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INTRODUCTION AND DAM DESCRIPTION   RF A.` ` Purpose(#` XX` ` The purpose of this report is to develop conceptual design alternatives for the Dulce Lake Dam Safety project and to determine the most feasible  R alternative for final design. *(#`  Rt B.` ` Dulce Lake Dam Description(#` XX` ` Dulce Lake Dam is located on the Jicarilla Apache Indian Reservation in northcentral New Mexico about four miles south of the town of Dulce. The dam is owned and operated by the Jicarilla Apache Tribe. The Tribe utilizes the lake for recreation and irrigation.(#` XX` ` The dam was originally constructed in 1903 and was raised in 1910 to a total height of about 20 feet and 400 feet in length. Prior to its raising in 1910, it had been overtopped. In 1936, it was raised an additional 7 feet to increase freeboard. In 1952, the spillway was moved from the right abutment to its current location at the left abutment.(#` XX` ` Dulce Lake Dam is an earthen embankment with a crest length of approximately 710 feet and a nominal crest elevation of 7050.5 National Geodetic Vertical Datum (NGVD). The embankment is unzoned with the lower portions generally impervious and the upper 7 feet a variety of material ranging from sand to clay. The depth of foundation alluvium under the dam ranges from 0 feet to over 100 feet. The foundation contains extensive zones of potentially liquefiable loose fine and silty sand. There is no cutoff in the foundation.(#` XX` ` Based on the depth to the bottom of the outlet valve access shaft, the damr(,)) has an estimated structural height of 27 feet. The hydraulic height, spillway crest to toe of embankment, is approximately 14.5 feet. The designed freeboard above spillway floor is about 6 to 7 feet, but functionally, due to sandbags and fish screens in the spillway, the actual freeboard is about 4 to 5 feet. As the floor of the spillway is continually regraded to accommodate traffic rutting, the spillway floor elevation is not constant, however, it is approximately 7044 NGVD.(#` XX` ` The dam abuts a high sandstone bluff on the left abutment and a sandstone ridge on the right abutment. The right end of the dam widens and doglegs to the southeast to form a parking area and a road junction with Highway 64 which forms part of the right abutment.(#` XX` ` An uncontrolled service spillway is cut into sandstone on the left abutment. The spillway floor is primarily sandstone but the right spillway bank which is the left end of the dam is primarily erodible fill. With the lake level at the top of the dam crest and no fish screen in place, the spillway has a maximum capacity of 1,500 cfs. The high sandstone bluff on the left abutment and location of Highway 64 on the right abutment effectively preclude increasing the spillway capacity.(#` XX` ` The outlet works consists of a 30 inch diameter corrugated metal pipe (CMP) inlet, and a 15 inch diameter cast iron outlet pipe under the upstream embankment into a 4 foot diameter valve access well. The outlet flow is controlled by a partiallyoperable gate valve. The flow is discharged from the well through a 12 inch CMP that extends approximately 500 feet downstream. A 4 inch diameter perforated CMP toe drain system ties into the outlet pipe approximately 20 feet downstream of the toe of the dam. (#` XX` ` (#` XX` ` The dam impounds approximately 1,178 acrefeet of water at the top of the spillway at the time of the most recent survey. (Note: this value was(,)) incorrectly reported in the Deficiency Verification Analysis (DVA). A spillway elevation of 7037.7 was shown in the DVA with storage of 480 acrefeet. Elevation 7038 had been referenced from earlier SEED reports and included in an earlier BHPG document this was not corrected in the DVA to reflect surveys and storage calculations used in the DVA).(#`  R. XC.X` ` Dulce Lake Dam Deficiencies(#` XX` ` A description of identified deficiencies for Dulce Lake Dam is presented in this section. The deficiencies are based on the DVA report. The listings are generally in order of priority.(#` XX` ` Dulce Lake Dam is a high hazard structure located very close to downstream inhabited residences. BHPG recommended installation of an early warning system for high water or dam break as an essential priority. The system has been designed and installed.(#` XX` ` The remaining deficiencies are as follows:(#`  R X` ` 1) The dam has inadequate spillway capacity. Addition of spillway capacity is restricted by the high sandstone bluff at the left abutment and the location of Highway 64 at the right abutment. The current spillway impedes access to recreation areas on the west side of the lake and capacity is usually restricted by trash on the fish screen and placement of sandbags to raise the lake level.(#  R ` ` 2) The alluvial foundation which extends to depths of more than 100 feet contains zones of materials which are potentially liquefiable under the design earthquake. Densification or stabilization is complicated by the depth of alluvium under the existing embankment. Alternative dam sites downstream or upstream would probably have a similar alluvial foundation, however, no investigations have been made. (# (,))Ԍ R ` ` 3) The outlet works is only partially operable. In addition to reservoir control, the outlet is required for irrigation releases.(#  R ` ` 4) The existing spillway is subject to scour and the right side of the spillway can erode into the embankment.(#  Rt ` ` 5) The foundation and abutments have uncontrolled seepage. The exit gradients of this seepage are not considered significant enough to be an imminent piping hazard. The volume of seepage is not particularly detrimental to lake levels since there is perennial inflow from the upstream drainage.(#  RE ` ` 6) The dam needs an allweather roadway. The crest roadway has adequate width but becomes almost impassible in wet weather and spillway flow often precludes passage.(#  R\ ` ` 7) The embankment slopes have, in localized areas, factors of safety which are below acceptable values.(# XX` ` It is noted that the restrictions on developing additional spillway capacity and the need to densify or stabilize the foundation to improve dynamic stability result in the practical need to remove and replace the existing embankment.(#`