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The Failure of Beaver Dams and Resulting Outburst Flooding: A Geomorphic Hazard of the Southeastern Piedmont
David R. Butler
Department of Geography University of Georgia Athens, Georgia 30602
ABSTRACT
Beaver are geomorphic agents through their building of dams and creation of pond environments. In the southeast United States, the successful reintroduction of beaver has vastly increased the number of ponds impounded by beaver dams. These dams may fail, producing rapid and potentially catastrophic draining of beaver ponds, a geomorphic hazard which has not gained sufficient notice.
This paper examines several cases of known dam failure and subsequent rapid drainage of beaver ponds. Reconstructions of the discharge from these ponds was accomplished using standard hydrologic relationships of stream dimensions or pond volume to discharge. Peak flood discharges may be catastrophically high . The maximum hazard for beaver-dam failure and pond outburstflooding occurs on the Piedmont, where periodic intense rainstorms combine with rapid surface runoff and limited surface infiltration to produce high-discharge floods.
KEY WORDS: beaver dam, flooding, geomorphic hazards, Piedmont, southeastern United States.
INTRODUCTION
The historical presence of native beaver (Castor canadensis) throughout the southeastern United States was of sufficient number to strongly impress early settlers in the region . Names such as Beaver Creek, Little Beaver Dam Creek, and Great Beaver Dam Creek appear on maps of Georgia that date back to 1780 (Parrish 1960). However, native beaver in the region were nearly exterminated during the late nineteenth and early twentieth centuries (Moore and Martin 1949, Parrish 1960, Johnson and Aldred 1984). In some areas in the southeast, beaver had in fact disappeared (Alabama Department of Conservation and Alabama Forest Products Association 1967, Taylor 1985). In the late 1930s through the early 1950s, southeastern state wildlife and conservation agencies successfully reintroduced the beaver. The conversion of many areas in the south-
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east from croplands to forestlands since World War Two has also played a sig nificant role in expanding potential beaver habitat (Anonymous 1986). Today, the beaver repopulation efforts in the southeast have proved so successful that many private and corporate landowners now consider the rodent to be a destructive pest, responsible for massive dollar amounts of timber destruction and flooding of cropland (Shipes et al. 1979, Forbus and Allen 1981 , Johnson and Aldred 1984, Anonymous 1986).
The reintroduction of the beaver in the southeast was done in part at least because of its geomorphic capabilities to reduce stream erosion and sediment transfer through the damming of streams and creation of pond environments, and to locally elevate the water table and reduce the effects of seasonally-fluctuating water table levels (Ruedemann and Schoonmaker 1938, Wilde et al. 1950, Apple et al. 1985, Johnston and Naiman 1987, Remillard et al. 1987). In areas of appropriate lithology (i.e., limestones and dolomites ), beaver ponds may act as agents of karstification by providing localized concentrations of water for solut ional work and capture by underground streams (Cowell 1984).
Although the literature cited above has provided some examination of the geomorph ic effects of the beaver and beaver dam construction, little attention has been given to the potential for natural hazards created by beaver-dam failure and subsequent catastrophic flooding . This paper examines that potential for rapid beaver-dam failure and pond drainage in the southeastern U.S" and presents historical examples and hydrologic reconstructions which illustrate the nature of the hazard .
Beaver Dams and Other Natural Dams
The formation and failure of natural dams have been recently reviewed by Costa and Schuster (1987). Obstructive natural dams include landslide dams, moraine dams, volcanic dams, glacier dams, fluviatile dams, coastal dams, eolian dams, and organic dams; this last category includes log and vegetation
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dams, and beaver dams (Costa and Schuster 1987 p. 2-3).
Floods from the failure of natural dams are usually much larger than floods of rainfall or snowmelt origin, but little is known of the processes of natural-dam failure (Costa 1985). However, through an examination of many cases of dam failure, Costa (1985) derived a series of regression equations to predict peak discharge for human-built, glacial, and landslide-dam failures. If, for example, the volume of water (V) which escapes a landslide dam is known, peak discharge (Q max) can be modelled as :
Q max = 672 Va.56 ; r2 = 0.73
Beaver dams are organic dams constructed normally of logs and brush weighted down with mud and stones (Warren 1932, Ives 1942, Neff 1959). Dam size and shape vary considerably, but a typical shape is a concave-upstream arch dam (lves 1942). Excellent photographs and schematic drawings of typical beaver dams may be found in Dugmore (1914) and Warren (1927) .
