SAN JOSE CAPITAL OF SILICON VALLEY

Transcription

1 Attachment A CITY OF ffr SAN JOSE CAPITAL OF SILICON VALLEY STORM SEWER SYSTEM ANNUAL REPORT FY Installation of Large Trash Capture Device October 2016

2 City of San Jose Storm Sewer System Annual Report FY CONTENTS. 1 I. HISTORY AND BACKGROUND 3 II. PROGRAM FUNDING 5 A. Adopted FY CIP Budget Revenue 5 B. Adopted FY CIP Budget Expenditures 5 C. Adopted FY Operations and Maintenance Budget Expenditures 5 III. PROGRAM ACTIVITY 6 A. Storm Sewer Improvement Projects 6 B. Rehabilitation Projects 8 C. Existing Storm Pump Stations 9 D. Non-Construction Activities 10 E. System Management and Planning Master Planning 10 a. Alviso and North San Jose Master Plan 10 b. Modeling for Flooding Areas 12 c. DOT Portable Pumping Operation for El Nino Season 15 d. Flow Monitoring 15 e. Modeling Coordination with Water District and Alameda County 15 f. Citywide Storm Drain System Master Plan Initial Results Support Economic Development Coordination with Santa Clara Valley Water District (District) Neighborhood/Special Corridors Rehabilitation of Pump Stations Improving Annexation Areas San Jose-Santa Clara Regional Wastewater Facility. 25 E. Sustainability/Green Vision 25 VI. OPERATIONS AND MAINTENANCE 27 V. CONCLUSION

3 I. HISTORY AND BACKGROUND The City of San Jose drains to two main water shed/drainage basin areas, Coyote Creek and Guadalupe River. Within the tributary areas to these watersheds, the majority of the City's storm sewer collection system benefits from the generally uniform topography of the Santa Clara Valley, allowing the majority of the water to be conveyed to the waterways using gravity lines with minimal use of pump stations. The City's storm sewer network is a storm water collection system that includes more than 1,100 miles of storm sewer pipelines, 32,200 storm drain inlets, 1,510 storm outfalls, and over 4,500 miles of curb and gutter. Various channels, culverts, ditches, detention and debris basins make up the remainder of the system. The storm sewer system is designed to convey storm water away from developed areas to local creeks and rivers, and ultimately, to San Francisco Bay. An estimated 67 percent of the City's storm drainage system was constructed between 1950 and Levees separate North San Jose from Coyote Creek and the Guadalupe River. These levees enable water levels in both waterways to rise to elevations higher than adjacent lands in North San Jose. In those instances, pump stations are needed to discharge storm runoff into the waterways. In the absence of pump stations, internal flooding would likely occur in various portions of North San Jose. The City owns and operates 30 storm pump station with various capacities, including the Cahill Pump Station recently relinquished to the City and previously operated and maintained by Caltrans and the Berryessa Pump Station constructed for the Flea Market Development. The larger pump stations drain areas located north of Highway 101 into the Guadalupe River. The smaller pump stations typically drain street underpasses. The construction dates of the smaller pumps range from 1928 to 1975, the majority of which are over 40 years of age. Since the mid 1980's, the City's design standard requires that storm sewer systems be designed to convey a 10-year storm event (a storm large enough to have a 10 percent chance of occurring in any year). The 10-year event is widely recognized as a reasonable, safe standard, and is employed by numerous jurisdictions nation-wide. Prior to 1990, approximately 67 percent of the storm drains were designed for a 3-year storm event standard. In many areas that have been annexed to the City, the capacity is even less than a 3-year event. While all new developments are required to design their on-site storm system to accommodate a 10-year event, they are not required to address deficiencies of the downstream storm sewer system to which the developer connects. The Department of Public Works designs and builds storm sewer infrastructure funded through the City's Capital Improvement Program. Public Works also reviews and inspects storm sewer improvements constructed by private developers and other public agencies. The Storm Section is part of the Transportation & Hydraulics Services Division in Public Works. The Storm Section is tasked with the design and construction of improvements that maximize the efficiency of the existing storm sewer system to meet current and future needs, the design and construction of improvements that rehabilitate older deteriorated storm sewers and storm pump stations to extend useful life, design and construction of green infrastructure and trash reduction methods for stormwater quality improvements as required by regulatory agencies, master-planning of the City's storm sewer system to meet the future demands for conveyance, identifying and prioritizing the City's storm sewer capital investments, rehabilitation program and corrective maintenance activities. 3

