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doi:10.3850/38WC092019-0765

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SEEPAGE ANALYSIS OF EARTHEN DAMS IN SOUTH CAROLINA WITH ANIMAL BURROWS

MELIH CALAMAK(1), LINDSEY A. LAROCQUE(2) & M. HANIF CHAUDHRY(3)

(1,2,3) University of South Carolina, Columbia, SC, USA

calamak@cec.sc.edu; larocqul@cec.sc.edu; chaudhry@sc.edu

ABSTRACT

The structural integrity of earthen dams in the natural habitat of wildlife is commonly affected by invasive animal burrowed into the embankment. The effects may be observed on the phreatic line, pore water pressures and seepage rate through the dam. This study investigates the effects of previously reported wildlife activities on two failed dams in the Midlands of South Carolina. Dam sites were visited to collect soil samples for geotechnical testing, measure the geometry, and make observations for animal presence. The dams are determined to have burrows by gophers and ant colonies from the inspection reports and site observations. To characterize the soils, geotechnical tests are conducted for grain size distribution, permeability, porosity, and liquid limit. The finite-element method is used to simulate the two-dimensional steady-state seepage at dams with isotropic and homogeneous soil assumption. A saturated/unsaturated soil model is used and Modified Kovacs and Mualem methods are utilized for the estimation of the volumetric water content function and hydraulic conductivity function, respectively. Pore water pressures, hydraulic gradients and seepage velocity are compared for intact and deteriorated structures to investigate the effects of animal activity. The results show that the animal burrows negatively impact the seepage behavior of the dams by affecting the pore water pressures, seepage rate, hydraulic gradients, and seepage velocities.

Keywords: Earthen dams, seepage modeling, burrowing animals, embankment safety, internal erosion.

1 INTRODUCTION In recent years, the interest in infrastructure and properties in the safety of dams has increased worldwide,

in order to reduce the loss of life and damage to the downstream regions. Flooding from failures of natural and constructed dam create a widespread hazard to people and property. Most of the dams on the National Inventory of Dams (NID) list are composed of natural erodible materials and may fail under extreme conditions, especially if the dams are not properly maintained and monitored (ASCE/EWRI Task Committee on Dam/Levee Breaching 2011). Hurricane Joaquin caused excessive rainfall and extensive flooding in the Midlands region of South Carolina in October of 2015, breached more than 40 earthen embankments. The most common cause of failures, as seen in the flooding in South Carolina, are overtopping, seepage, internal erosion and piping, and slope instability or a combination (Tabrizi et al., 2017). Although, the ASCE/EWRI Task Committee on dam and Levee Breaching reports that overtopping is the most common cause of embankment failure, piping or internal erosion is the most detrimental (Costa, 1985; Sharif et al., 2015). It is often cited as the most destructive among dam safety professionals because it is progressive and can rapidly lead to failure of the dam. Approximately 28% of all dam failures are due to piping (Costa, 1985; Sharif et al., 2015). Piping produces a widening hole through the embankment because of internal erosion. Internal erosion occurs due to the transport and migration of soil particles within the embankment structure. Understanding the internal erosion mechanism is difficult due to the complexity of the process and the difficulties of detection (Bendahmane et al., 2008).

Federal, local, and state agencies also investigate if animal activity is present and if the embankment needs reparation. Animal burrows may affect the integrity of the embankment, creating internal erosion. Mitigation of animal activity and researching the tendencies of each animal allows a better understanding of the internal erosion or piping occurring in the structures. Visible animal burrows in earthen dams are often included in dam safety inspection reports. A comprehensive understanding of the animal burrows and impacts on embankment integrity are required in order to minimize flooding due to dam failures. Burrowing species cause damage, water loss, and potentially flood by excavating earthen dams, flood control structures, and irrigation canals. The Federal Emergency Management Agency reported 23 main species among those posing a threat to earthen dams in 48 states (FEMA, 2005). Several animal species excavate burrows, tunnels, and den entrances for shelter, while other predatory animals enlarge these structures via digging in search of prey and some herbivorous species forage on vegetation growing on embankment dams (Bayoumi and Meguid, 2011). All these incidences create hollow spaces in the embankment which are catastrophic to the safety and performance of earthen dams, both on the surface and internally. In addition, multiple species burrowed within the

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embankment may destabilize the integrity and may create a tunnel from up to downstream, creating a passageway through the embankment (FEMA, 2005). The most significant and sometimes least obvious impact of species intrusion is the hydraulic alteration, which can manifest in different ways depending on the type and location of the intrusion, including the distortion of the phreatic surface. Dramatic changes to the phreatic surface can shorten seepage paths, increase seepage rates, decrease the factor of safety against slope failure and cause internal erosion of embankment material.

