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Home My WebLink AboutAPA1215Susitna . Hydroelectnc ----------·--, ___ ..;___ __ ---------- Prepared 'Jy: ae�,�� 1 l��u 1 ----- SUStT�iA �fYDAOELEC .. ft1�C PROJECT 1"ASK 2 -SURVEY AND SITE FAC'L ITiES SUB"rASK 2.15-SUJPE STABILITY P�r�D EROSION STUDIES CLOSEOU1' J"ii�PORT Fll\�A'-DRAFT Mi\RGH 198� ' I _I Prepared by: [i] SUSITNA HYDROELECTRIC PROJECT RESERVOIR SLOPE STABILITY TASK 2-SURVEY AND SITE FACILITIES SUBTASK 2.15-SLOPE STABILITY AND EROSION STUDIES CLOSEOUT REPORT FINAL DRAFT MARCH 1982 I I .____._ ___ -_-ALASKA POWER AUTHORITY __ ---J Prepared by: • SUSITNA HYDROELECTRIC PROJECT RESERVOIR SLOPE STABILITY TASK 2-SURVEY AND SITE FACILIT IES SUBTASK 2.15-SLOPE STABILITY AND -- EROSION STUDIES CLOS EOUT REPORT FINAL DR AFT MARCH 1982 HARZA-EBASCO Susitna Joint Venture Document Number 89s Please Return To DOCUMENT CONTROl ......___ __ ALASKA POWER AUTHORITY __ ____. TABLE OF CONTENTS 1 -INTRODUCTION • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 1-l 2 -SUMMARY ANU CONCLUSIONS ••••••••••••••••••••••••••••••••••••• 2-l 3 -METHODOLOGY • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 3-l 4 -SLOPE STABILITY • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 4 4.1 -Changes in Ground Water Regime • • • • • • • • • • • • • • • • • • • • • • • • 4-l 4.2-Permafrost Thaw ••••••••••••••••••••••••••••••••••••••• 4-2 5 -RESERVOIR GEOLOGY • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 5 5.1 -Watana • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 5-l ( a ) Surf i c i a l Ge o l o gy • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 5-l (b) Bedrock Geology ••• • •• •• •• •• • • ••• • • •• •• • •• • • • • •• • • 5-1 (c) Slope Stability and Erosion •••••••••••••••••••••• 5-2 5. 2 -Oev i l Canyon • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 5-4 (a) Surficial and Bedrock Geology • • • • • • •• • • • • • • • •• • • • 5-4 (b) Slope Stability and Erosion •••••••••••••••••••••• 5-5 6 -RECOMMENDATIONS • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 6-1 LIST OF FIGURES Figure 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.10 5.11 5.12 5.13 Title Typical Slope Failure Slope Conditions in a Dry Cohesionless Soil Submerged Slope Conditions in a Cohesionless Soil Slope Conditions, Seepage Parallel to Slope in Cohensionless Soil Slope Conditios in a Soil with Cohesion Slope Conditions in Rock Model for Thawing of Permafrost Conditions in a Thawing Slope Slope Models for Watana and Devil Canyon Reservoirs (Models I, I I) Slope Models for Watana and Devil Canyon Reservoirs (Mode 1 s II I, IV) Watana Reservoir Index Map Watana Slope Stability Map Watana Slope Stability Map Watana Slope Stability Map Watana Slope Stability Map Watana Slope Stability Map Watana Slope Stability Map Watana Slope Stability Map Watana Slope Stability Map Watana Slope Stability Map Watana Slope Stability Map LIST OF FIGURES (Cont•d) Figure 5.14 5.15 5.16 5.17 5.18 5.19 5.20 5.21 5.22 5.23 5.24 5.25 5.26 5.27 5.28 5.29 5.30 5.31 5.32 5.33 5.34 Title Watana Slope Stability Map Watana Slope Stability Map Watana Reservoir Index Map Watana Slope Stability Map Watana Slope Stability Map Section F-F Watana Reservoir Potential Rotational Slides and Flows Section G-G Watana Reservoir Area of Flow Failures Section E-E Watana Reservoir Area of Potential Flows Section 0-D Watana Reservoir Potential Beaching Devil Canyon Reservoir Index Map Devil Canyon Slope Stability Map Devil Canyon Slope Stability Map Devil Canyon Slope Stability Map Devil Canyon Slope Stability Map Devil Canyon Slope Stability Map Devil Canyon Slope Stability Map Oevi 1 Canyon Slope Stabi1 ity f•lap Devil Canyon Slope Stability Map Section B-B Devil Canyon Reservoir Potential Minor tieaching Section A-A Devil Canyon Reservoir Potential Minor Beaching Section C-C Devil Canyon Reservoir Potential large Slide LIST OF TABLES Table Title 5.1 Characteristics of Slope Materials 1 INTRODUCTION The immediate effect of the filling of the Watana and Devil Canyon Reservoirs on the impoundment slopes will be twofold, the modification of the ground water regime and hence the modification of the balance of driving and resisting forces in the slope and the initiation of thawing in permafrost slopes. The perform- ance of these slopes after impounding will be governed by the effect of flooding on the external factors which have contributed to instability in the past and the rate of permafrost thaw. Little or no research has been done on large northern reservoirs in tne sub- artie climatic zone that is subject to permafrost conditions (Newbury, 1978). Impounding of the Susitna River Valley and its tributaries will influence the slope stability of both the Devil Canyon and Watana Reservoirs. Currently on the slopes above the river, evidence of shallow landslides and the presence of discontinuous ·permafrost imply that instability will also occur during the im- pounding of these reservoirs. Slopes in thawing permafrost and in frozen soils will add to the complexity and sensitivity of the slopes in stability analysis and therefore in predicting the conditions of the slopes after impounding. Shoreline erosions will occur as a result of two geologic processes; (1) beach- ing and (2) mass movements. The types of mass movement encountered in a perma- frost terrain which are pertinent to this study are described below (Varnes, 1958, modified by McRoberts and Morgenstern, 1974). flows - a broad type of movement that exhibits the characteristics of a vis- cous fluid in its downslope motion. solifluction-movements restricted to an active layer and generally require fine grained soils. skin flows -detachment of a thin veneer of vegetation and mineral soil and subsequent movement over a planar inclined surface. bimodal flows -movement with a distinctive biangular profile com- posed of a steep headscarp and a low angle tongue. multiple regressive flow -forms a series of arcuate, concave down- slope ridges as it retains some portion of the prefailure relief. slides-landslides exhibiting a more coherent displacement, a greater appearance of rigid-body motion. block slides -movement of a large block that has moved out and down with varying degrees of backtilting; coherent displacement. multiple regressive slides -series of a arcuate blocks concave towards the toe, that step backward higher and higher toward the headscarp. rotational slides-landslides which occur in tnawed soils. 1-1 2 -SUMMARY AND CONCLUSIONS Some amount of slope instability will be generated in the Watana and Devil Canyon Reservoirs due to reservoir filling. These areas will primarily be in locations where the water level will be at an intermediate level relative to the valley depth. Slope failure will be more common in the Watana Reservoir due to the existence of permafrost soil throughout the reservoir. The Devil Canyon Reservoir is gen- erally in more stable rock and the relatively thin overburden is unfrozen, in the reach of the river upstream from the dam. Although skin flows, minor slides and beaching will be common in parts of the reservoirs it will present only a visual concern and poses no threat to the pro- ject. Many areas in which sliding does occur will stabilize into beaches with a steep backslope. Tree root systems left from reservoir clearing will tend to hold shallow surface slides and in cases where permafrost exists, may have a stabilizing influence since this mat will hold the soil in place until excess pore pressures have dissipated. 2-1 3 -METHODOLOGY The potential for instability of the slopes adjacent to both reservoirs after impoundment was evaluated principally by the use of color aerial photographs at a scale of 1:24,000, color infrared photographs at a scale of 1:120,000 and a brief field reconnaissance. Current slope instability as evidenced by flows and slides, their aspect and slope angle, and the distribution of permafrost was delineated. This information in addition to the soil and rock conditions throughout the reservoirs (R&M Subtask 5.02) and the upper and lower reservoir limits were used in identifying the potential types and zones of instability or beaching as a direct affect of the impounding of the reservoirs. For the Watana Reservoir, the limits used were 2185 feet for the normal pool level and 2015 feet for the minimum reservoir level assuming the normal pool level could be dropped as low as 2115 feet. For the Devil Canyon Reservoir, the limit used was 1450 feet for the normal pool level. Only one level was evaluated because the seasonal drawdown in this reservoir will be minimal. 