4 The Department of Transportation performs day-to-day operations and maintenance of the collection system. The Environmental Services Department is responsible for protecting the health of the South Bay watershed through regulatory programs that prevent pollution from entering the storm sewer system and waterways. Citywide Watershed Map 4

5 II. PROGRAM FUNDING A. Adopted FY CIP Budget Revenue Primary sources of funding include transfers from the Storm Sewer Operating Fund, the Storm Drainage Fee, interest earnings, and joint participation revenues. The Storm Sewer Operating Fund provides funding for capital improvement projects and the federally mandated National Pollutant Discharge Elimination System requirements through Storm Sewer Service Charge fees. Storm Drainage Fee (Fund $446,175) - Storm Drainage Fees are charged to developers for the privilege and benefit of land directly or indirectly discharging into the storm drainage system, and also for the benefits accruing to said land because of the existence of a city storm drainage system which collects and disposes of waters from other lands in the city. The fees collected may only be used for the construction, reconstruction and maintenance of the storm drainage system for the City of San Jose, and for acquisition of land for such system. The fee is based on land use and acreage. Storm Sewer Capital Fund (Fund $30,582,491) - Funds for capital improvement projects are transferred from the Storm Sewer Operating Fund (Fund 446) and from the California Proposition 84 Storm Water Grant Program (SWGP) and Integrated Regional Water Management (IRWM) Implementation Grant Program. These funds are used for new or rehabilitated pump stations, new or replacement laterals, pipe, storm drain inlets, outfall rehabilitation, and projects that address water quality issues. Joint Participation Revenues ($4,000) - This revenue comes from the City of Cupertino, when, in the late 1970s, City boundaries were redrawn and a portion of Cupertino's storm sewers system connects into San Jose's system before being conveyed downstream. This revenue covers maintenance and operations expenses for Cupertino's share of the system. B. Adopted FY CIP Budget Expenditures The Storm CIP Program has a $52.3 million, 5-year budget. This level of funding allows three to four medium neighborhood improvement projects to be completed each year. It is important to note that the current level of funding in the Storm CIP program only addresses immediate needs for dealing with minor neighborhood drainage issues. It does not address long-term, system-wide needs stemming from significant development activities that have occurred over the past few decades and those planned for future years. The on-going Master Planning effort will provide a working document that establishes city-wide long-term solutions for any deficiencies or lack of efficiency within the storm sewer system. C. Adopted FY Operations and Maintenance Budget Expenditures (Fund 446) - The annual ongoing operating and maintenance budget is approximately $8.2 million which provides funding for administration, engineering and maintenance. 5

6 III. PROGRAM ACTIVITY A. Storm Sewer Improvement Projects A portion of the Storm Section's resources are allocated to the Storm Capital Improvement Project (CIP) Program for resolution of localized drainage problems, primarily in residential neighborhoods, neighborhood business districts and school zones. These projects typically address localized ponding and neighborhood drainage issues that can be corrected by extending or enhancing the existing storm sewer system. Improvement projects for fiscal year include the following: Wilson Avenue and The Alameda - Public Works General Engineering Contract for Underground Pipe Facilities (CPMS ID 7660) During the potential threats of El Nino, this project was identified by local residents who were experiencing significant localized flooding issues and notified the City to address improvements to the existing drainage system in this area. This project and Stockton Avenue and Lenzen Avenue project (later discussed in this report) are within existing storm drainage systems that are under significant capacity. As a result, the storm master plan team evaluated and determined major deficiencies in the Q2,08ja-i.gaBg storm sewer system that should be implemented to help minimize and/or eliminate flooding in this area. Two large hooded inlets and two flat grate inlets with laterals were installed. The total construction cost of the project was $56,727 and the contractor under this General Engineering Contract was JMB Construction and was completed on February 9, Warner Drive - Public Works General Engineering Contract for Underground Pipe Facilities (CPMS ID 7660) A resident notified the City that during previous wet season a significant amount of stormwater from Warner Drive enters onto the resident's property that is located along the easterly downslope side where the roadway curves. The resident was very concerned about the potential threats of El Nino and was seeking the City's assistance. City evaluated the existing drainage area and determined that this resident's house was at the low point along the vertical profile of Warner Drive and resolved the issue by extending a portion of the storm sewer main to install new inlets and laterals to minimize the amount of storm water runoff onto this resident's property. 6

