Description of the Environmental Setting
The Lodi area is basically flat with elevations ranging from 30 to 50 feet above sea level. The park site is located in the floodplain of the Mokelumne River with elevations ranging from 35 to 45 feet, with the exception of the lake itself, where there is approximately a 20-35 foot elevation range. The surface area of Lodi Lake is 36 acres and the average depth is about seven feet, except in the swimming area where the banks slope steeply from the normal surface to about elevation 35 feet. Slopes, excluding the lake, are gentle (less than 3%) and are toward the south to a levee which separates the site from adjacent residential uses.
The Mokelumne River begins in the eastern slopes of the Sierra Nevada Mountains and flows westerly to the San Joaquin River. Its major surface flow occurs from December to May. The river is regulated about one-half mile downstream of Lodi Lake Park by the Woodbridge Dam, owned by the Woodbridge Irrigation District. Woodbridge Reservoir is controlled by a spillway at the dam that utlizes flashboards for a part of the year.
The operation of the spillway and reservoir are regulated by the California Division of Safety of Dams, Department of Water Resources. The operating plan permits use of flashboards to raise reservoir stage during the period Februrary 15 through October 31 each year. The approved flashboard crest elevation is 41 feet. Customarily the district does not install floorboards until after March 1. The operating regimen of Woodbridge Reservoir is such that when flashboards are in place during the majority of the year (including the summer), water is stored against the flashboards to elevation 41 feet and backed into the Lodi Lake area. When flashboards are removed, Woodbridge Reservoir drains to the permanent crest elevation. As a result, the water stored in Lodi Lake drains.
Prior to construction of Camanche Reservoir, the 58-acre park addition was subject to periodic flooding. The last major flood occurred in 1955 when the flow line reached the level of the levee. The amount and extent of damage caused by any flood depends on the topography of the area flooded, depth and duration, velocity of flow and developments in the floodplain. Because of the Camanche Reservoir and other related projects, the Army Corps of Engineers stated in their flood hazard report of August, 1970, and revised report in April, 1971, that an intermediate regional flood like that of 1955 could now be predicted to occur once per 100 years. During a 100-year level flood event, Lodi Lake can be expected to rise about two feet above its normal summer lake level of 41 feet.
In a study, completed by the Spink Corporation in 1974, to assess and evaluate the feasibility and methods of providing for year-round storage of waters in Lodi Lake, it was pointed out that recreational and aesethetic uses of the lake are water quality dependent, and that certain water quality standards must be met to preserve or enhance these uses of Lodi Lake. Extensive tests were undertaken to determine the water quality of present sources of water for Lodi Lake Park. The data indicated that surface waters and ground water were in compliance with accepted standards which should be met to preserve present recreational uses of Lodi Lake. The storm drain waters were generally not in compliance.
The park site is part of the floodplain of the Mokelumne River Floodplain Basin. The soils consist of Columbia, very fine, sandy loam. The soil has been formed from recent alluvium from a wide variety of parent rock material. The soil is a non-acid thermic family of Aquic Zerofluents, typically pale brown. The soil is highly permeable, somewhat poorly drained and has a very slow runoff factor. The principal associated soils are the Sacramento and Vena, and the competing Hanford, Sycamore, and Valdex soils. Thisarea was usually subject to periodic flooding prior to the construction of levees and other flood control measures. Effects of erosion are seen mainly due to the physical use of trails along the river bank. Erosion is also caused by strong boat wake action in the Mokelumne River creating continuing bank erosion and some tree loss along the eastern bank near Pig's Lake.
The Urban Geology Master Plan fo California lists the following characteristics for the project area: (1) low erosion activity, (2) low expansiveness rating of soil, (3) maximum expectable earthquake intensity is VI or VIII, minor to moderate damage, low severity, (4) ground water withdrawal-subsidence area, and (5) substantial aquifer recharge area.
Lowry and Associates of Sacramento completed an investigation of soil conditions in March, 1974 at the northwest end of Lodi Lake, to determine soil characteristics within the portion of the lake adjacent to the Mokelumne River, including classification, general bearing capacity and permeability. Three boring logs were compiled from samples taken near the peninsula area of the lake, which indicated tha