3-1 4 -SLOPE STABILITY Aside from the formation of beaches due to erosion, slope instability along the reservoir slopes can be generated for two principal reasons: a change in the ground water regime and the thawing of permafrost. Beach erosion can give rise to general instability through the sloughing or failure of an oversteeped back- slope, enlarging the beach area. This is discussed further in Section 5. When a reservoir is filled the ground water table reestablishes itself to a new level around the reservoir rim. This change and the submergence of slopes may cause the slope to be less stable than they were previously. Since most slopes on incised valleys lie very close to equilibrium, forces which lessen the sta- bility of a slope generally could result in instability and failure. Certain conditions could also exist upon filling which would enhance the stability of a slope. An example of this condition is the decrease in the gradient across a jointed rock slope. Drawdown of the reservoir over a short period of time invariably results in in- stability of susceptible slopes. All of these conditions will be addressed in greater detail in this section. 4.1 -Changes-in-Ground Water Regime When the reservoir rises to its maximum level the ground water table in the ad- jacent slope also rises as shown in Figure 4.1. The result is that a slope which, although previously stable and above the ground water table, can now be unstable since it is affected by the pore pressures and seepage forces existing because of nigher ground water table. The slope shown in Figure 4.1 whether it is soil or rock is less stable than it was prior to the existence of the reser- voir. This is not to say that this slope will necessarily fail since failure is dependent on the strength parameters on the soil or the strength along weakness planes in the rock. The potential for failure of such a slope could extend below the water level depending on the slope configuration and the magnitude of the driving force associated with the unsubmerged portion of the slope above the water table. The case of the newly submerged slope just below the reservoir level was exa- mined as an infinite slope in three conditions in which it will exist. These are shown in Figures 4.2 through 4.4. The first case is the original slope, above the water table. The second is the submerged case and the third is the condition just above the reservoir level. The third case could also exist following stabilization of the ground water regime above the reservoir or following a drawdown. Figures 4.2 and 4.3 indicate that the unsubmerged dry slope and the submerged slope have identical factors of safety. Hence, there is no instability caused purely by submergence of a slope. However Figure 4.4 indicates that for the case of seepage parallel to the slope the factor of safety could be reduced by approximately 50 percent. Therefore, instability can be induced by raising the ground water table similar to Figure 4.1 or by drawdown of the reservoir. 4-l Figure 4.5 indicates that a material which has some cohesion is more stable in the submerged condition and although the case with steady seepage parallel to the slope is less stable tnan the drained slope due to the introduction of the seepage forces, the degree of instability is not as great as in a cohesionless material. Figure 4.6 shows that a rock slope which is in equilibrium above the present river would be more stable due to submergence. However, presently drained slopes at higher elevations which are in equilibrium could become less stable due to the reestablishment of a new ground water regime above the reservoir level. There exists only one condition, not addressed in these examples, in which submergence alone causes instability. In this case large block failure could occur when a flatter submerged slope buttresses a steeper slope above the reservoir level. The steeper block is dependent on the lower, flatter lying block for stability. Submergence reduces the sliding resistance of the lower block and although it also reduces the driving force associated with the lower block, it does not reduce the driving force associated with the upper block. 4.2 -Permafrost Thaw The thawing of permafrost follows the example shown in Figure 4.7, taken from W.G. Brown and, G.H. Johnston (1978). The instability of thawing permafrost slopes is addressed by McRoberts and Morgenstern (1974). They indicate that a characteristic feature of both soli- fluction slopes, skin flows, and the lobes of bimodal flows is instability on low angle slopes. The infinite slope analysis previously discussed is appropriate for long shallow slopes. Figure 4.7 shows a section in a thawing slope. Given that: where d = depth of thaw ex: = a constant t = time The depth of thaw is therefore proportional to the square root of time as shown in the previous formulation. In terms of the thaw consolidation ratio, R. R = cx:/2 v'C v where Cv =the coefficient of consolidation. The pressure, u has been found to be: u = yb d/(1 + l/2R2) 4-2 where yd is the effective stress after complete dissipation of the excess pore pressures. Referring to Figure 4.8 on plane AA 1 u = yw Dease + yb Dease (1 /_1_ \ 2R 2 ) The factor of safety Fs is therefore: Fs = ___r__E. (1 _ 1 ) tan ¢ y + . 1 + 1 tan e 2R 2 If no thaw occurs and therefore no excess pore pressure exists this reduces to: vb tan cp Fs = ..L::.. -y tan e which is the same condition as shown in the previous section. The stability of a thawing slope is ultimately dependent primarily on the geotechnical parameters c: ¢ and Cv since the thermal conditions can be determined independently. The excess pore pressures generated during thaw give rise to shallow slides on rela- tively flat slopes. 4.3 -Stability During Earthquakes There are certain conditions which can exist after reservoir filling which will cause slides to occur during earthquakes. This section will address only those situations in which slopes are more susceptible to sliding than in their present condition. Submerged slopes in fine grained sands or with layers of fine grained sands may be susceptible to liquifaction during earthquakes. This is one example of a case where small slides could occur below the reservoir level. In addition, areas above the reservoir rim in which the ground water table has reestablished itself could have a greater potential for sliding during earthquakes with or without liquifaction. Thawing permafrost generates excess pore pressures. In cases where this situa- tion exists in liquifaction susceptible soils, the potential exists for small slides on flat lying slopes. The existence of fine grained sands, coarse silts and other liquifaction suscep- tible materials are not extensive in the reservoir areas. Therefore, it is con- sidered that the extent of liquifaction failures during earthquakes will be small and primarily limited to areas of permafrost thaw. Some slides could occur above the reservoir level in previously unfrozen soils due to the earth- quakes shaking. 4-3 NEW GROUND WATER TABLE _CD SURFACE RESERVOIR LEVEL ORIGINAL GROUND WATER TABLE RIVER POTENTIAL FAILURE SURFACE RIVER 0 500 1000 FEET SCALE TYPICAL SLOPE FAILURE FIGURE 4.1 ~ w F.S.= tan¢ tan e DRY COHESIONLESS SOIL FOR SHEAR STRENGTH FULLY MOBILIZED T = N tan¢ F.S. = 1.0 DEFINITION OF TERMS; e : ANGLE OF THE SLOPE W = WEIGHT OF THE SOIL MASS N : NORMAL FORCE ACTING ON THE SLIDING PLANE T : SHEAR FORCE ACTING ALONG THE SLIDING PLANE f/J : ANGLE OF INTERNAL FRICTION OF THE SOIL F.S. = FACTOR OF SAFETY SLOPE CONDITIONS IN A DRY COHESIONLESS SOIL FIGURE 4.2 RESERVOIR LEVEL SUBMERGED COHESION LESS N = adyb cos e T=adybsine ;; = Yb d cos 2 e r= Yb d cose sine SOIL IF FULL RESISTANCE IS MOBILIZED T = iT tan 0 tan,; THEN F.S. = ~ = 1.0 DEFINITION OF TERMS: e = ANGLE OF THE SLOPE W : WEIGHT OF SOIL MASS )l;b = BOUYANT UNIT WEIGHT OF THE SUBMERGED SOIL ¢ : ANGLE OF INTERNAL FRICTION OF THE SOIL F.S.= FACTOR OF SAFETY SUBMERGED SLOPE CONDITIONS IN A COHESIONLESS SOIL FIGURE 4.3 i, = Lsine L =sine N = )bad cose T = )b a d sine + Yw a d sine = Yt ad sine F.s = N tan¢ . . T DEFINITION OF TERMS: l. : HYDRAULIC GRADIENT ACROSS THE SOIL ELEMENT e : ANGLE OF SLOPE Yb: BOUYANT UNIT WEIGHT OF THE SOIL Yw: UNIT WEIGHT OF WATER )t = TOTAL UNIT WEIGHT OF SOIL 9J : ANGLE OF INTERNAL FRICTION OF THE SOIL F.S.: FACTOR OF SAFETY )bad cose tan~ = )'to d sine = ib tan~ ;; tan e SLOPE CONDITIONS, SEEPAGE PARALLEL TO SLOPE IN COHESIONLESS SOIL FIGURE 4.4 DRY SLOPE c +;. tan.0' F.S. = T SUBMERGED SLOPE c + a-ton0' F.S.