Few studies on the effects of burrowing animals active on earthen dams have been reported. Bayoumi and Meguid (2011) classified and summarized the invasive animals harmful to the embankments and defined their impacts. Embankment failures caused by animal activity were presented with their economic impacts resulting in excess of one billion dollars a year. Saghaee et al. (2012) conducted experimental research on the impacts of animal burrows in an earthen levee with a centrifuge model. The study found that the experimental model and the idealized animal burrows provided acceptable results. Saghaee et al. (2016) added pressure transducers into their previous experimental model to quantify the pore water pressures. It resulted in an altered phreatic surface and higher exit gradients, internal erosion and possible slope failures occurring at the levee toe. Saghaee et al. (2017) compared the findings of the previous experimental model with a three-dimensional numerical model. The numerical model of the study included a finite-element software simulating the seepage, stress distribution and slope stability. The slope stability analysis showed that the factor of safety of the upstream slope decreased by 25% due to the presence of burrows. Higher pore water pressures and larger exit gradients observed at the levee toe when the burrows were at lower elevations of the upstream side. Calamak et al. (2017a) conducted numerical simulations on the effects of animal burrows with the finite-element method by defining the shapes of burrows realistically using technical manuals and fact sheets on rodents. Seepage analyses were conducted on a hypothetical dam focusing on the pore water pressures, seepage face length and the seepage rate. It resulted that the elevations of the seepage path increase when there were burrows on the upstream slope and regardless of the animal type, the seepage rate through the dam increased.

The aim of this research is to study the effects of animal activity on the seepage behavior of two dams located in the Midlands of South Carolina, Barr Lake, and Lake Elizabeth. South Carolina Department of Health and Environmental Control (DHEC) reported these dams to have animal burrows. In the scope of the study, each dam site is visited to collect soil samples for material characterization. Geotechnical tests are conducted for the grain size distribution, hydraulic conductivity, porosity, and liquid limit of soils. The shape and geometry of animal burrows are gathered from the literature on wildlife and rodent animals. Numerical simulations of the two-dimensional, steady-state seepage are conducted with a finite-element software with a saturated/unsaturated soil model. Seepage is analyzed for both dams with and without the animal activity and pore water pressures and hydraulic gradients along the embankment are compared.

2 FIELD OBSERVATIONS DHEC oversees compliance for over 2,300 regulated dams in South Carolina which are classified based

on size and potential hazards (SCDHEC, 2019). Lexington and Richland Counties, located in the Midlands region of South Carolina, has over 200 regulated dams. This region suffered significantly in October 2015 during Hurricane Joaquin, a 1000-year rainfall event, causing extensive flooding and more than 40 breached embankments (Tabrizi et al., 2017).

DHEC dam safety reports are provided to the public via their website (SCDHEC, 2019). For every regulated dam in South Carolina a dam safety report is required, indicating any potential hazards, such as excessive vegetation, upstream and downstream erosion, settlement, and the presence of animal activity. In this study, two dams in the Midlands of South Carolina are selected based on animal activity indicated in the dam safety reports, including; Barr Lake and Lake Elizabeth dams. The inspections and site visits were conducted in 2014, 2015 and 2017. Figure 1 shows a map of the locations of the two dams studied located within Richland and Lexington Counties. Both Barr Lake, and Lake Elizabeth dams failed during the historic flooding in October of 2015. Animal activity was evident at both locations.

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Figure 1. Location of the dam sites.

Barr Lake is located within the Twelve Mile Creek Watershed, in Lexington County, SC. The October 2015 storm resulted in the breach of three more dams regulated by DHEC. Currently, a natural river flow passes through the breached dams. Prior to the flooding event, the presence of animal activity was indicated by DHEC and was listed as a significant hazard dam. In the inspection report from 2014, there were burrowed holes on the downstream slope and recent observations found that there were gopher burrows. Lake Elizabeth is located in the Upper Crane Creek watershed in the northern region of Richland County. Prior to the flooding event, a roadway was on the crest of the dam and was listed as a high hazard dam. Currently, a natural river flow passes through the breach area. The inspection reports indicated that there were holes on the upstream face of the dam. Further inspection of the dam showed evidence of activity of gophers and ants.