Beaver dams will break when stream discharge exceeds a critical strength threshold (Parker et al. 1985). Warren (1927 p. 50) mentioned that "the washing away of dams by floods are common happenings on our western streams, if not elsewhere," and Dugmore (1914) presented a newspaper account of an actual beaver-dam outburst flood. This flood caused landslides resulting in blockage of the main line of the Canadian Pacific railroad in eastern British Columbia. Dugmore (1914 p . 148) reported that :
"the slide, which was 300 feet wide and 30 feet deep, was caused by the bursting of an old beaver dam high up in the mountains ... the dam burst under the pressure of heavy rain storms last week .. . . Huge trees were brought down with the slide and boulders nearly as big as a box car made the job of clearing the track a difficult one. Some of the trees that came down bore the marks of the little animals' teeth, and the supports of
the dam erected by the beavers were plainly marked as such by the bleaching of their upper ends and the lower points coated with mud and slime."
Unfortunately, little recent attention has been given to beaver-dam failures. Costa (1985) did not examine them in any detail in his work, so no regression equation is available for beaver-dam failures . Costa ' s (1985) equat.j ons for landslide-dam failure provide the best substitute analogy for modelling discharge from beaver-dam failure.
Beaver-Dam Sites and Distribution in the Southeastern States
Beaver are present in every coastal southeastern state, here defined as North Carolina southwestward to and including Louisiana . They are concentrated primarily in the Piedmont and upper Coastal Plain physiographic regions, al though they are found to a lesser extent in the Appalachian highlands and lower Coastal Plain (Parrish 1960, Shipes et al. 1969, Johnson and Aldred 1984, Taylor 1985). The low number of beaver in these latter regions is attributable to sites which are geomorphically less favorable. In the lower Coastal Plain, stream beds consisting largely of loose sand with little plasticity offer poor foundations for establishment of dams and burrows (Parrish 1960). Beaver ponds do occur in the Coastal Plain along second and third order streams with wide floodplains (Shipes et al. 1979). where some finer-grained alluvium exists.
Beaver are also limited in number in the Appalachian Mountains in the southeastern states . There , swiftness of streams frequently precludes successful dam construction and maintenance, and an absence of mud in some areas of limestone lithology further reduces the likelihood of successful beaver-dam production (Parrish 1960, Taylor 1985).
Although actual statistical data are lacking from several states, areal coverage of beaver ponds formed by dam construction is impressive. An aerial pond survey in Alabama revealed over 10,000 beaver ponds covering over 95,000 acres, and affecting over 13,000 stream miles
(Alabama Department of Conservation and Alabama Forest Products Association 1967). Mississ ippi contains about 24,000 acres of beaver ponds, with four northeastern counties alone accounting for over 10,000 acres. Pond acreage estimates are not ava ilable for other states, although beaver are reported f rom "most of the Coastal Plain and Piedmont" in North Carolina (Taylor, 1985), in 28 of 46 counties in South Carolina (Sh ipes et al. 1979). in " virtually every county" in Georgia (Anonymous 1986), and in every county in the Florida panhandle (Alabama Department of Conservation and Alabama Forest Products Associ at ion 1967). Impoundments in Louisiana are believed to cover approximately oneeleventh the amount of their Alabama counterparts (Johnson and Ald red 1984).
Beaver-Dam Failures and Outburst Floods-Case Studies
Beaver ponds may lose water by evapo ration, percolation through the pond floor (Cowell 1984). " leakage through dams resulting from activ ity of semiaquatic mammals" such as otters (Reid et al. 1988), and leakage through or failure of dams as a result of water erosion . The last case, as discussed below, is hazardous and typically related to intense, short-term thunderstorms over localized areas.
Five cases of beaver-dam failure and flooding are known from northeast Georgia and western South Carolina, and are described below (Figure 1). Two of these cases occurred in separate inci dences in 1969 (sites 1 and 2, Figure 1). Two other ponds burst near Comer, Georgia, in the watershed of the Broad River (Site 3, Figure 1). after a period of very heavy rain in 1986 (R. Rogers, personal communication 1988). The final case took place on 7 September, 1987, when a beaver-dam outburst flood killed four people in Oglethorpe County, Georgia (S ite 4, Figure 1).