= T = = c + Yt Hcos 2 e tan0' X H sine cose c + lb H cos 2 e tani' Yt, H sine cose SEEPAGE PARALLEL TO SLOPE F S = c +;;: tan0' = c + lb H cos 2 tan 0' · · T )tHsinecose THE ABOVE EQUATIONS INDICATE THAT: 1.) THE SUBMERGED CASE IS MORE STABLE THAN THE DRY CASE. 2.) SEEPAGE PARALLEL TO THE SLOPE CASE IS LESS STABLE THAN THE DRY CASE. DEFINITION OF TERMS FS." FACTOR OF SAFETY c " COHESION OF THE SOIL f1 : ANGLE OF INTERNAL FRICTION OF SOIL 9 = ANGLE OF THE SLOPE Yt = TOTAL UNIT WEIGHT OF SOIL )b = BOUYANT UNIT WEIGHT OF SOIL SLOPE CONDITIONS IN A COHESIVE SOIL FIGURE 4.5 /TENSION CRACK ------, SEEPAGE PRESSURE CASE F.S. = cA + ( W cose-U-Vsine) tan ij Wsin e + Vcose SUBMERGED CASE ~A+ ( Wcose) tan 0' F.S. = Wsin e THE ABOVE EQUATIONS INDICATE THE SUBMERGED CASE IS MORE STABLE. DEFINITION OF TERMS: c : COHESION OF THE ROCK MASS W : WEIGHT OF THE ROCK WEDGE U : UPLIFT PRESSURE ON THE ROCK WEDGE V : DRIVING FORCE OF THE WATER BEHIND THE ROCK WEDGE 9 : ANGLE OF THE FAILURE PLANE {i : ANGLE OF INTERNAL FRICTION OF THE ROCK W : WEIGHT OF SUBMERGED ROCK WEDGE A = FAILURE PLANE AREA SLOPE CONDITIONS IN ROCK FIGURE 4.6 THAW EQUATION: L = )d ~~~ Lt = (57)c~~)( 144) = 2052 BTU/FT.3 Cu= )d(O.I7+ I~O) = 57(0.17 + 16%) =32.5 BTU/FT.3 °F --'12 2 ku( T...,-lf) t D = ( 1-a) L ~+~ ~· +'("") < r.-r,j ---- ~ 2 ( 0.8 )( 39-32) t D = [ ( 32 · 5 + 62 4 (0 I)) l < 1-0.1 )(2052) L_+ 2 205 ~ · < 39-32 J ...___ - D = 0.075 VT DEFINITION OF TERMS: D = THAW DEPTH ku: THERMAL CONDUCTIVITY OF THAWED SOIL, USE 0.8 BTU/HR., °F, FT. Tw = WATER TEMPERATURE AT GROUND SURFACE, USE 39° F Tf " TEMPERATURE AT WHICH WATER WILL FREEZE, USE 32° F t = TIME Yw= UNIT WEIGHT OF WATER, USE 62.4 LB./FT.3 a : PERCENT ICE BY VOLUME, USE 0.10 w· L : QUANTITY OF HEAT REQUIRED TO MELT ICE IN I CUBIC FOOT OF SOIL, = )'d IO~ lf )d = DRY UNIT WEIGHT OF SOIL, USE 57 LBS./FT.3 Wj : PERCENT ICE CONTENT, USE 25 Lf = LATENT HEAT, USE 144 BTU/LB. cu: VOLUMETRIC HEAT CAPACITY : )'d (0.17 + .."!!..-) 100 w: PERCENT WATER CONTENT, USE 40 MODEL FOR THAWING OF PERMAFROST FIGURE 4.7 ON PLANE AA' PORE PRESSURE u = Yw 0 cose ... yb 0 cose (Tfr-) 2R2 EFFECTIVE STRESS=)'; Ocose-YwOcose -)bOcose (-1-1 ) 1+-2R2 F.S. = .lJL(I-Yt WHERE DEFINITION OF TERMS: F.S.= FACTOR OF SAFETY Yw = UNIT WEIGHT OF WATER )b : BOUYANT UNIT WEIGHT OF SOIL X= TOTAL UNIT WEIGHT OF SOIL e : ANGLE OF THE SLOPE I ) tan121 1 + I tone ""2R2 o< R = 2 '/"Cv ~ = ANGLE OF INTERNAL FRICTION OF TH~ SOIL R : THAW-CONSOLIDATION RATIO 0< = THAW-CONSOLIDATION CONSTANT Cv: COEFFICIENT OF CONSOLIDATION CONDITIONS IN A THAWING SLOPE Fl GURE 4.8 5 -RESERVOIR GEOLOGY 5.1 -Watana Preliminary reconnaissance mapping of the Watana Reservoir was performed during this study. Principal rock types and general types of surficial material were identified. The topography of the Watana Reservoir and adjacent slopes is characterized by narrow V-shaped stream-cut valley superimposed on a broad U-shaped glacial valley. Surficial deposits mask much of the bedrock in the areas, especially in the lower and uppermost reaches of the reservoir. A surficial geology map of the reservoir, prepared by the COE, distinguishes till, lacustrine and alluvial deposits, as well as general rock types (U.S. COE, 1979). (a) Surficial Deposits Generally, the lower section of the Watana Reservoir and adjacent slopes are predominately covered by a veneer of glacial till and lacustrine de- posits. Two main types of till have been identified in the areas; ablation and basal tills. The basal till is predominately overconsolidated, has a fine grained matrix (more silt and clay) and has a low permeability. Tne ablation till has less fines and a somewhat higher permeability. Lacus- trine deposits consist primarily of poorly graded fine sands and silts with lesser amounts of gravel and clay that exhibit a crude stratification. On the south side of the Susitna River, the Fog Lake area is characteristic of a fluted ground moraine surface. Upstream in the Watana Creek area, glaciolacustrine material forms a broad, flat plain which mantles the un- derlying glacial till and the semiconsolidated Tertiary sediments. Signif- icant alluvial deposits exist in the river valley and consist of reworked outwash and alluvium. Glaciation of the area was accompanied by the fill- ing in of the Susitna River valley. Subsequent modification by alluvial processes during deglaciation resulted in the formation of floodlain ter- races. Ice disintegration features such as kames and eskers have been ob- served adjacent to the river valley. Permafrost exists in the area, as evidences by ground ice, nonsorted poly- gons, stone nets and slumping of the glacial till overlaying permafrost. Numerous slumps have been identified in the Watana Reservoir area, espe- cially in sediments comprised of basal till. This subject will be addressed in more detail in the subsequent section. (b) Bedrock Geology The Watana damsite is underlain by a diorite pluton. Approximately three miles upstream of the Watana damsite, a non-conformable contact between argillite and the dioritic pluton crosses the Susitna River. 5-l (c) ( An approximate location of this contact has also been delineated on Fog Creek, 4 miles to the south of the dam sit e. Just downstream of the con- fluence of Watana Creek and the Susitna River, the bedrock consists of semiconsolidated, Tertiary, sedimentary rocks (Smith 1974) and volcanics of Triassic age. These Triassic volcanics consist of metavolcaniclastic rocks and marble (Csejtey, et. al. 1978). From just upstream of Watana Creek to Jay Creek, the rock unit consists of a metavolcanogenic sequence dominantly composed of metmorphosed flows and tuffs of basaltic to andesitic composi- tion. From Jay Creek to just downstream of the Oshetna River, the reser- voir is underlain by a metamorphic terrain of amphibolite and minor amounts of greenschist and foliated diorite. To the east of the Oshetna River, glacial deposits predominate. The main structural feature of the Watana Reservoir is a thrust fault, which trends northeast-southwest and is known as the Talkeetna Thrust (Csejtey, et. al. 1980). This thrust fault crosses the Susitna River approximately 8 miles upstream of the Watana damsite. The dip of this fault is uncertain as Csejtey and others (1980) have interpreted it to have a southeast dip, while Turner and Smith (1974) suggest a northwest dip. To date, no evidence has been found for recent displacement along this fault. At the southwest end of the fault, unfaulted Tertiary volcanics overlie the fault (Csejtey, et. al. 1980). Evidence of possible faulting has been ob- served in the sedimentary and volcanic rock of Jurassic age, north of Watana Creek (Csejtey, et. al. 1980; Turner & Smith, 1Y74). Investigations of the Tertiary sediments in Watana Creek by members of the University of Alaska Geology Department did not however, uncover any direct evidence of faulting. Slope Stability and Erosion The geology of the slopes underlying and adjacent to the reservoir consist primarily of unconsolidated material. Current or previous slope instabil- ity on the slopes above the Susitna River, as defined by aerial photogra- phic interpretation and some field reconnaissance indicate that the types of mass movement consist primarily of solifluction, skin flows, bimodal flows, and small rotational slides. These types of movement occur predomi- nately in basal till or in areas where the basal till is overlain by lacus- trine deposits (Table 5.1). In addition, solifluction which originated in the basal till has proceeded downslope over some of the floodplain ter- races. Aspect, and therefore incoming solar radiation, is not a key factor as all slopes are susceptible to mass movement. In Figures 5.3 through 5.18, the distribution of permafrost has been delineated primarily on the flatter slopes and does not include its delineation outside the 2300 foot contours. These areas are potentially underlain by permafrost. Inclined slopes may be underlain by permafrost, but based on photogramrnetric charac- teristics, the active layer is much thicker, permafrost soils are thawing and/or permafrost doesn't exist. As a generalization, the distribution of permafrost is nearly continuous in the basal till and is scattered contin- uously in the lacustrine deposits. Three major factors will contribute significantly to slope instability in the Watana Reservoir. These are the changes in the ground water regime, the large seasonal fluctuation of the reservoir level (est. at 60 feet) and the thawing of permafrost. The Devil Canyon Reservoir will be primarily affected by the first and to a lesser extent by the second factor. These . factors were analyzed for their effects on typical conditons in the reser- voir and from this, four basic models of shoreline conditions were devel- oped (Figures 5.1 and 5.2). The two processes affecting the shoreline of the reservoirs are beaching and slope stability. These models were applied to selected reaches of the reservoir shoreline and evaluated for conditions at or near normal pool level (Figures 5.3 through 5. 