A laser distance measurement device (Bosch, Stuggart GLM40 with an accuracy of +/- 1.5 mm) was used to determine the embankment characteristics, including dam height, upstream and downstream slope, and crest width. The geometric characteristics of the dams considered are summarized in Table 1. Figure 2 shows photographic evidence of animal activity on the investigated dams. Animals were observed to be active on the crest of Barr Lake but not on Lake Elizabeth, on the upstream slope at Lake Elizabeth, and on the downstream side on both dams. In-situ soil samples were taken from multiple locations of each site for geotechnical investigations in the laboratory.

Table 1. The geometric characteristics of dams. Name Dam

height (m)

Crest width (m)

U/S slope D/S slope U/S water level (m)

Barr Lake Dam 4.30 4.00 1V:1.43H 1V:1.43H 3.7 Lake Elizabeth Dam 3.20 11.00 1V:2.0H 1V:4.0H 3.0

(a) Barr Lake Dam (b) Lake Elizabeth Dam (SCDHEC, 2019)Figure 2. Animal activities observed on dams.

In the southeastern region of the United States, there are more than 10 different types of animals or insects that cause extensive damage to earthen embankments (FEMA, 2005). Of the two sites that were investigated, two different species were observed during the site visits and listed in the reports, with multiple species on Lake Elizabeth. Table 2 lists the inspection dates, the location of the wildlife activity, and the species of the active animals on five dams, and Table 3, the animal species and the typical damage, shape, and location of each burrow.

Table 2. Summary of the animal activity. Name Inspection

dates Animal activity

Animal species

Barr Lake Dam 06-07-201410-10-2015

Crest and D/S slope

Gopher

Lake Elizabeth Dam 11-16-201410-10-2015

U/S slope, D/S slope

Gopher and ant

U/S: Upstream, D/S: Downstream

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Table 3. Typical damage to earth dams by animal species (FEMA, 2005; Tschinkel, 2011; OVLC, 2018) Species Typical damage Typical burrow

shape Typical active side

Gopher Gopher burrows cause internal erosion and structural integrity loss of earthen dams. Attracts predators (badgers), which burrow a larger den. Fan or horseshoe mounds can plug burrow entrances.

Hole diameters are around 8 cm

Downstream slope

Ant (Aphaenogaster treatae)

Colonies of ants consist of complex series of tunnels that exacerbate existing cracks and can “soften” the embankment threatening the structural integrity.

The nests ranged in size from two to seven chambers, 8 to 22 cm depth, and 11 to 80 cm2 total chamber area (Equivalent to 1.16 cm wide and 22 cm deep openings)

Crest, downstream slope

3 MATERIAL CHARACTERIZATION The collected soil samples from the two dams were tested for soil gradation, water content, permeability,

porosity, and the liquid limit for the material characterization. All geotechnical experiments were conducted with reference to Bardet (1997). The soil gradation was determined using a standard sieve analysis for the sediment coarser than 0.075 mm and Coulter Counter tests (Beckman Coulter, 2009) for particles finer than 0.075 mm. The coefficient of curvature, 𝐶𝑐 = (𝐷30)2/(𝐷10 × 𝐷60), the coefficient of uniformity, 𝐶𝑢 = 𝐷60/𝐷10, and 𝐷𝑥 =grain

size such that 𝑥 % of the sediment is finer were determined. The soil types were determined using the Unified Soil Classification System and are presented in Table 4.

The water content of soils, w, was measured using the oven-drying method. The hydraulic conductivity, K, of soils was determined with the constant head test, whereas the porosity was measured with a graduated cylinder and water. The liquid limit tests were performed with Casagrande apparatus. The summary of the results for geotechnical tests can be seen in Table 4.

Table 4. The geotechnical characteristics of embankment soils. Name D10

(mm) D60 (mm)

Cu Cc K (m/s)

w (%)

Porosity Liquid limit (%)

Type

Barr Lake 0.02 0.5 25.00 4.00 2.01×10-5 17.8 0.45 15.25 SC-SM

Lake Elizabeth 0.0072 0.23 31.94 13.59 3.99×10-6 13.6 0.43 42.34 SC-SM

4 NUMERICAL MODELING The two-dimensional flow through an embankment can be defined by Darcy’s law with the following

equation given in Cartesian coordinates (Richards, 1931; Papagianakis and Fredlund, 1984). 𝜕

