C153445 Feasibility Study - Laserfiche WebLink

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4. Install filter drain and berm on the middle section of the south dike. Geologic Investigations The general geology of the area consists of Dakota sandstone. Hard to friable feldspar, quartz, .and sandstone occu~ in the north abutment. The formation dips f~om 0 - 400 south-southeast. Grey marly limestone (Mancos shale). lies flat to 70 dip southward as seen at the spillway. The Mancos shale, which is about 700 feet thick, overlies Dakota sandstone (about 200 f feet thick) dipping southward at about 120 i feet per m~le. .The geo.logic investigations conducted to support this study were minimal. Soil samples and in-place densities were taken at one location on the west dike and one on the south dike. Sieve analysis were performed on the samples to determine a gradation curve. The soils at the sample sites are classified as clay. The sample site on the west dike was just south of the horseshoe bend on a sectio~ of the embankment about 25 feet high (see Drawing V-B). Two soil samples were taken, one from the embankment and one from the foundation. . The sample site for the south dike was about the middle of the middle section, over one of the seepage locations (see Drawing V-B). Again samples were taken from the foundation and the embankment. Results from the tests are described on Table V-A. Designs and Structures 1. Grourid Recontouring - when Summit Reservoir was enlarged in 1938, material was borrowed from just below the toe of the embankment. These areas were never recontoured so water that seeps through the embankment collects in the borrow areas. The water that collects in the borrow areas form marshes, ponds, and promote vegetative growth that seriously inhibits inspection of the embankment. Also the collected water, if on the toe of the dike, may saturate the embankment sufficiently to cause slumping. About 2100 feet of the west dike and 1400 feet of the south dike needs to be recontoured. (See Drawing V-C for locations). . Recontouring the west dike generally involves reshaping the ground to its natural gradient which slopes away from the dike. Cuts would be made during the recontouring with excess material placed away from wat~r drainage paths. One area, about two thirds of the way south on the west dike will be a little more difficult because the ground is fairly flat. This section appears to have quite a lot of seepage. The ground will be recontoured to collect water at one surface drain which will include a measuring flume. Use of the measuring flume will -21-