18). It should be noted that the slope stability of the Watana Reservoir was evaluated for the worse case, as two reservoir levels were considered for their potential effect on their slopes. In cases where sliding will occur it will not be uncommon for some flows or possibly beaching to occur over the same reach. Slope instability during and after reservoir impounding will be addressed. below. The filling of the reservoir to the normal pool level is estimated to take approximately three years. Uue to the rate of impounding, the potential for slope instability occuring during the flooding of the reservoir will be minimal and confined to shallow surface flows and possibly some sliding. These slopes will be more susceptible to slope instability after impounaing when thawing of the permafrost soils will occur and the ground water regime has reestablished itself in the unfrozen soils. Near the damsite, assuming that the current contours will remain unchanged, the north abutment will have the potential for beaching except for possibly some small flows and slides adjacent to Deadman Creek. On the south abut- ment, thawing of the frozen basal tills will result in numerous skin and bimodal flows and there will be a potential for small rotational sliding to occur primarily opposite Deadman Creek. On the south abutment between the Watana damsite and Vee Canyon the shore- line of the reservoir is susceptible to a high potential for flows and shallow rotational slides (Figures 5.19 and 5.20). In contrast to the north abutment, the shoreline is almost exclusively in contact with frozen basal tills, overburden is relatively thick and steeper slopes are present. Thermal erosion, resulting in the erosion and thawing of the ice-rich fine grained soils will be the key factor influencing their stability. In the Watana Creek drainage area there is a thick sequence of lacustrine material overlying the basal till (Figure 5.21). Unlike the till, it appears that the lacustrine material is largely unfrozen. All four models are perceived to have the potential for occurring here, depending on where the seasonal drawdown zone is in contact with the aforementioned stratigraphy. Overall, the north abutment in contrast with the south abutment, doesn't have the constant steep slopes and the slopes are slightly better drained, which may be indicative of less continuous permafrost and/or slightly coarse material at the surface with a deeper active layer. In general, the potential for beaching is higher because the seasonal drawdown zone will be in contact with a thin veneer of colluvium over bedrock and in a number of areas, low slopes (Figure 5.22). In the Oshetna-Goose Creeks area there is a thick sequence of lacustrine material. Permafrost appears to be nearly 5-3 continuous in this area based on the presence of unsorted polygonal soils and potential thermokarst activity around some of the many small ponds (thaw lakes/kettles). The reservoir will be primarily confined within the floodplain and therefore little modification of the slopes is expected. Where the slopes are steep, there could be some thermal-niche erosion re- sulting in small rotational slides. The potential for a large slide occurring and generating a wave with the likelihood of overtopping the dam is ultimately remote. For this condition to occur, a very high, steep slope with a potentially unstable block of large volume would need to exist adjacent to the reservoir. In approxi- mately the first 16 miles upstream of the dam, the shoreline will be in contact with the low slopes of the broad U-shaped valley, above the present river valley. The only areas where these conditions are met is in the zone approximately between 16 and 30 miles upstream of the dam. In this area, no potentially large landslides were observed photogrammetrically. Beyond 30 miles upstream, the reservoir begins to meander and narrows, therefore any wave induced by a large landslide would in all likelihood have a tendency to dissipate prior to reaching the dam. In general the following conclusions can be drawn about the slope condi- tions of the Watana Reservoir after impounding: -the principal factors influencing slope instability are the large season- al drawdown of the reservoir and the thawing of permafrost soils. Other factors are the change in the ground water regime, the steepness of the slopes, coarseness of the material, thermal toe erosion, and the fetch available to generate wave action; -the potential for beaching will occur primarily on the north abutment of the reservoir; a large portion of the reservoir slopes are susceptible to shallow slides, mainly skin and bimodal flows, and shallow rotational slides; -the potential for a large block slide which might generate a wave that could overtop the dam is remote; and -the period in which restabilization of the slopes adjacent to tne reser- voir will occur is largely unknown. Generally speaking, reservoir slopes which are totally submerged, or in which the filling is above the break in slope will exhibit less stability problems than those in which the reservoir is at an intermediate or low level. Flow slides induced by permafrost thaw in fine grained soil can, however, occur on very flat lying slopes. 5.2 -Devil Canyon (a) Surficial and Bedrock Geology The topography in and around the Devil Canyon Reservoir is bedrock con- trolled. Overburden is thin to absent, except in the upper reaches of the 5-4 proposed reservoir where alluvial deposits cover the valley floor. A large intrusive plutonic body underlies most of the reservoir and adja- cent slopes. It is perdominantly a biotite granodiorite with local areas of quartz diorite and diorite. It is light gray to pink, medium grained and composed of quartz, feldspar, biotite and hornblende. The most common mafic mineral is biotite. When weathered, the rock has a light yellow-gray or pinkish yellow-gray color, except where it is highly oxidized and iron stained. The granodiorite is generally massive, competent, and hard with the exception of the rock exposed on the upland north of the Susitna River where the biotite granodiorite has been badly decomposed as a result of physical weathering. The other principal rock types in the reservoir area are argillite and graywacke, which are exposed at the Devil Canyon damsite. In summary, the argillite has been intruded by the massive granodiorite and as a result, large isolated roof pendants of the argillite and graywacke are found locally throughout the reservoir and surrounding areas. The argillite/ graywacke varies to a phyllite of low metamorphic grade, with possible iso- lated schist outcrops. The rock has been isoclinally folded into steeply dipping structures which generally strike northeast-southwest. The contact between the argillite and the biotite granodiorite crosses the Susitna River just upstream of the Devil Canyon damsite. It is nonconformable and characterized by an almost aphanitic texture with an apparent wide chilled zone. The trend of the contact is roughly northeast-southwest as it crosses the river. Several large outcrop areas of the argillite which are completely surrounded by the biotite granodiorite are located in the Devil Creek area. Preliminary joint measurements made in the reservoir area indicate struc- tural trends similar to those encountered at the damsite. Joint spacing at these stations ranged up to 3 feet. (b) Slope Stability and Erosion The Devil Canyon Reservoir will be entirely confined within the walls of the present river valley. This reservoir will be characterized by a narrow deep water body which will be subject to only minimal seasonal drawdown. Much of the topography of this reservoir is bedrock controlled. In the vicinity of Devil Creek downstream to the damsite, the slopes of the reser- voir and its shoreline consists primarily of bedrock and bedrock with a thin veneer of colluvium or till. Upstream of Devil Creek, the slopes of the reservoir are comprised of increasing