The 7969 Cases
Pullen (1971) examined several beaver ponds in Georgia and South Carolina during 1969. In the course of his investigations, he periodically revis ited
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o 500 I , I I
Kliomelers
D Coastal Plain D Piedmont ", \ Undifferentiated
Appalachian Highlands
~Other
Figure 1. Physiographic provinces of the southeastern states, and the locations of beaver-dam outburst floods . 1. Dyer Pond. 2. Railroad Pond. 3. Comer ponds. 4. Millstone Creek site.
several ponds. Two ponds, Dyer Pond and Railroad Pond, almost completely drained as a result of dam breakage between revisits. Dyer Pond is in .the drainage basin of Greenbrier Creek, in the Oconee River basin southwest of Athens , Georgia . Ra i lroad Pond , in the drainage basin of the Savannah River, is east of Augusta, Georgia, ne?r Aiken, South Carolina (Figure 1).
Dyer Pond was orig inally 4 acres in size. On an unspecified date in spring, 1969, but prior to a revisitation on 14 July, the pond 's water level lowered 3 feet and the acreage covered shrank to 0.2 acres " due to an unrepaired break in the dam" (Pullen 1971 p. 17). Railroad Pond 's water level dropped 2 feet in " the fall of 1969," and its acreage shrank from 3 to 0.2 acres.
As Pullen (1971 p. 27) noted, beaver dams in stream channels are very susceptible to being washed out by floodwaters. In order to determine the me-
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teorologic conditions most likely to cause dam failures and drainages of Dyer and Railroad Ponds, I consulted local -area weather records for the appropriate periods . In both cases, precip itation events of unusual intensity occurred, but only once, during the season when dam failure was known to have taken place (U.S. Department of Commerce 1969a, 1969b, 1969c).
Dyer Pond, known to have failed in spring, 1969, probably failed on or immediately after 15 April. Athens, Georgia, received between 2 and 3 inches of rain on that date (U.S. Department of Commerce 1969a), with almost 3 1/ 2 inches falling over the period of the 15th and 16th (Athens Daily News 19 April 1969) . Local rivers and streams produced "flash flooding in several areas as numerous streams overflowed their banks" (U.S. Department of Commerce 1969a p. 39). The absence of alternative heavy precipitation events allows tenta-
tive acceptance of the 15 April storm as the causal agent for the breaking of the dam on Greenbrier Creek containing Dyer Pond.
The maximum discharge of the Dyer Pond flood was calculated using Costa's (1985) formula for landslide dam failure. Volume reduction of the pond was cal culated at approximately 14,000 cubic meters, using Pullen's (1971) data on areal shrinkage and depth reduction (after conversion to metric for compatibil ity) . With Costa's equation,
Q max = 672 Va.56
where V = approximately 14,000 m3;
therefore,
the Dyer Pond Q max = approximately 62 m 3 sec- '.
Railroad Pond, South Carolina, likely failed on or soon after 3 September, 1969. Consultation of weather records for Augusta, Georgia, and Aiken, South Carolina (1969b 1969c) revealed a heavy downpour on that date, with 2.57 inches recorded on that date in Aiken, and over 4 inches in Augusta. As with the case of Dyer Pond, no other storm of suc~ intensity occurred during the general tlmeframe specified by Pullen (1971) .
The maximum discharge from the draining of Railroad Pond was calcu lated in the same fashion as for Dyer Pond. Railroad Pond underwent a volume reduction as a result of dam failure of 6900 cubic meters, which provides (via Costa 's equation) a Q max of approximately 41 cubic meters per second.
The Comer, Georgia, Cases
After a period of very heavy rain in 1986, two beaver dams failed and caused rapid drainage of adjacent pond.s. These ponds are within the town limits of Comer, Georgia (Figure 1). The larger of the two ponds was estimated as approximately 75 m x 30 m in area, and about 1.5m deep (R. Rogers, personal communication 1988). giving a volume drainage of 3,375 cubic meters. Based on Costa's (1985) landslide-dam failure formula, a maximum discharge of almost 28 cubic meters per second resulted.
The Mil/stone Creek Tragedy
The abandoned Echols Mill site on Millstone Creek is located in Oglethorpe County, Georgia, in the Broad River watershed approximately 30 km east of Athens, Georgia (Figure 1). The nearest recording weather station is in the county seat of Lexington, Georgia, 14 km southwest of the mill site. Heavy rains fell in the area of the headwaters of Millstone Creek on 7 September 1987, the Sunday of the Labor Day weekend. Lexington recorded 3.18 inches on this date (National Oceanic and Atmospheric Administration 1987).