𝜕𝑥(𝐾𝑥

𝜕𝐻′

𝜕𝑥) +

𝜕

𝜕𝑦(𝐾𝑦

𝜕𝐻′

𝜕𝑦) + 𝑄′ =

𝜕𝜃

𝜕𝑡[1]

in which H' is the total head, Kx and Ky, are the hydraulic conductivities in x and y directions, respectively, Q' is the external boundary flux, θ is the volumetric water content, and t is the time. Eq. (1) can be solved with a proper numerical technique to simulate the seepage in embankments. The solution of this equation is commonly carried out using the finite-element method and gives the pore water pressures and the total heads. The hydraulic gradients, velocity and flow rates through the body can be obtained with additional computations. The current study utilized SEEP/W, a software applicable to steady/unsteady and saturated/unsaturated seepage problems under various hydraulic conditions (Geo-Slope Int Ltd, 2013), for modeling two-dimensional seepage in dams. It is based on the finite-element method and commonly used in geotechnical and hydraulic engineering problems (Calamak and Yanmaz, 2017; Calamak et al., 2017b; Liu et al., 2017). The hydraulic conductivity differs significantly, depending on the degree of the saturation of the soil and there is some seepage in the unsaturated zone. Therefore, a saturated/unsaturated soil model is used to realistically simulate the flow. The function of the volumetric water content and hydraulic conductivity can be estimated by empirical and semi-empirical equations in the literature. In this study, the water content function is estimated by the modified Kovacs method (Aubertin et al., 2003) using the grain size distribution data of soils. This technique uses D10, D60 and liquid limit of soils to estimate the degree of saturation. This is then used to determine the volumetric water content function (Kovacs, 1981; Aubertin et al., 2003; Geo-Slope Int Ltd., 2013). The hydraulic conductivity function is described using the volumetric water content function by Mualem method (Mualem, 1976).

In modeling, both dams are considered to be under normal operating conditions with the normal upstream water level and no tailwater on the downstream side. The focus is on the seepage through the embankment.

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Therefore, the foundation is assumed to be impervious for both dams. The simulations are conducted withhomogeneous and isotropic material assumption under steady-state boundary conditions. The animal burrowsare introduced as hollow spaces in the finite-element model using their realistic shapes. Quadrilaterals andtriangles are used to generate the finite-element solution mesh with a maximum element size of 0.1 m. Thefinite element model of Barr Lake Dam with mesh properties and boundary conditions are given in Figure 3. Thetotal number of nodes and elements was 4,505 and 4,351, respectively for Barr Lake Dam and 6,955 and 6,671,respectively for Lake Elizabeth Dam.

Figure 3. The finite element model of Barr Lake.

5 RESULTS AND DISCUSSION The seepage results for both the intact and deteriorated dams are presented in this section. The phreatic

surface of seepage for intact and deteriorated embankments of Barr Lake are shown in Figures 4 (a) and (b), respectively. In the figures, five points are selected, i.e. Points 1-5, at the same location for with and without animal burrows. These points are positioned along the phreatic line, located on the upstream and downstream sides and represent both saturated and unsaturated zones. At these points, the pore water pressure, hydraulic gradient and seepage velocity are computed and the variations of these parameters are analyzed. Observations of the figures showed that the phreatic surface is altered due to the presence of burrows for both dams. Each point across the embankment showed a decrease in the total head.

The percent change in pore water pressures, hydraulic gradients, and seepage velocity at every point for both dams are shown in Table 5. The locations of the selected points across the embankment is expressed in terms of the ratio of the position of the point to the corresponding dimension. The horizontal location of the point is given as the ratio of the distance from the heel to the dam base width, B, whereas the vertical location is expressed as the ratio of the height of the point from heel to the total dam height, H. Negative values indicate a decrease in value from no animal activity to the presence of animal activity and a positive indicates an increase in value. It is seen that the presence of animal activity affects seepage parameters. The results presented in Table 5 show that the presence of gopher burrows on the downstream reduce the pore water pressures up to 38% near the toe. A reduction in pore water pressures is also observed in the upstream area. However, this may be due to animal activity not being present in the upstream area. The hydraulic gradients across the embankment are observed to increase at most of the points for both dams. The seepage velocity for Barr Lake shows an overall decrease, whereas Lake Elizabeth shows an increase. This may be attributed to the multiple species on Lake Elizabeth.

(a) (b) Figure 4. The phreatic surface of Barr Lake (a) without animal activity; (b) with animal activity.