7 Approximately 140 linear feet of 15 inch RCP storm sewer pipe, one manhole and two regular hooded inlets with laterals were installed. The total construction cost of the project was $115,666 and the contractor under this General Engineering Contract was JMB Construction and was completed on April 15, Joseph Avenue and Curtner Avenue - Public Works General Engineering Contract for Underground Pipe Facilities (CPMS ID 7660) Last winter, due to the potential threats of El Nino, this project was identified by residents in the surrounding area that indicated localized flooding. Based upon upon the storm sewer modeling of existing conditions, the storm sewer system in this area experiences localized flooding when the outfall is submerged in the due to the rising water levels in Coyote Creek. This project installed 90 linear feet of 15 inch RCP pipe, manhole and two regular hooded inlets with laterals were installed to help reduce the localized flooding. The total construction cost of the project was $111,873 and the contractor under this General Engineering Contract was JMB Construction and was completed on March 11, Stockton Avenue and Lenzen Avenue- Public Works General Engineering Contract for Underground Pipe Facilities (CPMS ID 7660) This project was identified by local residents who were experiencing significant localized flooding issues and notified the City to address improvements to the existing drainage system in this area. As a result, the storm master plan team evaluated and determined major deficiencies in the existing storm sewer system that should be implemented to help minimize and/or eliminate flooding in this area. Due to a lack of storm sewer pipe system, many of the properties installed curb side pipes to drain towards the street curb and gutter. There were minimal amount of existing inlets installed along Lenzen Avenue and Stockton Avenue. As a result, the low point on the street was located near Pershing Avenue and Stockton Avenue. Based upon visual inspection and storm master plan model results, it was evident that this area experience significant amount of localized flooding that exceeded past the sidewalk onto the private property. This project installed three large hooded inlets with laterals and two manholes along Lenzen Avenue and Stockton Avenue to the stormwater to enter into the storm sewer system as quickly as possible. 7

8 The total construction cost of the project was $80,880 and the contractor under this General Engineering Contract was JMB Construction and was completed on March 25, Piedmont Hills High School - Public Works General Engineering Contract For Underground Pipe Facilities (CPMS ID 7660) This project was identified by Santa Clara Valley Water District (SCVWD) when a sinkhole was discovered within SCVWD property that is adjacent to stand seats near a football field on Piedmont Hills High School campus in east San Jose area. The sinkhole was in vicinity of a 48-inch City owned corrugated HDPE pipe. The Department of Transportation excavated a portion of the area to determine that the 48-inch corrugated HDPE storm sewer main was disconnected to the Santa Clara Valley Water District 54 inch flood control storm pipe. This was an urgent repair that needed to be accomplished prior to graduation on Piedmont Hills High School campus. The total construction cost of the project was $44,686 and the contractor under this General Engineering Contract was JMB Construction and was completed on May 25, B. Rehabilitation Projects Alviso Storm Network Infiltration Control This project was one of the first storm sewer condition assessment projects that Public Works managed and modeled this project similar to the sewer program. The Alviso area was chosen since it was prone to flooding and City has established annual funding for condition assessment appropriation has been established to regularly clean large diameter pipes in areas that are prone to flooding. This project required CCTV inspection and cleaning of approximately 11,000 feet of storm sewer mains from 24-inches up to 48-inches in diameter in the Alviso area. The results will be used to establish a database for prioritization and development of future storm sewer repairs and rehabilitation projects and any structural defects will be corrected immediately. 8

9 C. Existing Storm Pump Stations The average age of the City's 30 storm sewer pump stations is approximately over 40 years. These facilities are listed in Table 1 shown below. The existing pump stations at Oakmead, River Oaks, Rincon I, Rincon II and Gateway were evaluated for adequate capacity using the 10-year storm event. Pump stations are generally considered adequate if there is sufficient pump capacity to discharge design runoff into the receiving waters or if excess flows can be stored without causing property damage. The master plan recommended existing pump station improvements to increase reliability and redundancy, and to comply with FEMA flood hazard mapping requirements. These projects include installation of on-site backup power at the Rincon I, Rincon II, and Gateway Pump stations, and the replacement of pumps at the Oakmead Pump Station. Table 1: Storm Sewer Pump Stations (Alphabetical Order) Name Year Built Year Updated/Status Pump Stations 1. 87/Taylor 2005 N/A 2. Airport 1990 N/A 3. Alma Almaden Bascom 1958 N/A 6. Bird Capitol 1990 N/A 8. Communication Hill 2009 N/A 9. Chynoweth 1988 N/A 10. Delmas Forest Gateway Gold Golden Wheel 2001 N/A 15. Hedding 1960 N/A 16. Hester 1928 N/A 17. Hope Street N/A 18. Hope Street N/A 19. Julian 1975 N/A 20. Liberty Oakmead Park Rincon N/A 24. Rincon N/A 25. River Oaks Skyport 2005 N/A 9