Numerous beaver ponds formed by dams exist in the small tributary streams in the headwaters of Millstone Creek, and evidence of beaver activity is present throughout the area and along the course of the stream (Figure 2). Millstone Creek itself is typically a very placid stream, usually "two feet across and no deeper than the hubcaps of a car" (Ford and Veal 1987).
In order to more accurately quantify the typical stream discharge at the ford crossing where the disaster occurred, channel width, depth and velocity were measured at three positions along selected transects (Figure 3). Velocity was measured by timing a floating object over a 3 m course. Three velocity measurements were recorded and averaged. The channel depth measurements were also averaged. With measurements of width (W). depth (D). and velocity (V), discharge (Q) can be calculated using Leopold and Maddock's (1953) formula :
Q = WDV;
this calculation provided a discharge, as measured during a "typical" period of flow on 1 March 1988, of 0.28 cubic me-ters per second. . .
The creek flows in a channel which IS
essentially "perched" on solid granite bedrock which precludes effective incision. At several points along its course above the mill site, water depths never exceed 10 cm. Along the flanks of the creek, soil depth is typically less than 15 cm to granite bedrock, with granite out-
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Figure 2. Students examine a beaver-downed tree amidst flood debris on north side of Millstone Creek, upstream from the disaster site. Stream depth varies from 6 to approximately 20 cm in this reach .
cropping at the surface in many locations. Under such conditions, the natural stream flows almost as if in a flume, with no infiltration into the stream bed or banks.
On the night of 7 September 1987, at approximately 10:00 P.M. local time, six people in a Datsun automobile who had been picnicking at the abandoned mill site began to cross the creek at the ford site. Suddenly, rising waters stopped the car midstream (Ford and Veal 1987). The couples climbed out of the car and onto a large rock, where they shouted for help. The creek "swelled into a raging river," according to an eyewitness who had responded to the cries for help. A strong surge of water subsequently came along, which hit the rock, "made a big wave and washed them off" (Ford and Veal 1987 p. 6). A "wall of water" washed their car from where it was parked on the granite outcrop (approximately in the position of the truck in Figure 3) . When rescue
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crews arrived they found a "raging river." None of the victims were in sight. Large granite blocks from an adjacent quarry, some up to 1 m in diameter, were "being moved like cotton balls" (Oglethorpe County Sheriff's Department, personal communication Lexington, Georgia, 9 March 1988). Deputies from the Sheriff's Department found the car downstream about 100 yards from where it had been parked (Veal 1987). Two of the six people survived the flood. One of these was found "clinging rigidly to a tree more than 12 feet above the ground, where he told rescuers the waters tossed him" (Ford and Veal 1987 p. 1). The bodies of the four victims were found between a quarter and a half mile downstream from where they had been washed off the rock. The flood was attributed by the Sheriff to bursted beaver ponds from upstream, with the dams broken by the heavy Labor Day weekend rains.
Beavers can repair failed dams rap-
Figure 3. Stream depth considered typical by local authorities, as measured on 1 March 1988. Three measurements here revealed an average depth of 6.6 cm. Truck parked on exposed granite would have been underwater at height of flood.
idly (Reid et al. 1988), so rather than engage in a potentially futile search for a drained beaver pond from which vol ume and discharge could be calculated, I instead calculated the Millstone Creek flood discharge by measuring the areal cross-section (W x 0) of the flooded channel. The lateral limits of the flood were determined by walking along the channel and identifying where flood debris had been deposited in and around the bases of trees and other obstructions (Figure 4). Included within the flood debris were many logs and sticks which
had been completely denuded of their bark by beaver, possibly debris remnants from the collapsed dam upstream. Several logs which were covered with beaver teethmarks were recovered in the flood debris.
After locating the lateral margins of the flooded zone, the total width of the flooded area, and the depth of inundation at several locations along the widthmeasurement transect were measured. The margins may represent a minimum level only, because debris at higher levels may have been lost or removed dur-
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Figure 4. Flood debris on normally-dry granite slopes adjacent to Millstone Creek, 100 m downstream from the disaster site. Student in background would have been completely underwater during flood maximum.
ing the flood. Average depth and channel width were then multiplied by upper and lower velocity estimates derived from sediment competence curves, using the 1 m-diameter granite blocks as measures of the creek's erosive capability. Determination of discharge (Q) via W x D x V, with 2 m/second as the low estimated velocity, provided a minimum discharge of 72 cubic meters per second; determination with 9 m/second as the higher (and probably more realistic) estimated velocity gave a discharge of almost 325 cubic meters per second! In either case, it is clear that beaver-pond outburst floods from dam failures can produce flood peaks of dangerous proportions.