Table 5. The comparison of pore water pressures, hydraulic gradients and flow velocities at selected points. Change in

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Point x/B y/H Pore water pressure

(%)

Hydraulic gradient

(%)

Seepage velocity

(%)

Barr

Lake

Dam

1 0.41 0.71 -12.22 9.35 9.36 2 0.52 0.72 -41.34 10.34 -33.383 0.70 0.42 -35.86 15.68 15.684 0.87 0.14 -33.18 -27.98 -27.945 0.96 0.05 -6.27 -10.43 -10.44

Lake

Eliz

abeth

Dam

1 0.24 0.78 -8.64 1.71 1.70

2 0.42 0.84 -24.87 7.99 0.09

3 0.64 0.51 -34.76 10.17 10.17

4 0.86 0.16 -37.98 14.70 14.69

5 0.96 0.07 -8.47 -6.20 -6.20

B: Base width of the dam; H: Height of the dam

In addition to the comparisons with and without burrows at designated locations, the seepage rate at the dam centerline, CL, the flow velocity, and the hydraulic gradient were calculated and are listed in Table 6. For each earthen dam, there is an increase of seepage rate, velocity, and hydraulic gradient with the existence of animal activity. The percent increase is calculated for (1) seepage rate as 8% for Barr Lake and 14% for Lake Elizabeth, (2) maximum seepage velocity as 46% for Barr Lake and 244% for Lake Elizabeth, (3) maximum hydraulic gradient as 43% for Barr Lake and 264% for Lake Elizabeth.

Table 6. The effect of animal burrows on the seepage rate, velocity, and the maximum gradient.

w/o burrows w/ burrows

Seepage rate

at the CL (m3/day)

Maximum seepage velocity (m/day)

Maximum hydraulic gradient

Seepage rate

at the CL (l/day)

Maximum seepage velocity (m/day)

Maximum hydraulic gradient

Barr Lake 1.11 1.21 0.70 1.20 1.77 1.00

Lake Elizabeth Dam

0.07 0.09 0.25 0.08 0.31 0.91

CL: Centerline

6 CONCLUSION The impacts of rodent animals burrowing into embankments were investigated for the seepage through

earthen dams. To this end, two dams located in the Midlands of South Carolina, Lake Elizabeth and Barr Lake, which were previously subjected to animal activity were selected. Animal species which were active on the dams were identified from the inspection reports and site visits. The shape and size of animal burrows were obtained from the related literature. Soil samples were collected from the dam sites and six different geotechnical tests were conducted to determine the soil properties. Two-dimensional, steady-state seepage flow through deteriorated dams was simulated using the finite-element method with a saturated/unsaturated soil model. Analyses were held for both deteriorated and intact dams to show the impacts of animal burrows. The pore water pressures, hydraulic gradients and seepage velocities across the embankments were computed and compared for two cases.

It was found that the animal burrows in close vicinity of the dam toe reduce the pore water pressures around the toe up to 38%. This effect is also extended towards the upstream if there is no or a small burrow there. The hydraulic gradients and seepage velocities commonly increase across the embankment due to animal burrows. Specifically, the increase in the maximum gradient is substantial. The seepage rate at the dam centerline also increases slightly.

The results and findings of this study are limited by the location, the geometric and material characteristics of the investigated dams. Therefore, it should be kept in mind that they are site-specific, and their generalization needs extensive analyses of different earthen dams.

ACKNOWLEDGMENTS The authors would like to thank William Ovalle-Villamil and Pitak Ruttithivaphanich for their assistance in

geotechnical laboratory tests, and Lareb Khan and Sloan Jackson for their help in the laboratory.

REFERENCES ASCE/EWRI Task Committee on Dam/Levee Breaching. (2011). Earthen embankment breaching. Journal of

hydraulic engineering, 137(12), 1549-1564. Aubertin, M., Mbonimpa, M., Bussière, B., & Chapuis, R. P. (2003). A model to predict the water retention curve from basic geotechnical properties. Canadian Geotechnical Journal, 40(6), 1104-1122.

Aubertin, M., Mbonimpa, M., Bussière, B., & Chapuis, R. P. (2003). A model to predict the water retention curve from basic geotechnical properties. Canadian Geotechnical Journal, 40(6), 1104-1122.

E-proceedings of the 38th IAHR World CongressSeptember 1-6, 2019, Panama City, Panama

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Bardet, J. P. (1997). Experimental soil mechanics. Prentice Hall.Bayoumi, A., & Meguid, M.A. (2011). Wildlife and safety of earthen structures: a review. Journal of Failure

Analysis and Prevention, 11(4), 295-319. Beckman Coulter. (2009). The Higher Resolution for Particle Sizing and Counting: Multisizer Coulter Counter.