amounts of unconsolidated materials, especially on the south abutment between river mile 166 and 178. These materials are composed of basal till and coarse grained floodplain and alluvial fan deposits. Current or previous slope instability on the slopes above the Susitna River as defined by photogrammetry and limited field reconnaissance, indicate that the types of mass movement present are skin and bimodal flows, a potential block slide in rock and one large rotational slide. The basal 5-5 tills are the primary materials susceptible to mass movement. As in the Watana Reservoir, aspect is not a key factor in delineating which slopes are more susceptible to mass movement. As a generalization, permafrost is largely absent downstream of approximately river mile 166, except for the higher elevations above the river where solifluction activity is wiaely scattered. Over this reach, on the south abutment and south of the dam site there is a possibility of sporadic permafrost existing within the delineated areas but it is generally thought to be unlikely. Upstream of this area, the basal till is nearly continuously frozen as evidenced by field information along the access road corridors and in Borrow Area "W. Downstream of the Devil Creek area, instability is largely reserved to small rock falls. Beaching will be the primary process activity upon the shoreline in this area (Figures 5.23 through 5.33). Although this area is mapped as a basal till, it is coarser grained than that which is found in the Watana Reservoir and therefore is more susceptible to beaching. In areas where the shoreline is in contact with steep bedrock cliffs, the fluctuation of the reservoir will contribute to rock falls. Fluctuation of the reservoir and therefore the ground water table, accompanied by seasonal freezing and thawing will encourage frost riving as an erosive agent to accelerate degradation of the slope and beaching. These rock falls will in no way have the capacity to produce a large wave which might eventually affect the dam. In Devil Creek, a potential small block slide may exist but it now appears stable and will have no effect on the reservoir. Beyond Devil Creek, beaching will also be the common erosive agent up to river mile 175. Heyond river mile 167 the reservoir will be primarily confined to the river floodplain. Present slope stability above reservoir normal pool level will continue to occur, with primary beaching occurring at the shoreline. At river mile 175 there is a possibility that an old large landslide on the south abutment, which has been stable for quite some time, may become unstable after reservoir impounding. This landslide has a large arcuate back scarp which has become completely vegetated since its last movement. This landslide which has a volume of approximately 3.4 million cubic yards, has the potential for sliding due to either thermal erosion or changes in the ground water regime (Figure 5.34). This large rotational slide is composed of basal till which is for the most part frozen. A large bimodal flow exists within this block and is headed by a large body of ground ice. Each year, ablation of the ice results in flowage of saturated material downslope. The distance from the dam, the meandering of the river valley and the shallow depth of the reservoir indicate that the potential of a wave induced by a possible slide, affecting the dam is remote. Pre- liminary assessment of a mass slide in this area suggests that blockage of the river flow that would affect the upstream river level would be only a temporary condition until the river was able to erode through the flow. It is likely that the intial sliding in this area was activated by erosion. Although this will not be a factor after filling the reservoir, the sub- mergence of the lower slope could endanger this old slide mass. 5-6 J In general the following conclusions can be drawn about the slope condi- tions of the Devil Canyon Reservoir after impounding: minimal drawdown of the reservoir is conducive to stable slope condi- tions -the lack of unconsolidated materials along the lower slopes of the reser- voir and the existence of stable bedrock conditions are indicative of stable slope conditions after reservoir impounding -an old large landslide in the upper reservoir has the potential for in- stability, this could conceivably create problems by blocking reservoir flow to Devil Canyon for a short period of time. -the probability of a wave overtopping the dam is remote. 5-7 ------- UNIT Bedrock Colluvium, over bedrock & b~drock exposures Floodplain Floodplain Terraces Granular Alluvial Fan Kame Deposits Lacustrine Bas a 1 Ti 11 Ab 1 at ion Ti 11 Ablation Ti 11 over Unweathered Bedrock Basal Ti 11 over Unweathered Bedrock Lacustrine over Basal Ti 11 TERRAIN UNIT SYMBOL Bxu c + Bxu Bx u Fp Fpt Ffg GFK L Gt b-f Gt a Gta 1iXU Gtb-f "i3XlJ L Gtb-f TABLE 5.1: CHARACTERISTICS OF SLOPE MATERIALS --------------SLOPE CONDITlONs-·-~ PERM/\FROS T CIIRRENT SLOPE ______ MA_T_ER_!_~_L ___ --"--"~ "_"_CO_NQ_l_!_I_O_NS_l ____ __c_S_:_:T A-'-_8 I LI TY Consolidated bedrock. unfrozen stable Angular blocks of rock with some sand and silt overlying bedrock. Rounded cobbles, gravel and sand, sorted and layered with or without silt cover. Rounded cobbles, gravel and sand with some silt covered by thin silt layers. Sorted, layered. Rounded cobbles, gravel, with sand and some silt. Some sorting and layering of materials. Rounded and striated cobbles, and sand. Crudely sorted and layered. Fine sand to sandy silt with occas- sional pebbles. Sorted and layered. Gravelly silty sand and gravelly, sandy silt cobbles and boulders poorly rounded and striated. No layering, poorly graded. Rounded and striated cobbles, gravel and sand, no layering, well graded. Boulder cobble, lag covers surface. Rounded and striated cobbles, gravel and sand, no 1 ayer i ng we 11 gr· aded over bedrock. Gravel, silty sand and sandy si 1t with no layering or sorting over berl- •·ock. Poorly graded si 1 ty sand anrl s<Jndy silt overlying basal till. unfrozen unfrozen unfrozen unfrozen unfrozen unfrozen frozen frozen unfrozen frozen unfrozen frozen L spar· ad i c Gtb frozen s t ah I e stable stable stable stab 1 e stable stable unstable stable stable stable stable unstable AFTER RESERVOIR FILLING2 --Tow---pEP----~~ Beach i ng ( I ) 3, 4 BPilching (I) Beaching Beaching (I) Beaching (I) Beaching (I) lle~ching (I) Flows (II) Flows (II) Beach i ng ( I ) F 1 ows (I I) !leach i nq (I) Flows (II) Flows (I I I) Sliding (III) Sliding(IV) Sliding (IV) S 1 i ding (IV) S 1 i ding ( IV) Slumping (IV) ---L--------------------------"·--"-"-------"---------------------L----"-----'---"-"----- FOOTtlOTES: 1 2 3 4 As perceived to be in roost case-;. Beaching vs mass movernent over certain reaches of reservoir; where slidinq occurs, can expect sorne potential beaching and flows. Potential of frost riving on rock slopes resulting in rockfall. Nurnerical values apply to slope rnorlels, see F1qures 5.1 anrl 5.2. BEACHING(I)BEACHING(I)MINORINITIALLYAFTERSEVERALYEARS.....ASSUMPTIONS:FLATSLOPES.COARSEGRAINEDDEPOSITSORUNFROZENTILLANDLACUSTRINEDEPOSITS•STEEPBEDROCKSLOPES.FLUCTUATIONOFRESERVOIRANDGROUNDWATERTABLECAUSESFROSTWEDGINGTOOCCURCAUSINGROCKFALL.FLOWStrr)FLATSLOPES.GENERALLYFINEGRAINEDDEPOSITS,FROZEN.SLOPEANDMODELSFORDEVILCANYONTHEWATANARESERVOIRSFIGURE5.1 INITIALLYAFTERSEVERALYEARSASSUMPTIONS:SLIDING(JII)STEEPSLOPES.TWOLAYERCASE,LOWERLAYERISFINEGRAINEDANDFROZEN.UPPERLAYERISCOARSERGRAINED,PARTLYTOCOMPLETELYFROZEN.FLOWSINLOWERLAYERACCOMPANYSLOPEDEGRADATIONSLIDING(IT)STEEPSLOPES.FINEGRAINEDANDUNFROZEN.(H)STEEPSLOPES.FINEGRAINEDAND1!J$lFROZEN.NOTE:POSSIBLEFURTHERSLIDINGIFTHAWBULBEXTENDSINTOSLOPEWITHTIME.THEWATANARESERVOIRSMODELSFORCANYONSLOPEANDDEVILFIGURE5.2 FIGURE 5 .15 FIGURE 5.1 4 FIGURE 5. 18 FIGURE 5.16 "'' II FIGURE 5 .13 FIGURE 5 ·12 WATANA RESERVOIR INDEX MAP FIGURE 5 ·10 FIGURE 5 .9 LOCATION MAP F IGURE 5 · 5 8 MILES SCALE: 0~~§4 iiiiiiiiiii_,. LEGEND ---NORMAL MAXIMUM ----OPERATING LEVEL 2185' CONTOURS ARE IN ~2300 -FEET ABOVE MSL FIGURE 5 ·4 FIGURE 5.3 WATANA SLOPE STABILITY MAP J / D AREAS OF c TYPES OF SLOPE I li BEACHING URRENT SLOPE INSTABILIT Y INSTABILITY : lli FLOWS :N: SLIDING (UN SLIDING ( p FROZEN) I II DENOTES A~~~AFROST) I (17) PRIMARY BEAC EXTENT AND TYPE I. JI POTENTIAL SLI~i::C,G INSTAB ILITY W OF INSTABILITY ---BEACHING AND F ITH SOME _ -NORMAL LOWS POSSIBLE -~--NORMAL :~N~~~: OPERATING L~V~~FINED AREA A A RIVER MILES OPERATING LEVEL t J SECTION LOCATION D AREA OFP NOTES OTENTIAL PER MAFROST I. REFER TO F IGU DESCRIPTION OFRES 5,1 AND 5 2 2. NO DELINEA TYPE OF SLOPE ~~;TADETAILED 2 3 TION OF BILITY M 00 FEET PERMAFROS ODELS 3 T AREA ABO . ~~E:S OF POTENTIAL VE ELEVATION FUT IR PHOTO INTE PERMAFROST URE VER I FI C AT I ~~RETATION AND B~~LED PRINCIPALLY L REQUIRE SCALE ---------~F~IGiUUIRE 5_4 / l \ L' ~) IT ) (u (: I lit ,,l40.