CONCLUSIONS
Beaver dams are both beneficial and potentially hazardous geomorphic agents. The dams create wetlands and assist in retarding surface runoff and erosion.
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However, beaver-dam failures and resultant floods are real geomorphic hazards in the southeastern United States, and also probably in other environments where beaver have become reestablished in the last few decades. In the southeast, locally heavy precipitation events and relatively steep topography produce a hazard that is probably greatest in the Piedmont region. Fewer beaver exist in the areas of steepest gradient in the Appalachian Moutains, so although environmental conditions there would produce maximum flood danger, the relative absence of beaver do not produce a significant hazard. On the Coastal Plain, soils possess a greater infiltration capacity. Streams there are less likely to be subjected to the flashiness of rapid drainage into a beaver pond capable of bursting a dam (Woodruff and Hewlett 1971). In the Piedmont, the hazard is at its maximum, particularly in those areas such as along Millstone
Creek, Georgia. Here, granite-floored stream channels produce natural flumes without infiltrational capabilities. Surface runoff into beaver ponds is also very rapid in these areas where infiltration capacity is limited.
The following conditions maximize beaver-pond outburst flooding: 1) occurrence immediately after a locallyheavy thunderstorm which has delivered 3+ inches of rain in less ·than 24 hours; 2) in areas of granite or other impervious rock outcrops where surface runoff is rapid and infiltration is limited; and 3) along relatively steep stream courses in the Piedmont.
ACKNOWLEDGEMENTS
wish to thank the students in my Geography 816 seminar for firing my interest in the beaver as a geomorphic agent, and for accompanying me to the Millstone Creek site during initial recon naissance. Christi Lambert was especially instrumental in the early class discussions on this topic, and Joe Nicholas of this group assisted in the fieldwork. The Department of Geography, University of Georgia, provided logistical and financial support for the study.
REFERENCES
Alabama Department of Conservation and Alabama Forest Products Association 1967. Alabama Beaver Symposium, Proceedings of the First Alabama Beaver Symposium, Montgomery, Alabama, 24- 25 October 1967, 51 pp.
Anonymous 1986. The Eager Beaver-Forestry 's Continuing Nuisance. Georgia Forestry, 39(1) : 6-7.
Apple, Larry L. , Bruce H. Smith, James D. Dunder, and Bruce W. Baker 1985. The use of beavers for riparian / aquatic habitat restoration of cold desert, gully-cut stream systems in southwestern Wyoming. In : Investigations on Beavers (ed. by G. Pilleri), Brain Anatomy Institute, Berne, Switzer· land, p. 123-130.
Athens Daily News, 19 April 1969. Rainy weather plagues Athens, Most of State. Page 1, Athens Daily News, Athens, Georgia.
Costa, John E. 1985. Floods from dam failures. U.S. Geological Survey Open-File Report 85·560, 54 pp.
Costa, John E., and Robert L. Schuster 1987.
The formation and failure of natural dams. U.S. Geological Survey Open-File Report 87-392, 39 pp.
Cowell, Daryl W. 1984. The Canadian Beaver, Castor canadensis, as a Geomorphic Agent in Karst Terrain. Canadian Field-Naturalist, 98(2) : 227-230.
Dugmore, A. Radclyffe 1914. The Romance of the Beaver. J. B. Lippincott Co., Philadelphia , 225 pp.
Forbus, Ken, and Allen Fred 1981 . Southern Beaver Control. Georgia Forest Research Paper 23, Research Division, Georgia Forestry Commission.
Ford, Wayne, and Karen Veal 1987. Sheriff: Bursted Beaver Ponds may have Led to Flood Killing 4. Athens Banner-Herald, 8 September 1987, p . 1 and 6, Athens, Georgia.
Ives, Ronald L. 1942. The Beaver-Meadow Complex. Journal of Geomorphology, 5(3): 191-203.