10 27. Taylor 1939 N/A 28. Willow Berryessa (Flea Market) 2016 N/A 30. Cahill (in progress) D. Non-Construction Activities Non-construction activities for the Storm Sewer Section include oversight of storm sewer program management, Preliminary and Final Engineering design, construction management, updating GIS information, Storm Sewer Master Planning, Storm Sewer Permit Review and Inspection for Development and Outside Agencies, Public Art, Fee Administration, plan review for other sections and Divisions of Public Works, representing approximately $3,072,000. E. System Management and Planning 1. Master Planning a. Alviso and North San Jose Master Plan The North San Jose Storm Drain Master Plan for North San Jose Development Policy and Alviso areas was completed and a final report was prepared by Schaff and Wheeler in June The Master Plan evaluated the storm drain system capacity under existing and 2040 General Plan land use conditions. A computer model using MIKE-URBAN software was developed to simulate the hydrology and hydraulics of the drainage system and to identify capacity deficiencies at a 10-year 24-hour design storm event. The master plan identified minor, moderate and severe pipe deficiencies with reference to the predicted depths of street flooding caused by the deficient pipes. For minor deficiency, flooding depth would be less than 6 inches; for moderate deficiency, between 6 and 12 inches; and for severe deficiency, deeper than 12 inches. Drainage system deficiencies for both existing and 2040 General Plan land use conditions were identified. The Master Plan recommended 55 improvement projects totaling approximately $131 million for flood protection. Among these projects, twelve (12) projects totaling close to $57 million are high priority projects. This study and the proposed CIP is a starting point. PW will perform a more detailed master plan study to confirm the project limit and sizing, and conduct alternative analysis to find more affordable or effective improvements with information gathered as part of the design process. As part of the citywide storm drain master plan study, North San Jose and Alviso systems will be included in the InfoWorks ICM model. Future capacity analysis of the storm drain system will be performed using this modeling tool. 10

11 Alviso Area The Alviso area model network included storm drain pipes of 12 inches in diameter or larger, with 294 manholes and 28,600 feet (5.4 miles) in length. The hydraulic model predicted flooding at over 180 manholes, of which about 100 manholes was predicted with more than 6 inches of flooding depth at a 10-year storm event. The computer model confirmed known flooding locations, such as the most commonly flooded area at the intersection of Hope and Catherine Streets, and at the low-lying areas around Gold Street and Taylor Street. In addition to identifying storm drain capacity improvements for the 10-year storm event, the master plan recommended improvements to alleviate the flooding impact due to interior system deficiencies at the 100-year event for 2040 General Plan land use scenario. The urgent need for the Gold Street Pump Station to be upgraded to 110 cubic feet per second (cfs) from the existing 30 cfs pumping capacity was confirmed. The study also recommended approximately 3,700 feet storm drain pipeline to be upsized or constructed new in order to minimize 100-year street flooding. North San Jose Development Policy Area Drainage pipes 15-inch in diameter and larger which accounts for more than 35 percent of approximately 49 miles of pipes in the study area were included in the hydraulic model. The North San Jose Policy Area is mostly occupied by pre-existing developments, with over 65 percent industrial land uses, but less than 10 percent open space/vacant land. The average percentage of impervious surface of existing developments is high and estimated at 80 to 90 percent. And the 2040 General Plan land use in North San Jose will likely maintain high percentage of impervious surface. Stormwater runoff from the North San Jose is conveyed through storm drain networks and discharged to two channels, Coyote Creek and Guadalupe River. North San Jose's storm drain system is broken into five general drainage areas: Oakmead, River Oaks, Rincon/Charcot, East Coyote, and Brokaw. The master plan study confirmed known flooding areas such as Charcot Avenue, Zanker Road, and Brokaw Road areas. The master plan also confirmed the need for a 300 cfs Charcot Pump Station previously identified in the 1999 North San Jose Storm Drain Master Plan Report. Most of the severe flooding would occur in Rincon/Chacot area and the area east of Coyote Creek. The master plan recommended 47 CIP projects to provide flood protection for areas with storm drain capacity deficiencies. The projects were prioritized based on the severity of deficiencies. These projects include new or upsized pipelines, outfalls, new pump stations in Alviso and Charcot areas, and upgrade of existing pump stations for reliability and compliance with FEMA flood hazard mapping requirements. Storm Sewer System Annual Report-FY