()( -r ) .,) (> ~ / / '"" ,.r ~ "''.<•; '<>)~-; / l I ~I " trr l,i:.O.OOO ~ I O.lt O! l't.o!(:•'•'"' l 1000' C..t-~~>••·~ ;()()' WATANA SLOPE STABILITY MAP /( '-I-Til ,, I "' () f ' '""'· lj't\ ':C. ~,\ /'\ -t~ __.., ,, " + / / , I r r "1 D AREAS OF CURRENT SLOPE INSTABILITY TYPES OF SLOPE INSTABILITY: I BEACHING li FLOWS m SLIDING (UNFROZEN) ]J[ SLIDING (PERMAFROST) III DENOTES AREA EXTENT AND TYPE OF INSTABILITY I (]J[) PRIMARY BEACHING INSTABILITY WITH SOME POTENTIAL SLIDING I -li BEACHING AND FLOWS POSSIBLE IN DEFINED AREA NORMAL MAXIMUM OPERATING LEVEL -----NORMAL MINIMUM OPERATING LEVEL A A t J SECTION LOCATION D AREA OF POTENTIAL PERMAFROST REFER TO FIGURES 5 .1 AND 5 .2 FOR DETAILED DESCRIPTION OF TYPE OF SLOPE INSTABILITY MODELS 2. NO DELINEATION OF PERMAFROST AREA ABOVE ELEVATION 2300 FEET 3. AREAS OF POTENTIAL PERMAFROST BASED PRINCIPALLY ON AIR PHOTO INTERPRETATION AND WILL REQUIRE FUTURE VERIFICATION SCALE O~~~IOO~O~iiiiii~20~00 FEET FIGURE 5.5 + •• •000 e..te.. •........ 100' I + SLOPE WATANA STABILITY MAP ~ ' I -1/ I I L·, (• I ~ .1,/' / / D AREAS OF CURRENT SLOPE INSTABILITY TYPES OF SLOPE INSTABILITY: I BEACHING li FLOWS li[ SLIDING (UNFROZEN) Ill: SLIDING (PERMAFROST) III DENOTES AREA EXTENT AND TYPE OF INSTABILITY I (Ill:) PRIMARY BEACHING INSTABILITY WITH SOME POTENTIAL SLIDING I -li BEACHING AND FLOWS POSSIBLE IN DEFINED AREA NORMAL MAXIMUM OPERATING LEVEL -----NORMAL MINIMUM OPERATING LEVEL RIVER MILES A A t .t SECTION LOCATION D AREA OF POTENTIAL PERMAFROST NOTES REFER TO FIGURES 5.1 AND 5.2 FOR DETAILED DESCRIPTION OF TYPE OF SLOPE INSTABILITY MODELS 2. NO DELINEATION OF PERMAFROST AREA ABOVE ELEVATION 2300 FEET 3. AREAS OF POTENTIAL PERMAFROST BASED PRINCIPALLY ON AIR PHOTO INTERPRETATION AND WILL REQUIRE FUTURE VERIFICATION SCALE 0!--~1000~~~2~000. FEET FIGURE 5.6 l / \ ~J v./ \ III-II , ' .. ( " Cou o• ~~~~~·~~•"r , ,g · fl; .St•'• ,-, •CIXi CIW>'O.." l>l>tr•e• 'O"l' < r ) ...-\ \ \ //' J• / / / / r -) WATANA SLOPE STABILITY MAP " v r f • } I / ; ··-__ ,. / r ·\ \ \ / II .1. / ( \' ' I ( --..; D AREAS OF CURRENT SLOPE INSTABILITY TYPES OF SLOPE INSTABILITY: I BEACHING li FLOWS m SLIDING (UNFROZEN) 1ll: SLIDING (PERMAFROST) I II DENOTES AREA EXTENT AND TYPE OF INSTAB ILITY I (Jlr) PRIMARY BEACHING INSTABILITY WITH SOME POTENTIAL SLIDING I -li BEACHING AND FLOWS POSSIBLE IN DEFINED AREA NORMAL MA)(IMUM OPERATING LEVEL -----NORMAL MINIMUM OPERATING LEVEL RIVER MILES A A t J SECTION LOCATION D AREA OF POTENTIAL PERMAFROST I. REFER TO F IGURES 5 .1 AND 5.Z FOR DETAILED DESCRIPTION OF T YPE OF SLOPE I NSTABILITY MODELS 2. NO DELINEATION OF PERMAFROST AREA AB OVE ELEVATION 2300 FEET 3. AREAS OF POTENTIAL PERMAFROST BASED PRINCIPALLY ON AIR PHOTO INTERPRETATION AND WILL REQUIRE FUTURE VER IFI CATI ON 0 1000 2000 FEET SCALE FIGURE 5.7 111 l ,t 1!,000 t hh .. ,...1 • .,...., ., ". k•lt 1000' c--••..-..o~ 000 I-N l • L l' U + SLOPE ,-; .:.../ / - -........... " I WATANA STABILITY MAP / / ,_ J II c::::.::~ I' I' ( D AREAS OF CURRENT SLOPE INSTABILITY TYPES OF SLOPE INSTABILITY : I BEACHING :a: :m: FLOWS SLIDING (UNFROZEN) llZ: SLIDING (PERMAFROST) /I/ DENOTES AREA EXTENT AND TYPE OF INSTABILITY I (lll:) PRIMARY BEACHING INSTABILITY WITH SOME POTENTIAL SLIDING I-ll: BEACHING AND FLOWS POSSIBLE IN DEFINED AREA NORMAL MAXIMUM OPERATING LEVEL -----NORMAL MINIMUM OPERATING LEVEL X RIVER MILES A A t J-SECTION LOCATION D AREA OF POTENTIAL PERMAFROST NOTES 1. REFER TO FIGURES 5 .) AND 5 .2 FOR DETAILED DESCRIPTION OF TYPE OF SLOPE INSTABILITY MODELS 2. NO DELINEATION OF PERMAFROST AREA ABOVE ELEVATION 2300 FEET 3 AREAS OF POTENTIAL PERMAFROST BASED PR IN CIPALLY . ON AIR PHOTO INTERPRETATION AND WILL REQUIRE FUTURE VERIFICATION SCALE o~~~~~ooiiioiiiiiiiiiiiiii2iiiooo FEET FIGURE 5.8 "'3, t6~.ooo II '$.110.000 N 3,2'1'~.000 Oo••ol~'o''"ll"' r •9 '' Sui• 1 • !COO' C"'!o..' llll'"'l>! IC.O' 20' 18 !. ~"1••1•1,1 ~r'-.J + r t / ) r I I-II ( N) WATANA SLOPE STABILITY MAP D AREAS OF CURRENT SLOPE INSTABILITY TYPES OF SLOPE INSTABILITY: I BEACHING li FLOWS m SLIDING I UNFROZEN) llr SLIDING (PERMAFROST) /II CENOTES AREA EXTENT AND TYPE OF INSTABILITY I (llr) PRIMARY BEACHING INSTABILITY WITH SOME POTENTIAL SLIDING I -li BEACHING AND FLOWS POSSIBLE IN DEFINED AREA NORMAL MAXIMUM OPERATING LEVEL -----NORMAL MINIMUM OPERATING LEVEL RIVER MILES A A t 1 SECTION LOCATION NOTES I. REFER TO FIGU RES 5.1 AND 5 .2 FOR DETAILED DESCRIPTION OF TYPE OF SLOPE INSTABILITY MODELS 2. NO DELINEATION OF PERMAFROST AREA ABOVE ELEVATION 2300 FEET 3. AREAS OF POTENTIAL PERMAFROST BASED PRINCIPALLY ON AIR PHOTO INTERPRETATION AND WILL REQUIRE FUTURE VERIFICATION SCALE O~~~IO~O~Oi;;;o;;;;i2;;ii000 FEET FIGURE 5.9 ~ ~ ; ~ H 3,2<110.000 ,.,,t:~.ooo t-- !)olfof~·~~~,.,, 1 !9-lt • 1000" <:o<t·~· ...... Wii «· g ~ WATANA SLOPE STABILITY v I r I / ; / / D AREAS OF CURRENT SLOPE INSTABILITY TYPES OF SLOPE INSTABILITY : I BEACHING li FLOWS m SLIOING (UNFROZEN) ll[ SLIDING (PERMAFROST) I II DENOTES AREA EXTENT AND TYPE OF INSTAB ILITY I (ll[) PRIMARY BEACHING INSTABILITY WITH SOME POTENTIAL SLIDING I -li BEACHING AND FLOWS POSSIBLE IN DEFINED AREA NORMAL MAXIMUM OPERATING LEVEL -----NORMAL MINIMUM OPERATING LEVEL RIVER MILES A A t J-SECTION LOCATION D AREA OF POTENTIAL PERMAFROST NOTES I. REFER TO FIGURES :5.1 AND 5. 2 FOR DETAILED DESCRIPTION OF TY PE OF SLOPE INSTABILITY MODELS 2 . NO DELINEATION OF PERMAFROST AREA ABOVE ELEVATION 2300 FEET 3 . AREAS OF POTENTIAL PERMAFROST BASED PRINCIPALLY ON AIR PHOTO INTERPRETATION AND WILL REQUIRE FUTURE VERIFI CATI ON 0~~~1000~~~2~000. FEET FIGURE 5.10 I I >,l I / ~ ~. l'SO .OOO 0.·· l'llo ;;'""' "c--....... \......,.......__ ''\, ' ---\.::._ \ h~ ' ~ ......_______ - '-, ............. ......_, --."-- --~, -~---::___ ~~ I WATANA SLOPE STABILITY MAP I r LEGEND r---J SLOPE INSTABILITY L___j AREAS OF CURRENT TYPES OF SLOPE INSTABILITY: I li lii ]l[ III I(llZ') I-li , A A t.t D NOTES BEACHING FLOWS SLIDING (UNFROZEN) SLIDING (PERMAFROST) NO TYPE OF INSTABILITY ~~~~::; BAE:E;HI~~T~:;T:BILITY WITH SOME POTENTIAL SLIDING SSIBLE IN DEFINED AREA BEACHING AND FLOWS PO NORMAL MAXIMUM OPERATING c~:~c NORMAL MINIMUM OPERATING RIVER MILES SECTION LOCATION AREA OF POTENTIAL PERMAFROST I REFER TO FIGURES 5.1 AND 5.2 . DESCRIPTION OF TYPE OF SLOPE FOR DETAILED INSTABILITY MODELS 2 . NO DELINEATION OF PERMAFROST AREA ABOVE ELEVATION 2300 FEET BASED PRINCIPALLY 3. AREAS OF POTENTIALP~~~~;;N~~TD WILL REQUIRE ON AIR PHOTO INTER FUTURE VER IFICATION 0 1000 2000 FEET SCALE FIGURE 5.11 I (N) _, f (> I / I I II :rl + 0.11 o! ,.,..,ct••P, r .,. 8• $ctlt •Looo' C••~r ill'""•' 100 WATANA SHf.'f.T!~(X SLOPE STABILITY MAP +-- D AREAS OF CURRENT SLOPE INSTABILITY TYPES OF SLOPE INSTABILITY: I BEACHING :0: FLOWS m SLICING (UNFROZEN) Ill: SLIDING (PERMAFROST) III DENOTES AREA EXTENT AND TYPE OF INSTABILITY I (llr) PRIMARY BEACHING INSTABILITY WITH SOME POTENTIAL SLIDING I-:0: BEACHING AND FLOWS POSSIBLE IN DEFINED AREA NORMAL MAXIMUM OPERATING LEVEL -----NORMAL MINIMUM OPERATING LEVEL X RIVER MILES A A t 1 SECTION LOCATION D AREA OF POTENTIAL PERMAFROST NOTES I. REFER TO FIGURES5.1 AND 5.2 FOR DETAILED DESCRIPTION OF TYPE OF SLOPE INSTABILITY MODELS I 2. NO DELINEATION OF PERMAFROST AREA ABOVE ELEVATION 2300 FEET 3. AREAS OF POTENTIAL PERMAFROST BASED PRINCIPALLY ON AIR PHOTO INTERPRETATION AND WILL REQUIRE FUTURE VERIFICATION SCALE 0-~~~1000~-~2~000 FEET FIGURE 5.12 ···--+- a.tt ., ....... , •• .,., ., ,., et 1000 , ... or.. lfl'•···· 1()0 SLOPE WATANA STABILITY D AREAS OF CURRENT SLOPE INSTABILITY TYPES OF SLOPE INSTABILITY: I BEACHING li FLOWS m SLIDING (UNFROZEN) lll: SLIDING (PERMAFROST) /I/ DENOTES AREA EXTENT AND TYPE OF INSTABILITY I (llr) PRIMARY BEACHING INSTABILITY WITH SOME POTENTIAL SLIDING I -li BEACHING AND FLOWS POSSIBLE IN DEFINED AREA NORMAL MAXIMUM OPERATING LEVEL -----NORMAL MINIMUM OPERATING LEVEL RIVER MILES A A t .t SECTION LOCATION D AREA OF POTENTIAL PERMAFROST NOTES I. REFER TO FIGURES 5.1 AND 5.2 FOR DETAILED DESCRIPTION OF TYPE OF SLOPE INSTABILITY MODELS 2. NO DELINEATION OF PERMAFROST AREA ABOVE ELEVATION 2300 FEET 3. AREAS OF POTENTIAL PERMAFROST BASED PRINCIPALLY ON AIR PHOTO INTERPRETATION AND WILL REQUIRE FUTURE VER I F"I CAT IO N SCALE O~IIIIIIIIII~I~OOOiiiiiiiiiiiiiiiiiiii2iiiiOOO FEET FIGURE 5.13 ·- SLOPE