Orestimba Creek Feasibility Study - Stanislaus County

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Economics Appendix – Draft Report - Orestimba Creek Feasibility Study, Stanislaus County, California – September 2012 Orestimba Creek floodwaters eroded the west embankment of the Anderson Road bridge causing it to drop 2 feet in elevation and create several cracks in the bridge. In early February 1963, about 6 inches of rainfall over the Orestimba Creek basin caused both flooding and one of the largest peak flows of record. About 2,000 acres located 4 to 5 miles north of Newman were inundated by shallow floodwaters. Agricultural lands experienced soil erosion and silt deposition. The DMC siphon and access ramps to both road and railroad bridges were eroded to an extent that required repair. These floodwaters left debris that had to be removed. Extensive rainfall in January 1969 caused the flooding of nearly 2,000 acres. Flood damages occurred primarily on agricultural lands and consisted of erosion of agricultural soils, deposition of sediment, and prolonged field inundation which adversely affected area walnut orchards. In March 1995, Newman experienced the worst flood in the city's 107 year history. During the storm, the valley floor received between 2.5 and 4.0 inches of rain within 24-hours and more intense rainfall in the foothills. On March 10, 1995, the USGS gauging station located upstream from the California Aqueduct siphon registered a peak flow of 12,000 cfs. A convalescent hospital located on the north side of the city was entirely inundated by 2 feet of water in the building and 4 feet of water in the parking lot. Sixty-five residents were evacuated by a Medi- Flight helicopter after a failed attempt to use two ambulances and a school bus. Expansive areas of agricultural cropland were inundated by floodwaters. Additionally, a bean crop storage facility located just north of the city experienced extensive flooding affecting land and property forced the business into bankruptcy shortly after the flood. A neighboring agricultural packing facility also experienced flooding. During the 1995 flood event, many public streets and highways, including State Highway 33, were closed. These road closures limited or, in some cases, prevented access for emergency vehicles which resulted in diminished local and regional emergency response capabilities. Similar public health risks caused by area flooding included floodwater affected domestic water wells and individual septic systems, many of which were rendered unusable. In 1995, the city of Newman incurred reported flood damages of $7.8 million dollars (2011 prices). Additionally, a bean crop storage facility located just north of the city experienced extensive flooding affecting land and property that loss of $465,000 dollars and was forced the business into bankruptcy shortly after the flood. This facility closure resulted in lost wages and income for 14 employees and 20 to 25 local growers. Another agricultural packing facility experienced $400,000 dollars in losses. Many public streets and highways including State Highway 33 were closed that limited or prevented access for emergency vehicles resulting in diminished emergency response capabilities. Flooding that affected domestic water wells and septic systems rendering many unusable also increased public health risks. Actual damages incurred from the 1998 flood are not known. The actual monetary cost of flood damages incurred by private property owners in West Stanislaus County during the most recent floods of record are difficult to fully assess. There are 2
Economics Appendix – Draft Report - Orestimba Creek Feasibility Study, Stanislaus County, California – September 2012 few written records on historical floods in the cities of Patterson and Newman and in the predominantly agricultural lands of Stanislaus County. Property owners have taken care of their own flood damages without assistance from the Federal Emergency Management Agency. Therefore, the historical record is not a good reference point for baseline economic damages. Due to the relatively shallow depths of flooding, sandbagging and other flood-fighting methods have also helped to truncate damages incurred. 1.4 Methodology (References and Methods Cited) This economic analysis is in accordance with standards, procedures, and guidance of the U.S. Army Corps of Engineers. The Planning Guidance Notebook (ER 1105-2-100, April 2000) serves as the primary source for evaluation methods of flood risk management studies and was used as reference for this analysis. Additional guidance for risk-based analysis was obtained from EM 1110-2-1619, Engineering and Design – Risk-Based Analysis for Flood Damage Reduction Studies (August 1996) and ER 1105-2-101, Planning Risk-Based Analysis of Hydrology/Hydraulics, Geotechnical Stability, and Economics in Flood Damage Reduction Studies (March 1996). Economic evaluation was performed over a 50-year period of analysis. All values are presented in October 2011 price levels, and amortization calculations are based on the Fiscal Year 2012 federal discount rate of 4.0 percent as published in Corps of Engineers Economic Guidance Memorandum (EGM). 3
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Orestimba Creek Feasibility Study - Stanislaus County

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