12 Out of the 47 storm drain system improvement projects, 42 are needed to address street flooding under existing land use conditions. Some of these 42 projects are sized to address increased flooding due to future land use growth. Approximately 113,000 feet of pipeline construction have been recommended for long-term 2040 General Plan land use condition, with 102,000 feet needed to minimize street flooding for existing conditions. Total capital improvement program for the North San Jose Policy Area will cost approximately $113 million, with roughly 40 percent or $45 million needed for high priority capital improvements. b. Modeling for Flooding Areas PW Master Planning Staff performed modeling analysis as requested by DOT for the historical known flooding areas. The preliminary model was used at the time of the analysis and the results are presented below for the Charcot/Zanker, Alviso, and Stockton/Taylor areas. Charcot/Zanker Area The storm drain system in the Charcot area collects serves approximately 500 acres that drains through the intersection of Charcot Road and Zanker Road and outfalls to Coyote Creek. This is opposite of ground slope with the highest at point Coyote Creek. In a large storm event, water cannot drain by gravity from the Charcot area into the creek because the creek's water level is higher than the level of the adjacent land. This causes the outfall structure's flap gate to close, forcing water to back out of drainage system in the lower portions of the Charcot area, resulting in street flooding. Recently, the December 11,2014 storm backed up the existing storm sewer system and flooded intersections, parking lots and a nearby business. Staff performed hydraulic modeling for this area using the latest InfoWorks model to identify temporary and long-term solutions to minimize flooding. The model indicates that the 42- and 48- inch system between Junction Avenue and Zanker Road has a limited capacity of 8 to 16 cfs, although the downstream pipes can convey up to 84 cfs. With the results from the hydraulic model and field experience, PW worked with DOT and Santa Clara Valley Water District to set up a total of three 12-inch portable pumps (one 12-inch pump was used for redundancy) to handle approximately 22 cfs for this area that will help shorten the flooding time and reduce the flooding depth, even though it would not provide total relief to the area for the 10-year event. For this reason, constructing a new 300 cfs Charcot Pump Station has become a high priority improvement that will pump stormwater from the Charcot area to the Coyote Creek. The master plan study indicated that all high priority projects are needed to solve existing capacity deficiencies, and over 80 percent, or 8,600 out of 10,400 feet of high priority pipeline improvements are located in this area. Approximately $37 million is needed for the high priority improvements for the Charcot area, including the construction of a new 300 cfs pump station. Alviso Area The storm drain system in Alviso has a primary pump station at Gold Street with a pump capacity of 30 cfs. The station can keep up with a small storms similar to a 2-year event. Under a larger storm, the pump station would be overwhelmed and stormwater would be back up and begin to 12

13 pond and flood at low-lying areas. DOT is deploying portable pumps at Archer Street/State Street, Liberty Street/State Street, and Hope Street/Catherine Street when rainfall intensity is predicted to be greater than a 2-year event. To prepare for the El Nino season in the winter of 2015/2016, staff evaluated the Alviso storm drain system using the Info Works model to identify an effective temporary pumping plan for up to a 10-year storm event and a backup pump deployment plan when rainfall intensity increases. After considering the result from the modeling analysis and the field experience from storm drain maintenance crew, DOT concluded that the existing standard portable deployment plan will be suitable for a small flooding causing storm event, and that a backup plan would include additional pumps at Gold Street/Catherine Street and immediate upstream of Gold Street Pump Station. The number of portable pumps at these locations may increase to keep up with greater rainfall intensity. The long-term solution to alleviate the street flooding in Alviso area is to construct the 110 cfs pump station near Gold Street and Catherine Street. Upsizing the existing Gold Street Pump Station was not feasible for two reasons (1) lack of area on the existing pump station property to build a new 110 cfs storm sewer pump station and (2) the duration to construct a new 110 cfs storm pump station would require the decommission of the existing storm sewer pump station. The new storm pump station will have the pumping capacity to handle the 100-year event. The City is in the final design and permit phase for a new 110 cfs Alviso Storm Sewer Pump Station and force main project. The City intends to keep the existing Gold Street Pump Station operating during the construction of the new pump station. The old Gold Street Pump Station will be used as a backup pump station after the new pump station is built. The design started in April 2014 and it is anticipated to award in April 2017, pending environmental permitting approval from regulatory agencies. The project construction is anticipated to complete in Stockton/Taylor/Cinnabar Area Also during the December 11, 2014 storm, DOT experienced several flooding issues near Cahill pump station and Taylor Street underpass. Staff began to further evaluate the existing system to understand the capacity constraints. There are 18-inch and 30-inch storm mains on Taylor Street and Stockton Avenue that serve approximately 270 acres and eventually discharges through an existing 8 ft. by 3 ft. outfall culvert to the Guadalupe River. A pump station with 4.4 cfs capacity was installed to provide drainage for the Taylor underpass. In the 1970s, a 30-inch pipe was constructed at Schiele Avenue to supplement a parallel existing 16-inch storm drain, and a 30-inch stubout was built at Stockton Avenue, possibly for future improvements further downstream. However, the extension was never been constructed along Stockton Avenue. Public Works conducted a preliminary computer hydrologic and hydraulic modeling analysis of the system using the May 14, 2015 storm. The model showed that the system could convey a 2- Storm Sewer System Annual Report-FY

