard stories, about how in the 1890s, you could walk back into the cave and see the river leading out of Grand Gulf," Aid told The Quill. "They said you could throw hay bales in and they'd come out at Mammoth Spring. But it was just folk tales; there was nobody still alive who'd done it. I wanted to see if I could prove it." Aid, then a student at West Plains High School, did the trace for a school science project. He got instructions and materials from state geologist Jerry Vineyard. "I waited for a big rain. It came at 2 a.m. one morning. I got there about 3 or 4 a.m. and climbed down the bluff by the overlook in the dark, then dropped in five pounds of flouroscein dye." Aid placed filter packets where water goes over the dam at Mammoth Spring, changing them twice a day, then sending them to Rolla to be tested. The dye hit the packets in a little over two days, Aid said. The school project netted Aid a NASA Science Foundation award and a trip to a national conference. Geologist Luella Owen explored Grand Gulf in the mid-1880s,
according to Vineyard's 1972 book, "Springs of Missouri." She describes
traveling by boat into the cave housing the large underground stream that
connects Grand Gulf to Mammoth Spring. Small white eyeless fish were "swimming
about the boat in astonishing multitude," Owen wrote. These were doubtless
the now-endangered Ozark blind cavefish. Access to the underground river
closed up in the early 1920s, when a severe storm washed big trees and
other debris across the cave opening, Vineyard wrote. WHERE DOES WEST PLAINS WELL WATER COME FROM? Bedrock in this whole area tilts to the southeast. And the groundwater in the Ozark aquifer, our water supply, flows on top of that tilted, nearly impervious bedrock. A major surface divide separates the White River basin from the Missouri River basin, and the groundwater is divided roughly along the same line, the map shows. The potentiometric map shows that the junction of Highway 14 and U.S. 63 sits along the southeastern edge of an oblong "flat area'' in the water table. The flat spot marks a divide; on the other side, groundwater drains to the southwest. The divide corresponds to the surface divide which separates the North Fork River from the Eleven Point and Spring River watersheds. Groundwater level falls quickly after it crosses over the edge of that flat spot along the divide, the map shows. The water table drops over 200 feet in about 5.5 miles, when measured between the 14/63 junction and the city's observation well at Second and Washington. By comparison, a quick look at a topo map shows the South Prong of the Jacks Fork River drops about 40 feet in that same distance. SINKHOLES UPSTREAM FROM CITY Numerous well-developed sink basins are in the area upgradient (upstream, in groundwater terms) from West Plains, including some in the land on top of the aforementioned groundwater divide, according to a local soil scientist who recently walked the area while mapping area soils. U.S. 63 cuts through the middle of a shallow 800-acre sinkhole just north of the Highway 14 junction. Part of this sink can be seen on the west side of the new lane, as it forms a muddy pond that holds water for quite some time after a rain. "That sink is well drained in other areas back away from the highway, but it got plugged up right there with sediment from the highway construction,'' explained the soil mapper. The soil scientist would not speculate on whether runoff into these sinkholes is contributing to groundwater supplying West Plains, saying, "It would probably take dye tracings from the surface to answer that question.'' The Quill has seen a June 1997 report, produced for the city of West Plains by the USDA Natural Resources Conservation Service office in Cabool. That agency does soil mapping. The writer noted he had observed a 3.5-inch rainfall while mapping in Galloway Creek watershed. That creek runs parallel to Holiday Lane and the railroad tracks, emptying into a sinkhole near Girdley Street and the tracks. "I observed that this watershed is quite karst in nature,''
he wrote. "This watershed also has many large areas where the natural
soil profile has been destroyed by earth-moving equipment. This is especially
the case in the Highway 63 corridor. Much of the soil surface in these
areas is a compacted clay with little or no vegetation. These areas are
contributing large amounts of water and sediment into Galloway Creek.
Covering these with a layer of topsoil and establishing vegetative cover
on them would slow down erosion and runoff,'' he wrote. He continued,
"I noted several drainageways that had large watersheds (160 acres plus)
that had no channels or debris after the 3.5-inch rain. I assume the runoff
had disappeared into a karst system.''
What do Grand Gulf, the old West Plains city dump and the Southern Hills Subdivision in Mountain View all have in common? Answer: they're all sinkholes. Curious holes in the ground throughout the region have long fascinated area residents. Sinkholes come in all shapes and sizes; they can be funnel-shaped, bowl-shaped, deep, shallow, or gentle depressions with slopes so gradual that they might go unnoticed, and sometimes they're ragged chasms with steep bluffs. Any depression in the ground formed because soil has been dissolved and removed through channels under the earth is considered a sinkhole; they all drain directly underground rather than to a surface stream. The Quill recently took a tour of sinkholes near West Plains. The guide was Mo. Department of Conservation (MDC) Forester Bob Cunningham, a keen observer who has had ample opportunity to tromp around much of Howell County, since part of his job is to assess forest health for private landowners. Soil is what makes trees grow, so wherever he goes, Cunningham pays attention to soils, geology and landforms. A stop on the tour was MDC's 240-acre Tingler Lake Conservation Area, south of town off U.S. 17, on County Road 8110. This lake is a water-filled sinkhole, Cunningham said, created when sediment filled in and sealed the five-acre lake's bottom hundreds or perhaps thousands of years ago. This is quite rare, as most nearby sinkholes drain rapidly to underground water channels. Not visited by The Quill, but also on public land is "The Sinks'' on U.S. Forest Service land off Highway CC, about 12 miles west of town. These are two dramatic steep-sided sinkholes, side by side, Cunningham said. One has a peat bog in the bottom. It may be reached by a hike through the woods off County Road 5150. Cunningham cautioned that climbing to the bottom of these is dangerous. "A fall down into there would really hurt. It's not for the faint of heart to go down there,'' he said. A "must see'' for anyone serious about visiting sinkholes is Grand Gulf State Park on Highway W, seven miles west of Thayer. It has been called "the Cadillac of sinkholes'' and "the little Grand Canyon.'' SINKHOLES GROW GREAT TREES As the "tour bus'' (a white MDC pickup) headed south on Highway 17, then turned left on the County Road 8800, Cunningham started pointing out swags and gently rolling areas. "Just driving around, you wouldn't necessarily notice that so much of central and southern Howell County doesn't drain into any creeks,'' he said. "You see rolling ground, but no V's for drainage.'' The well-known sinkholes are the dramatic deep ones with steep sides, but there's a lot more that go unnoticed because they're large, with gentle slopes, he said. Typically, they have few rocks, rich alluvial dirt, and they can grow great trees. "There's immense sink basins around here that you wouldn't notice, especially in areas where there's flat ground,'' he said. "They can cover hundreds of acres. They run from Pomona to West Plains and on toward Thayer.'' Sinkholes have many characteristics typical of creek bottoms, such as rich soil and moisture-loving plants, Cunningham observed. Some plant species that are uncommon in the rest of the county grow in some sinkhole areas, he said, including rose mallow, sedges and orchids, and trees like pin oak, shellbark hickory and bur oak. Cunningham stressed that trees and native plants should be left to grow in and around sinkholes, since vegetation slows erosion and helps filter rainwater. When that protective plant layer is peeled back and dirt exposed, he said, there is much greater chance of mud and pollutants entering the groundwater and potentially contaminating wells and springs which draw from that groundwater. "The bottom line is, if we don't take care of our surface
water, we'll all be drinking bottled water one of these days,'' he said.
The four-part Groundwater Series ran between
August 27 and September 2, 1998. The entire series, complete with maps
and photos, was reprinted in a special section. Reprints are free; mail orders need to include $1 for
postage and handling. |
