SJAFCA SPECIAL BOARD MEETING SEPTEMBER 11, 2017

Transcription

1 SJAFCA SPECIAL BOARD MEETING SEPTEMBER 11, 2017

2 Mormon Channel

3 History In the early 1900 s the U.S. Army Corps of Engineers constructed a dam across Mormon Slough upstream of Gillis Road and excavated the Stockton Diverting Canal to the Calaveras River. In the early 1950 s, a concrete drainage culvert was constructed along the Lower Mormon Channel from Wilson Way to Commerce Street with the intent of reclaiming the Channel bed for development. However, the floods of the early 1950 s prompted the City Council to adopt Section of the Stockton Municipal Code, prohibiting filling within the banks of Mormon Channel thus protecting it as a floodway. In 1955, flood flows overtop the Diverting Canal entered into and soon overwhelming Mormon Channel Flooding south of Mormon Channel.

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7 EXPERTS SAID FLOOD WOULD NEVER HAPPEN IN STOCKTON First Time in History So Much Rain Fell in Short Space, City Manager Says Stockton was flooded by water which the experts said would never come. It was the first time in history that much water has fallen in such a short space of time, City Manager John Lilly reported today in explaining the flooding of the Mormon Channel. The Diverting Canal was designed specifically to divert water from Mormon Channel which branches off from the Calaveras River, back into the river north-east of Stockton. Mormon Channel overflowed at Gillis Road and sent water spilling into Stockton. The Diverting Canal held firm on the city side, but broke and flooded to the east. But there was never a prediction that an estimated 6 inches of rain would fall to combine with near capacity flow from Hogan Dam. It was this combination which sent water spilling into South Stockton.

8 CITY ASKS U.S. CHANNEL FUND Request for a 3 million dollar Federal appropriation for the construction of a depressed freeway and flood raceway in Mormon Channel was made in a telegram sent yesterday by City Manager John C. Lilly to Rep. Leroy Johnson s office in Washington. The request stems from last weekend s disastrous floods in Stockton when the Mormon Channel overflowed its banks and inundated large areas of the city.

9 History In 1958, the City conducted a hydraulic study and preliminary flood channel design to determine the right of way needed for a channel with a flood carrying capacity of 3000 cubic feet per second (cfs). The 3000-cfs represented the reasonable maximum flood flow expected in Mormon Channel below the Diverting Canal. The 1958 study was to function as a Master Plan for the development of Mormon Channel. Further studies were recommended to determine the precise alignment and design of the Channel.

10 History In 1963 New Hogan Reservoir was completed In 1962, a Federal flood control project for Mormon Slough and the Diverting Canal was authorized to increase the flood capacity of the Diverting Canal and improve flexibility in operating New Hogan flood control releases. Completed in 1970, by the Corps of Engineers, this project raised the south levee of the Diverting Canal which further blocked flows into the Mormon Channel from Mormon Slough. Since completion of this project, Lower Mormon Channel has provided local drainage only. In 1969, CalTrans realigned a portion of Mormon Channel in conjunction with the construction of the Crosstown Freeway. In 1970, following the CalTrans realignment of the Channel, the City Council adopted a specific plan for the Mormon Channel between Taylor and Sutter Streets based upon a design capacity of 3000 cfs.

11 History Two Public meetings were held in April Concerns from the public included: Agricultural representatives asserted that water on the east side of the County is needed for agriculture and should not be used for the project. A petition signed by eighteen farmers along the area who are against the project and its potential impacts Comments from adjacent property owners that the channel needs to be cleaned up. The Mormon Channel diversion would provide significant flood control benefit Citizens were concerned about recreational trails that might generate potential nuisances like trespassing, littering, dumping, horseback and motorcycle riding.

12 History A Special SJAFCA Board meeting was held on May 1, 2002, to discuss SJAFCA s continued interests in improving Mormon Channel. The Phase II Study evaluated 14 flood control measures and after screening only the lower Mormon Channel Project remained The Mormon Channel Project would provide approximately a 250-year level for the Stockton Diverting Canal and Calaveras River It was determined that the use of Phase I Assessment District funds could not be used for a Mormon Channel Project The Board took action and resolved that no further interest in proceeding with a Mormon Channel Study.

13 Mormon Channel The Lower San Joaquin River Feasibility Study included improving both a Mormon Channel Bypass and the Diverting Canal A cost estimate was prepared for a Mormon Channel Bypass The Corps removed both from the Study due to their Benefit/Cost determination. While both the State and SJAFCA continued to encourage the Corps to include the improvements in the preferred alternative the Corps did not include in the Selected Alternative. A Mormon Channel Bypass continues to have State support and is represented in both the State s San Joaquin River Basin-Wide Plan and the 2017 CVFPP. Locally the Mormon Channel Bypass is included in the Regional Flood Management Plan.

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15 Mormon Channel Today Putting flows back into Mormon Channel could reestablish a diverse habitat in Mormon Channel. These improvements could also include nature trails and bike paths. Redirecting flood flows from the Diverting Canal into a controlled Mormon Channel bypass could reduce the potential for flooding in Stockton. This would lower the flood flows in the Lower Calaveras River and Diverting Canal. Costs are estimated at $50 million to reestablish Mormon Channel to carry flood flows and construct a flood flow control structure. Costs includes $14 million for R/W

16 Challenges

17 Challenges

18 Mormon Channel Flood Bypass The Diverting Canal and Calaveras River can currently carry a 100-year flows (15,700 cfs). By removing 1500 cfs from the Diverting Canal the Calaveras System would now be capable of carrying an event larger than a 200-year event. Other improvements would be needed to meet State 200-year system standards.

19 Mormon Channel A Mormon Channel Bypass $50 million costs did not include an O&M assessment to maintain the channel and flood control structure Challenges Funding (State) Local Assessment District Environmental Public support Possible Solutions Obtain State assistance from a future State Flood Bond(local match needed) After funding obtained prepare full environmental evaluation Include in the local effort of a 200-year fix for upper portion of the Lower Calaveras and Diverting Canal

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