Johnson, Mark K., and Don R. Aldred 1984. Controlling Beaver in the Gulf Coastal Plain. Proceedings of the Annual Conference of the Southeastern Association of Fish and Wildlife Agencies 38, 189-196.
Johnston, Carol A., and Robert J. Naiman 1987. Boundary Dynamics at the AquaticTerrestrial Interface: The Influence of Beaver and Geomorphology. Landscape Ecology, 1(1): 47-57.
Leopold, Luna B., and Thomas Maddock, Jr. 1953. The Hydraulic Geometry of Stream Channels and some Physiographic Implications. U.S. Geological Survey Professional Paper 252.
Moore, George C., and Ernest C. Martin 1949. Status of Beaver in Alabama. Alabama Department of Conservation , Montgomery, Alabama, 30 pp.
National Oceanic and Atmospheric Administration 1987. Climatological Data, Georgia, September, 1987,91(9).
Neff, Don J. 1959. A Seventy-Year History of a Colorado Beaver Colony. Journal of Mammalpgy, 40(3): 381-387.
Oglethorpe County Sheriff's Department, 1988. Personal Communication, March 9, 1988.
Parker, Michael, Fred J. Wood, Jr., Bruce H. Smith, and Robert G. Elder, 1985. Erosional downcutting in lower order riparian ecosystems : have historical changes been caused by removal of beaver? In: U.S.D.A. Forest Service Technical Report RM-120, p.35-38.
Parrish, William F., Jr., 1960. Status of the Beaver (Castor canadensis carolinensis) in Georgia, 1959. Unpublished Master's Thesis, School of Forestry, University of Georgia, Athens, Georgia, 62 pp.
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Pullen, Thomas M ., Jr., 1971 . Some Effects of Beaver (Castor canadensis) and Beaver Pond Management on the Ecology and Utilization of Fish Populations along WarmWater Streams in Georgia and South Carolina. Unpublished Doctoral Dissertation, School of Forest Resources, University of Georgia, Athens, Georgia, 84 pp.
Reid , Donald G., Stephen M. Herrero, and Thomas E. Code, 1988. River Otters as Agents of Water Loss from Beaver ponds. Journal of Mammalogy, 69(1) : 100.- 107.
Remillard, Marguerite Madden, Gerhard K. Gruendling, and Donald J. Bogucki , 1987. Disturbance by beaver (Castor canadensis Kuh/) and Increased Landscape Heterogeneity. In : Landscape Heterogeneity and Disturbance (ed. by M. G. Turner) , Springer Verlag, New York, p. 103-23.
Rogers, Ronnie, 1988. Graduate Teaching Assistant, Department of Geography, University of Georgia, Athens . Personal com munication, 9 March 1988.
Ruedemann, Rudolf, and W. J. Schoonmaker, 1938. Beaver-Dams as Geologic Agents. Science, 88(2292) : 523- 525.
Shipes, Derrell A., T. T. Fendley, and H. S. Hill, 1979. Woody Vegetation as Food Items for South Carolina Coastal Plain Beaver. Proceedings of the Annual Conference of the Southeastern Association of Fish and
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Wildlife Agencies, 33 : 202- 211 . Taylor, Mark, 1985. The Beavers are Back.
Wildlife in North Carolina 49(9) : 22-27. U.S. Department of Commerce, 1969a. Cli
matological Data, Georgia, April, 1969, 73(4) .
U.S. Department of Commerce, 1969b. Climatological Data, Georgia, September, 1969, 73(9) .
U.S. Department of Commerce, 1969c. Climatological Data, South Carolina, September, 1969, 72(9).
Veal, Karen, 8 September 1987. 4 Die as Water Sweeps Car Down Vesta Creek. Athens Daily News, p. 1, Athens, Georgia.
Warren , Edward R., 1927. The Beaver-Its Work and Its Ways. Baltimore, American Society of Mammalogists, 177 pp.
Warren, Edward R. , 1932. The Abandonment and Reoccupation of Pond Sites by Beavers. Journal of Mammalogy, 13: 343-346.
Wilde, S. A. , C. T. Youngberg , and J. H. Hovind, 1950. Changes in Composition of Ground Water, Soil Fertility, and Forest Growth Produced by the Construction and Removal of Beaver Dams. Journal of Wildlife Management, 14(2) : 123-128.
Woodruff, James F., and J. D. Hewlett, 1971 . The Hydrologic Response of Small Basins in Georgia . Southeastern Geographer, 11(1) : 1-8.