WATANA STABILITY MAP + 11 AREAS OF CURRENT L__j E INSTABILITY : TYPES OF SLOP SLOPE INSTABILITY BEACHING I FLOWS ROZEN ) ][ SLIDING ( U~~MAFROST) PE OF INSTABILITY ~ SLIDING (:REA EXTENT AND ;~ WITH SOME III DENOTES ACHING INSTABILI A I (llr) ~~~~~~~ESLIDING POSSIBLE IN DEFINED ARE BEACHING AND FLOW~PERATING LEVEL I-][ NORMAL MAXIMUM OPERATING LEVEL --==-NORMAL MINIMUM ---; RIVER MILES A A t.t SECTION LOCATION D PERMAFROST AREA OF POTENTIAL NOTES AND 5 .2 FOR DET~ED MODELS RES 5 I IN STABILI REFER TO F I G~ TYPE . OF SLOPE ABOVE ELEVATION DESCRIPTION 0 OF PERMAFROST AREA 2. NO DELINEATION PRINCIPALLY 2300 FEET NTIAL PERMAFROST B~~L~ REQUIRE 3. AREAS OF POT~TERPRETATION AND ON AIR P~~~~F ICAT ION FUTURE SCALE FIGURE 5.14 I -+-I wl --+ Dflt. ,... .......... , '·"··· Sc..ll'f ~·· 1000' ~ "1 ... .,..; l()tj Nltts,OOO + I-N I WATANA SLOPE STABILITY MAP D AREAS OF CURRENT SLOPE INSTABILITY TYPES OF SLOPE INSTABILITY: I BEACHING li FLOWS m SLIDING (UNFROZEN) lll: SLIDING (PERMAFROST) /I/ DENOTES AREA EXTENT AND TYPE OF INSTABILITY I (lll:) PRIMARY BEACHING INSTABILITY WITH SOME POTENTIAL SLIDING I -li BEACHING AND FLOWS POSSIBLE IN DEFINED ARE A NORMAL MAXIMUM OPERATING LEVEL -----NORMAL MINIMUM OPERATING LEVEL X RIVER MILES A A t ! SECTION LOCATION D AREA OF POTENTIAL PERMAFROST NOTES I. REFER TO FIGURES 5 .1 AND 5 . 2 FOR DETAILED DESCRIPTION OF TYPE OF SLOPE INSTABILITY MODELS 2.. NO DELINEATION OF PERMAFROST AREA ABOVE ELEVATION 2300 FEET 3. AREAS OF POTENTIAL PERMAFROST BASED PRINCIPALLY ON AIR PHOTO INTERPRETATION AND WILL REQUIRE FUTURE VERIFICATION SCALE 0 1000 2000 FEET ~~~ FIGURE 5 .15 I (N) L I !_ I ~. + + SLOPE I WATANA STABILITY \. MAP -i-- +- ..... LEGEND SLOPE INSTABILITY AREAS OF CURRENT E ;~; j PE INSTABILITY : TYPES OF SLO BEACHING I FLOWS FROZEN) ! SLIDING ( U~RMAFROST) PE OF INSTABILITY ]l[ SLIDING (:REA EXTENT AND T~ WITH SOME III DENOTES NG INSTABILIT I(l7) ~~~t~J,.~E:L~~~ POSSIBLE IN DEFINED AREA BEACHING AND FLOW~PERATING LEVEL I -li OR MAL MAXIMUM ERATING LEVEL ---:. ~ORMAL MINIMUM OP ·-;-RIVER MILES A A t J-SECTION LOCATION NOT ES OR DETAILED S · ·--5 1 AND 5.2 F TABILITY MODEL I. REFER TO :~~~R~~PE. OF SLOPE INS ABOVE ELEVATION DESCRIPTIO AFROST AREA ION OF PERM 2. NO DELINEAT PRINCIPALLY ::~~:~; POTI~~~~~~~~~~N~~TD B:L~ REQUIRE 3 · ON AIR PHV~~FICATION FUTURE SCALE FIGURE 5.16 + I (:rl) 0 I (:rl) l 0.•• .. ..,..,.,, • .p, • '" ., Ol'l!'loo: ..,.,n' ;(10 WATANA SLOPE STABILITY MAP D AREAS OF CURRENT SLOPE INSTABILITY TYPES OF SLOPE INSTABILITY: I BEACHING li FLOWS m SLIDING (UNFROZEN) ]l[ SLIDING (PERMAFROST) III DENOTES AREA EXTENT AND TYPE OF INSTABILITY I (]l[) PRIMARY BEACHING INSTABILITY WITH SOME POTENTIAL SLIDING I -li BEACHING AND FLOWS POSSIBLE IN DEFINED AREA NORMAL MAXIMUM OPERATING LEVEL -----NORMAL MINIMUM OPERATING LEVEL A A RIVER MILES t J SECTION LOCATION I. REFER TO FIGURES 5.1 AND 5.2 FOR DETAILED DESCRIPTION OF TYPE OF SLOPE INSTABILITY MODELS 2. NO DELINEATION OF PERMAFROST AREA ABOVE ELEVATION 2300 FEET 3. AREAS OF POTENTIAL PERMAFROST BASED PRINCIPALLY ON AIR PHOTO INTERPRETATION AND WILL REQUIRE FUTURE VERIFICAT ION SCALE O~~~~IO~OOiiiiiiiiiiiiii2~000 FEET FIGURE 5.17 i. -t- R-II N-Il WATANA SLOPE STABILITY II r r 'j; t SLOPE INSTABILITY AREAS OF CURRENT SLOPE INSTABILITY: TYPES OF BEACHING I FLOWS lJ: SLIDING (UNFROZEN) :m: SLIDING I PERMAFROE~~) AND TYPE OF INSTABILITY ~/ DENOTES AREA EXTINSTABILITY WITH SOME PRIMARY BEACHING I (lll:) POTENTIAL SLIDING SSIBLE IN DEFINED AREA I-ll: BEACHING AND FLOW~P:ATING LEVEL ----NORMAL MAXIMUU: OPERATING LEVEL -----NORMAL MINIM RIVER MILES SECTION LOCATION AREA OF POTENTIAL PERMAFROST NOTES --51 AND 5.2 1. REFER TO FIGO~R~~PE. OF SLOPE DESCRIPTION 2. NO DELINEATION OF PERMAFROST FOR DETAILED INSTABILITY MODELS AREA ABOVE ELEVATION 2300 FEET ST BASED PRINCIPALLY 3. ARE OTO INTERPRETATI AS OF POTENTIAL PERMAOFN~ND WILL REQUIRE ~~T~~:~ERIFICATION . SCALE FIGURE 5.IS r -,2500LACUSTRINE20001500RESERVOIRLEVEL(HIGH)RESERVOIRLEVEL(LOW)PLAINTERRACEASSUMPTIONS:BASALTILLtPRIMARILYFROZENNOTE:SEEFIGURE5.11fORSECTIONLOCATIONo5001000FEETSCALE~j~~~~~;;;;;;;;;;;;;;lSECTIONF-FWATANARESERVOIRPOTENTIALROTATIONALSLIDESANDFLOWSFIGURE5.19 2500....l-I--I-wWlJ..I-zQ2000I-~>W..Jw1500....'"RESERVOIRLEVELIHIGHI.•.•.S7i'?!fA?i1:~@~t!5z%J}i~~g~E~~~~SRESERVOIRLEVEL(LOW)..,"~":"'".•; ;!.:...•.:.,;:;,.•....~;.''!•.•..~.i...;'-~~-~~~."~._.ASSUMPTIONS.SANOYMATERIAL,FROZENNOTE:SEEFIGUREt5.lGFORSECTIONLOCATIONo5001000FEETSCALE~r~~~~~~.ISECTIONG-GWATANARESERVOIRAREA.OFFLOWFAILURESFIGURE5.20 2500I-WWlL.52000~W-1W1500RESERVOIRLEVEL(HIGHI4@:;::;~~:J:~~~~~_~.~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~.~.~...~.~.~.•~.•&'.'~."·.'o.~~~..,.,.d.ai;'.':-~O"'oP""O••••••:o.•..(J·.·.~#.•.··.uRESERVOIRLEVEL(LOW~)~.-r:"...•~':'.,;:~o:..:;;:..:...~.::~..•.:.:...~::.:.....::.~~-~I·'t~..~,'t~...·~···"tI·.·,..·.o~~lal,"'r~··:...e.•.'"rWATANACREEKJ.TILLlem',,---_BEDROCK'JASSUMPTIONS:STRATIGRAPHYCONSISTSOFGLACIO-LACUSTRINESANDSANDSILTS,TILL.TILLISFROZEN,LACUSTRINEMAYBEPARTLYFROZEN.NOTE:SEEFIGURE5.7FORSECTIONLOCATIONo5001000FEET.~~~~----_..!SCALECISECTIONE-EWATANARESERVOIRAREAOFPOTENTIALFLOWSFIGURE5.21 ___~~7t"c.'7:""rP,~'q·'0'~',o",o~o.,.'7'o,.'~s;::';':/':;"["1""~.., .~.,-:"<1-O'IIf.ih,·~,.....,.,.,.;Ii:.,.0."\TILL..-..0 ,"!BEDROCK)15002500i='~RESERVOIRLEVEL(HIGH)u.zRESERVOIRLEVEL(LOW)0i=2000~W..JWASSUMPTIONS:BASALTILL.THINVENEEROFLACUSTRINEMAtERiALFROZENINPLACES.NOTE:SEEFIGURE5.6FORSECTIONLOCATIONo5001000FEETSCALEi~~~~~~iiiiiiiiiiiiiiiiiiiiiiii~1SECTION0-0WATANARESERVOIRPOTENTIALBEACHINGFIGURE5.22. WATANA IWol FIGURE 5.31 \ --~ / ( .> _r ·---... ........ ~0 i-.. l ...... ' I DEVIL CANYON RESERVOIR INDEX MAP I \ \ ) \ LOCATION MAP / )·-... I I SCALE : ~0 ~~4iiiiliiiiiiiiiiiiiil MILES ----·-NORMAL MAXI- OPERATING LEVEL EL . 14!56 --2ooo ~CONTOUR IN FEET ABOVE MSL SCALE :O ~~~!i;;;;;;;;iiiiiiiiiiiiiii2 MILES FIGURE 5.23 ? I I ( ( ' ' ) / -~ \ / ( "'-..___ . ..- /;, '· } r ; O.t• "'' l'tt.Gto,•o."r 1'· 19 !' ~<;Odf "'> •000 COO" IN' ""II•'"• i()IJ" St1[(1 !JiOEl ' ,, ' DEVIL CANYON SLOPE STABILITY MAP D AREAS OF CURRENT SLOPE INSTABILITY TYPES OF SLOPE INSTABILITY: I BEACHING l[ FLOWS m SLIDING (UNFROZEN) .Ill SLIDING (PERMAFROST) III DENOTES AREA EXTENT AND TYPE OF INSTABILITY I (.Ill) PRIMARY BEACHING INSTABILITY WITH SOME POTENTIAL SLIDING I-n BEACHING AND FLOWS POSSIBLE IN DEFINED AREA NORMAL MAXIMUM OPERATING LEVEL RIVER MILES A A t 1 SECTION LOCATION D AREA OF POTENTIAL PERMAFROST I. REFER TO FIGURES 5.1 AND 5.2 FOR DETAILED DESCRIPTION OF TYPE OF SLOPE INSTABILITY MODELS 2 NO DELINEATION OF PERMAFROST AREA ABOVE ELEVATION 150Q FEET 3. AREAS OF POTENTIAL PERMAFROST BASED PRINCIPALLY ON AIR PHOTO INTERPRETATION AND WILL REQUIRE FUTURE VERIFICATION . SCALE 0~~~10~0~0~-2~000 FEET FIGURE 5 .24 'T L " DEVIL CANYON SLOPE STABILITY MAP I D AREAS OF CURRENT SLOPE INSTABILITY TYPES OF SLOPE INSTABILITY: I BEACHING ll FLOWS m lll SLIDING I UNFROZEN) SLIDING I PERMAFROST) II I DENOTES AREA EXTENT AND TYPE OF INSTABILITY I (Ill:) PRIMARY BEACHING INSTABILITY WITH SOME POTENTIAL SLIDING I-n BEACHING AND FLOWS POSSIBLE IN DEFINED AREA NORMAL MAXIMUM OPERATING LEVEL RIVER MILES A A t i SECTION LOCATION D AREA OF POTENTIAL PERMAFROST I. REFER TO FIGURES 5 .1 AND 5 .2 FOR DETAILED DESCRIPTION OF TYPE OF SLOPE INSTABILITY MODELS 2 NO DELINEATION OF PERMAFROST AREA ABOVE ELEVATION 1500 FEET ~ AREAS OF POTENTIAL PERMAFROST BASED PRINCIPALLY ON AIR PHOTO INTERPRETATION AND WILL REQUIRE FUTURE VERIFICATION 0 1000 2000 FEET SCALE ~~~ FIGURE 5.25 I lr4 !,120,000 111 l,Zl~.ooo 0.1• II PN•I.,O ... f 7·19·8• 5tl1.-,~, oooo· Cll'tour le,.,.,.,. 100 I DEVIL CANYON SLOPE STABILITY MAP / I D AREAS OF CURRENT SLOPE INSTABILITY TYPES OF SLOPE INSTABILITY: I BEACHING li FLOWS m SLIDING (UNFROZEN) .Ill SLIDING (PERMAFROST) III DENOTES AREA EXTENT AND TYPE OF INSTABILITY I (Ill:) PRIMARY BEACHING INSTABILITY WITH SOME POTENTIAL SLIDING I -n BEACHING AND FLOWS POSSIBLE IN DEFINED AREA NORMAL MAXIMUM OPERATING LEVEL • RIVER MILES A A t ! SECTION LOCATION D AREA OF POTENTIAL PERMAFROST 1 REFER TO FIGURES 5.1 AND 5.2 FOR DETAILED . DESCRIPTION OF TYPE OF SLOPE INSTABILITY MODELS 2 NO DELINEATION OF PERMAFROST AREA ABOVE ELEVATION 1500 FEET 3. AREAS OF POTENTIAL PERMAFROST BASED PRINCIPALLY ON AIR PHOTO INTERPRETATION AND WILL REQUIRE FUTURE VERIFICATION 0 1000 2000 FEET SCALE FIGURE 5 .26 "'),1 '1~,000 .. l,200,000 ----------..--.... ;::. •u ' I"....:, /~ '---------..