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I I I I I I A.6. GEOTECHNICAL EVALUATION I. Stability. The dam stabilIty was not numerIcally analyzed at this time due to the use of exIsting geotechnical data that will have to be checked at a later date. Based on past analyses and design of dams using similar soils, we are confident no stability problems would be expected with 3H to I V slopes. The existing geotechnical Investigation does not Indicate any foundation or embank- ment deficiencies or problems that would be expected to create stability problems. The stability of the dam and foundation will be rigorously analyzed after a new geotechnical investigation is conducted and strength tests conducted on the expected fill materials. I I I I I I I I I I I I I 2. Seepage. A rigorous seepage analysis was not conducted on the dam at this time. The seepage was roughly estimated for the quantity of flow expected through the sand layer found In the central portion of the dam. The seepage through the dam fIlI and clay foundation are expected to be low as the clays in both are expected to have permeabllltles in the range of 10-6 to 10-6 ce~tImeter_~ per second. The sand layer was estimated to have a permeability of 10 to 10 centimeters per second. The seepage due to the sand layer was estimated to be 1.0 cubic feet per second or 2 acre-foot per day for the 1200 foot of estimated lateral width. This Is expected to be greater than will be experienced and will be analyzed more rigorously prIor to the final design. A.7. HYDROLOGIC AND HYDRAULIC EVALUATION The hydraulic and hydrologic design references and hydrologic report are included In Appendix C. This Includes the Inflow and outflow hydrographs for a 75% and a 100% PMP flood and the stage-discharge curves for a 300 foot and 350 foot spillway. The capacity charts for the various sizes of outlet conduits considered are also Included In Appendix C of this report and are discussed in the next section. A.B. STRUCTURE PLANS I. Embankment. The existing main dam and saddle dam embankments require regrading and additional fill to bring them to proper freeboard height and to a consistent slope. The main dam and saddle dam crests will be raised approx- Imately 3 to 5 feet In elevation. The main dam will require fill on the upstream slope to provide for the additional crest height. The upstream fill will be sandy clay materials and will also provide some protection against seepage trough the dam embankment. Adequate sandy ciay borrow exists on the site In the reservoir bottom to provide for all the fills required. The potential borrow sources contain several times the quantity of material required for the project. The embankment sections considered are at slopes of 3 horizontal to I vertical. These slopes are considered to be the minimum face slopes recommended from the practical considerations for placement of rlprap and bedding and for seeding the downstream section. Steeper slopes could be permitted based on the structural stability but would result In thicker rlprap sections, problems with the down- stream slope erosion control, and Increased unit cost for application of the erosion protection. Flatter slopes are not deemed necessary from either PAG! I Cbapter V - No. 6 Felliblllty