Fullerton, CA. USA, 12pp. Bendahmane, F., Marot, D., and Alexis, A. (2008). “Experimental parametric study of suffusion and backward

erosion.” J. Geotech. Geoenviron. Eng., 10.1061/(ASCE)1090-0241(2008)134:1(57), 57–67. Calamak, M., & A. M. Yanmaz. (2017). Uncertainty quantification of transient unsaturated seepage through

embankment dams. International Journal of Geomechanics, 17(6), 4016125. https://doi.org/10.1061/(ASCE)GM.1943-5622 .0000823.

Calamak, M., Bilgin, G., Demirkapu, H., and Kobal, A. (2017a). Effects of Burrowing Animals on Seepage Behavior of Earthen Dams. In 16th World Water Congress, IWRA (International Water Resources Association), Cancun, Mexico (pp. 1-11).

Calamak, M., Yanmaz, A.M., & Kentel, E. (2017b). Probabilistic evaluation of the effects of uncertainty in transient seepage parameters. Journal of Geotechnical and Geoenvironmental Engineering, 143 (9), 6017009. https://doi.org/10.1061 /(ASCE)GT.1943-5606.0001739.

Costa, J. E. (1985). “Floods from dam failures.” U.S. Geological Survey Open-File Rep. 85-560, Denver, 54. FEMA. (2005). Technical Manual for Dam Owners: Impacts of Animals on Earthen Dams, pp: 1–115.

Management Agency (FEMA) and the Association of State Dam Safety Officials. FEMA 534/September 2005

Geo-Slope Int Ltd. (2013). Seepage Modeling with SEEP/W. Geo-Slope International Ltd., Calgary. Kovács, G. (1981). Seepage hydraulics. Elsevier Science Publishers, Amsterdam. Liu, L.L., Cheng, Y.M., Jiang, S.H., Zhang, S.H., Wang, X.M., & Wu. Z.H. (2017). Effects of spatial

autocorrelation structure of permeability on seepage through an embankment on a soil foundation. Computers and Geotechnics, 87: 62–75. https://doi.org/10.1016/j.compgeo.2017.02.007.

Mualem, Y. (1976). A new model for predicting the hydraulic conductivity of unsaturated porous media. Water Resources Research, 12(3), 513-522.

Ojai Valley Land Conservancy (OVLC). (2018). Botta’s Pocket Gopher – OVLC: OVLC. Available from https://ovlc.org/ojai-wildlife/bottas-pocket-gopher/ [cited 9 May 2018].

Papagianakis, A. T., & Fredlund, D. G. (1984). A steady state model for flow in saturated–unsaturated soils. Canadian Geotechnical Journal, 21(3), 419-430.

Richards, L. A. (1931). Capillary conduction of liquids through porous mediums. Physics, 1(5), 318-333. Saghaee, G., Meguid, M.A., & Bayoumi, A. (2012). An experimental procedure to study the impact of animal

burrows on existing levee structures. In Proceeding of the 2nd European Conference on Physical Modelling in Geotechnics, Delft, the Netherlands (pp. 23-24).

Saghaee, G., Mousa, A.A., and Meguid, M.A. (2016). Experimental evaluation of the performance of earth levees deteriorated by wildlife activities. Acta Geotechnica, 11(1), 83-93.

Saghaee, G., Mousa, A.A., and Meguid, M.A. (2017). Plausible failure mechanisms of wildlife-damaged earth levees: insights from centrifuge modeling and numerical analysis. Canadian geotechnical journal, 54(10), 1496-1508.

South Carolina Department of Health and Environmental Control (SCDHEC). (2019). Final Dam Inspection Reports. Available online at https://scdhec.gov/disaster-preparedness/hurricanes-floods/sc-flood-information/final-dam-inspection-reports

Sharif, Y.A., Elkholy, M., Hanif Chaudhry, M., & Imran, J. (2015). Experimental study on the piping erosion process in earthen embankments. Journal of Hydraulic Engineering, 141(7), 04015012.

Tabrizi, A.A., LaRocque, L.A., Chaudhry, M.H., Viparelli, E., & Imran, J. (2017). Embankment Failures during the Historic October 2015 Flood in South Carolina: Case Study. Journal of Hydraulic Engineering, 143(8), 05017001.

Tschinkel, W.R. (2011). The nest architecture of three species of north Florida Aphaenogaster ants. Journal of Insect Science, 11(1), 105.