--~~::-~~-... ·~.: ~ e • TI I I DEVIL CANYON MAP SLOPE STABILITY --r- LEGEND INSTABILITY D AREAS OF CURRENT SLOPE TYPES OF BEACHING SLOPE INSTABILITY: I l[ m Jl[ FLOWS NFROZEN) SLIDING ( ~ERMAFROST) E OF INSTABILITY ~~~~~~S( AREA ~~T~~A~~~T~YPWITH SOME ~~~) ~~~E~RTiA~E~~~~ING WS POSSIBLE IN DEFINED AREA BEACHING AND FLO OPERATING LEVEL NORMAL MAXIMUM r-n RIVER MILES SECTION LOCATION PERMAFROST AREA OF POTENTIAL NOTES . ·--R DETAILED 5 ES 5 I AND 5 .2 F?NSTABILITY MODEL I. REFER rgO~IG~~ TYPE OF SLOPE ABOVE ELEVATION DESCRIP AFROST AREA N OF PERM 2 NO DE~I~~TIO ASED PRINCIPALLY 3. ~:~5 OF POT~N.i~~~~~~~~~D SWILL REQUIRE ON AIR p~~~~FICATION FUTURE SCALE FIGURE 5.2 7 ' \ ) Oo ).11COOC: o. •• r ~,,-. '-. ·' DEVIL CANYON SLOPE STABILITY MAP D AREAS OF CURRENT SLOPE INSTABILITY TYPES OF SLOPE INSTABILITY: I BEACHING li FLOWS m SLIDING (UNFROZEN I llZ SLIDING (PERMAFROST I III DENOTES AREA EXTENT AND TYPE OF INSTABILITY I (Ill:) PRIMARY BEACHING INSTABILITY WITH SOME POTENTIAL SLIDING I-n BEACHING AND FLOWS POSSIBLE IN DEFINED AREA NORMAL MAXIMUM OPERATING LEVEL 1 RIVER MILES A A t .t SECTION LOCATION AREA OF POTENTIAL PERMAFROST I. REFER TO FIGURES 5 .1 AND 5 .2 .FOR DETAILED DESCRIPTION OF TYPE OF SLOPE INSTABILITY MODELS 2 NO DELINEATION OF PERMAFROST AREA ABOVE ELEVATION 15 0 0 FEET 3 AREAS Of POTENTIAL PERMAFROST BASED PRINCIPALLY ON AIR PHOTO INTERPRETATION AN[) WILL REQUIRE FUTURE VERIFICATION SCALE 0~~~10~00;;;;;;;,;;;;;;;20~00. FEET FIGURE 5. 28 8 1- _ _(_ lill,"'.,O(O !- Q I ~r~~J.~.ooo II; ~.20:1.,000 "'),2!0,000 0..1• ¢1P~!Of'IIIIIIJ J.ft It t~o<t t •OO<l C<:~':eu• lntt••<ll rCN- ~ 8 ,.; ?. '""i l (/ I _./ ! ) / -•· I , I '\ C ( Fl URE 5.34) I I ·I ~ " t D AREAS OF CURR ENT SLOP E INSTABILITY TYPES OF SLOPE INSTABILITY: I BEACHING li FLOWS m SLIDING (UNFROZEN I .Ill SLIDING (PERMAFROST) /I / DENOTES AREA EXTENT AND TYPE OF INSTABILITY I (IlL) PRIMARY BEACHING INSTABILITY WITH SOME POTENTIAL SLIDING I -JI BEACHING AND FLOWS POSSIBLE IN DEFINED AREA NORMAL MAXIMUM OPERATING LEVEL ' RIVER MILES A A t i SECTION LOCATION D AREA OF POTENTIAL PERMAFROST L REFER TO FIGURES 5,1 AND 5 .2 FOR DETAILED DESCRIPTION OF TYPE OF SLOPE INSTABILITY MODELS 2 . NO DELINEATION OF PERMAFROST AREA ABOVE ELEVATION 1500 FEET l AREAS OF POTENTIAL PERMAFROST BASED PRINCIPALLY ON AIR PHOTO INTERPRETATION AND WILL REQUIRE FUTURE VERIFICATION SCALE o~~~~~ooliio~iiiiiiz~ooo FEET FIGURE 5.29 • >,2>0,000 Q I CM:••ofP'at•e,.._.., 1 '" 111 5ca•• 1" 1000' '-~-lf'O••••O• r()ff / .. + DEVIL CANYON SLOPE STABILITY MAP D AREAS OF CURRENT SLOPE INSTABILITY TYPES OF SLOPE INSTABILITY: I BEACHING 1r FLOWS lir SLIDING I UNFROZEN I Ill SLIDING (PERMAFROST) /I I DENOTES AREA EXTENT AND TYPE OF INSTABILITY I (Ill:) PRIMARY BEACHING INSTABILITY WITH SOME POTENTIAL SLIDING I-n BEACHING AND FLOWS POSSIBLE IN DEFINED AREA NORMAL MAXIMUM OPERATING LEVEL RIVER MILES A A t f SECTION LOCATION I REFER TO FIGURES 5.1 AND 5 .2 FOR DETAILED DESCRIPTION OF TYPE OF SLOPE INSTABILITY MODELS 2 NO DELINEATION OF PERMAFROST AREA ABOVE ELEVATION 1500 FEET 3. AREAS OF POTENTIAL PERMAFROST BASED PRINCIPALLY ON AIR PHOTO INTERPRETATION AND WILL REQUIRE FUTURE VERIFICATION SCALE O~IIIIIIIIII~IO~OOiiii;;;;oiiii2~000 FEET FIGURE 5.30 g § -~f-" e . ' "" ~.uo.ooo L I ~ 111 ~uo.ooo • J,::r3~.ooo 0C • I '---~ ..~.-·JI_·__J § ~ _j_ DEVIL CANYON SLOPE STABILITY MAP § t .)__ J. ---. ./ ~ -: , +- "'' \_ oO~ -··'"' '~ _......-- J ' !\/"\ ~ AREAS OF CURRENT SLOPE INSTABILITY TYPES OF SLOPE INSTABILITY: I BEACHING li FLOWS m SLIDING (UNFROZEN l Il7: SLIDING (PERMAFROST l III DENOTES AREA EXTENT AND TYPE OF INSTABILITY I (Ilr) PRIMARY BEACHING INSTABILITY WITH SOME POTENTIAL SLIDING I -li BEACHING AND FLOWS POSSIBLE IN DEFINED AREA NORMAL MAXIMUM OPERATING LEVEL -----NORMAL MINIMUM OPERATING LEVEL X RIVER MILES A A t ! SECTION LOCATION I. REFER TO FIGURES 5 .1 AND 5.2 FOR DETAILED DESCRIPTION OF TYPE OF SLOPE INSTABILITY MODELS 2 . NO DELINEATION OF PERMAFROST AREA ABOVE ELEVATION 1500 FEET 3. AREAS OF POTENTIAL PERMAFROST BASED PRINCIPALLY ON AIR PHOTO INTERPRETATION AND WILIL REQUIRE FUTURE VERIFICATION SCALE O~"""""~I~OOiiiOi;;;;;;iiilii2iiOOO FEET FIGURE 5.31 ..uIr,-.T2000~&oJ&oJILZQ1500...~&oJ..JuJ1000I,fJf,J ',~.RESERVOIRLEVEL••~••~~.-:-7£''''---~~~••~.COLLUVIUM8BEDROCK,-~RIVERASSUMPTIONS:COLLUVIUM,UNFROZENBEDROCKPROBABLYINCONTACTWITHTHERESERVOIRLEVEL--ri'.111-----.I1NOT£:SEEFIGURE5.26FORSECTIO~LOCATIONo5001000FEETSCALEi!SECTiONB-BDEVILCANYONRESERVOIRPOTENTIALMINORBEACHINGFIGURE5.32• 'U-.Irr1-;-.'1~~I2000r-J--l'~I-~-.,,.~-f',.'-i.'-'T~--T-ri-Ti,ltl-Ii~1500wwILzo...~~1000wRESERVOIRLEVEL.~-~~\~/~"~.,.7<.."'--\.BEOROCH,.'-<RIVERASSUMPTION:THINUNFROZENVENEEROF'SANDYTILLTILLNOTE:SEEFIGURE8.25FORSECTIONLOCATIONoSCALE"i5001000FEETSECTIONA-ADEVILCANYONRESERVOIRPOTENTIALMINORBEACHINGFIGURE5.33[iii] '~IIIr-=_rJ-I-0=...,,!'I~-="lI '"J~1·='--~lIi',Iai---,POSSIBLETOEEROSION,~.~.,.(j..~..,....~~-,~...__•__~~.,.,~.'.'~'.<".,~"'.'.:.:.,.::;">:.':',:;'c';;;:i,;;-:;~*:'...'lc.',·,.~'~.".,~/;'~'"..:.,;,.o,:,,'!~::•.',;.~.~.~::~.:.'':~'.k:~'o.i.'O·.~~··.....".-.•......,,''..,,-'". .'.••_._-.'~'l'~'~'".'••.••"'.'"''.t'i:';.;,..:.~.o·~·o..:·..• •.•.•••POTENTIALFAILURESURFACE25002000J-ILl~1500tIC'\JC'I-RESERVnlDZ0~~~..->•.-.....R'VERILl...JILl1000ASSUMPTIONS:BASALTILL.FROZEN500NOTE:SEEFIGURE5.29FORSECTIONLOCATIONO.5001000FEETSCALEiISECTIONC-CDEVILCANYONRESERVOIRPOTENTIALLARGESLIDEFIGURE5.34[ii] 6 -RECOMMENDATIONS It is recommended that typical slope conditions outlined in this report be fur ther investigated du ring subsequent phases of the project in order to deter mine: (a) If potential instability actually exists and the magnitude of this poten tial for instability at a given location; and (b) If beaching or sl iding will exist at major crossing sites for migrating herds. This investigation should include dr illing, instrumentation and laboratory analysis to confirm the findings in this study . Since only one significant existing landslide has been identified in this study, it is also recommended that further study be directed to this slide with due consideration to excavat ing a clear channel to the north west of the existing river channel at this loca tion to preclude blockage of the channel by future sliding. It is anticipated that this excavation could be done during the construction of the Watana Dam when granular material is being excavated from the river channel downstream at the dam. Under no circumstances should material be borrowed in the river stretch below this slide mass. 6-1 BIBLIOGRAPHY Brown, W.G., and Johnston, G. H., 11Dikes on Permafrost: Predicting Thaw and Settlement", Canadian Geotechnical Journal, vol. 7, pp. 365-371, 1978. Csejtey, B. Jr., Foster, H.L., and Nokleberg, W.J., "Cretaceous Accretion of The Talkeetna Superterrane and Subsequent Development of The Denali Fault in Southcentral and Eastern Alaska", Geological Society of America, Abstract with Programs, pp. 409, 1980. Csej tey, B. Jr., Nelson, W.H., Jones, O.L., Silberling, N.J., Dean, R.M., Morris, M.S., Zamphere, M.A., Smith J.G., and Silberman, M.L., "Reconnais sance Geologic Map and Geoc hronology, 1alkeetna Mountain Quadrangle, Northern Part of Anchorage Quadrangle, and Southwest Corner of Healy Quadrangle, Alaska; U.S. Geological Survey, Open File Report 78-5�8A, pp. 60, 1978. Hoek, E., and Bray, J.W., Rock Slope Engineering, Lo ndon, In stitution of Mining and Metallurgy, pp. 150-15 3, 1977. McRoberts, E.C., and Morganstern, N.R., "The Stability of Thawing Slopes", Canadia n Geotechnical Journal, val. 11, no. 4, pp. 447-469, 197 4. McRoberts, E.C., and Morganstern, N.R., "Stability of Slopes in Frozen Soil, Mackenzie Valley, N.W.T.", Canadian Geotec hnical Journal, val. 11, pp. 55 4-573, 1974. Newbury, R.W., Beaty, K.G., and McCullough, G.K., "Initial Shoreline Erosion in a Permafrost Affected Reservoir, Southern India n Lake, Canada", in North American Contribution to The Third International Conference on Permafrost, Edmonto n, Alberta, National Academy of Sciences, Was hington, pp. 833-839, 1978. Smith, T.E., "Re gional Geology of The Susitna-MacLaren River Area", Alaska Division of Geological and Geophysical Survey. Annual Report, pp. 3-6, 1974. Turner, D.L., and Smith, T.E., "Geochronology and Generalized Geology of The Central Alaska Range, Clearwater Mountains, and Northern Talkeetna Moun tains", Alaska Division of Geological and Geophysical Survey, Open File Report 72, pp. 11, 197 4. U.S. Army Corps of Engineer s, "Upper Susitna River Basin, Alaska, Hyd roelectric Power Supplemental Feasibility Report, 1979. Varnes, D.J., "Landslide Types and Processes", in E.B. Eckert (ed.), Landslid es and Engineering Practice, Highway Reserve Board Special Report No. 29, pp. 20-45, 1958.