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Show Preliminary Draft - Subject to Revision Supplement to Salinity, Chemistry, and Water Issues by J. Wallace Gwynn Utah Geological Survey September 23, 1999 INTRODUCTION During the SRC's review of the GSL CMP- PD, questions were raised concerning the adequacy of the information contained in the sections on salinity, chemistry and other water issues. This draft appendix provide additional information on these topics. ISSUES Effect of the Breach A 300- foot opening was breached in the western Rambo Fill portion of the SPRR causeway near Lakeside; it was opened on August 1, 1984. The purpose of the breach was to help reduce flooding on the south arm of the lake by reducing the head differential of nearly four feet that had developed between the south arm ( higher elevation) and the north arm ( lower elevation). The obvious effect of the breach was that within about two months, the head differential was reduced to less than a foot. In addition to reducing the head differential, the breach allowed a major redistribution of the salinity and salt loads between the south and north arms. Large volumes of south- arm brine ( lower salinity) flowed into the north arm as the head differential was reduced. South- to- north flow continued through the breach opening until the level of the south arm reached the breach- bottom elevation of 4195- 4200 in about 1994. These large volumes of lower- salinity water helped to reduce the salinity of the higher- density north- arm brines ( Gwynn and Sturm, 1987). During the same period of time, higher- salinity north- arm brine moved through the depths of the breach opening, as return flow into the bottom of the south arm. This movement of north- arm brine, which ceased about December 1988, ( 1) further reduced the overall salinity ( and salt load) of the north arm, and ( 2) increased the overall salinity ( and salt load) of the south arm. From 1988 until 1999, only south- to- north flow occurred through the breach opening ( though there was little or no flow in either direction during the 1994 to 1997 period). North- to- south return flow resumed in 1999 ( USGS breach- flow measurement records) 373 |