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As shown in Figure 5, the phreatic surface is slightly different at two selected cross section B -B' and C -C'. The difference could be attribut- able to differences in the characteristics of the core material at this location or to differences in the permeability of the foundation material. Section C -C' has a thicker alluvial soil layer and weathered bedrock zone than Section B -B'. Section C -C' would therefore exhibit a greater probability of higher permeability zones occurring either naturally or as a result of settlement within the alluvial soil and/or weathered bedrock. The general characteristics of the flow, i.e., rapid drop of the flow net into the foundation are, however, similar and consistent with the assumed condition in the dam and foundation. 3-6 stream toe or on the natural ground surface downstream from the dam. o Flow through the alluvial layer (and/or pond bottom) into the weathered rock, beneath the dam and exiting either through the alluvial soils or into the collection systems downstream of the dam. In the first flow system, seepage can move easily through the pervious fill of the upstream dam shell. Within the dam core, the phreatic surface drops rapidly, as shown on Figure 5, because of (a) high head in the less pervious core material; (b) the potential for vertical peme- ability equal to or greater than horizontal permeability; and (c) the permeable foundation materials beneath the downstream slope of the dam. The rapid drop is exemplified by piezometers P -21A, P -21B, and P- 26. The differential pressures at the same vertical line (P -21A and P - 21B) indicate a steeply dropping flow net. The low phreatic surface beneath the downstream edge of the dam crest further supports the rapidly dropping flow net. Since little or no water apparently exists in the chimney or blanket drain, the seepage moving through the core finds an easier path downward into the foundation than horizontally into the chimney drain. As shown in Figure 5, the phreatic surface is slightly different at two selected cross section B -B' and C -C'. The difference could be attribut- able to differences in the characteristics of the core material at this location or to differences in the permeability of the foundation material. Section C -C' has a thicker alluvial soil layer and weathered bedrock zone than Section B -B'. Section C -C' would therefore exhibit a greater probability of higher permeability zones occurring either naturally or as a result of settlement within the alluvial soil and/or weathered bedrock. The general characteristics of the flow, i.e., rapid drop of the flow net into the foundation are, however, similar and consistent with the assumed condition in the dam and foundation.