14 year event with a capacity of approximately 35 cfs. But the May 14, 2015 storm event would generate more than 77 cfs of stormwater runoff from the Stockton-Taylor drainage area. The model confirmed the flooding at Pershing Avenue and Taylor underpass that was observed by DOT and residents. Also, Public Works installed three flow meters in these systems during the El Nino season: GUA34 at Stockton/Villa Avenues, just upstream of the Stockton/Taylor intersection, GUA 31 at West Taylor and Irene Streets, approximately 1,000 feet upstream of outfall, GUA_32 at Cinnabar and Montgomery Streets. The flow monitoring data confirmed the model results and field observations. South of the Stockton-Taylor system is the Cinnabar-Stockton-West Santa Clara-Cahill Pump systems. The Cahill Pump Station was constructed by the State in 1939 with 4.4 cfs capacity for the underpass drainage and has sufficient capacity to address a 10-year rainfall event. The station was last rehabilitated in 1975 and the current pumping system is in need of replacement. The Cahill PS rehabilitation project will began in summer 2016 with anticipated completion in February 2017 to replace the two existing pumps and install a diesel powered emergency pump. Both the Cinnabar-Stockton system and West Santa Clara system are at a 2- to 3-year design. During the May 14, 2015 storm, this system was greatly surcharged and flow was backed up to the intersection of the Alameda and Stockton and caused flooding. The flooding at the Cinnabar/Stockon area would further compromise the Stockton-Taylor system as shown in the hydraulic model, due to the topography on Stockton Avenue generally sloping down northwesterly. The capacity improvement alternatives for this area were evaluated. The most cost-effective solution would be to construct a 54-inch storm drain on West Julian Street from Stockton Avenue and connect to the existing 54-inch Julian pipeline and the outfall system, and to construct a 30- to 54-inch pipe on Stockton between Schiele and the Alameda to convey stormwater to Julian. The project would involve approximately 4,500 feet of new pipe. Some remaining flooding at Taylor/Stockton intersection can be alleviated through a 2,300 foot, 30-inch diversion pipe from this intersection to the Hedding Street system at Elm Street. Potential utility conflicts or constructability issues under UPRR/Caltrain crossing will need to be further evaluated. The model showed that the drainage capacity is not only limited the pipeline system, but also further reduced when the river flow level rises above the outfall. According to the Santa Clara Valley Water District's HEC-RAS model, the river elevation at the Taylor outfall would be at 58 feet at a 2-year event and would reach 61 feet at a 10-year event. Currently, the top of the outfall opening is at 53 feet, thus the outfall would be submerged during a small storm event. A pump station may be required as part of the capacity improvement for this system, and will be evaluated with the master plan study. 14

15 Funding to design and construct the improvement is not available in the current 5-year CIP. DOT and PW staff are re-evaluating the existing maintenance and operation practice to identify options to provide temporary relief. c. DOT Portable Pumping Operation for EI Nino Season Although the total rainfall was greater than that of an average year, there were no large storm events during the El Nino season. The biggest storm events occurred on January 6, 2016 and March 3, Both storms had less than 1.3 inches of rain in a 24-hour period and could be categorized as less than a 1-year event. During this El Nino season, in addition to the temporary pumps that were installed at Cahill Storm Pump Station, PW installed a total of three 12-inch temporary pumps at the Charcot/Coyote Creek location. DOT deployed the pumping plan in Alviso, however none of the three locations experienced significant flooding. d. Flow Monitoring Flow monitoring is an essential component of hydraulic modeling from which flow and rainfall data are collected for the calibration and verification of the H&H model. The storm events of 11/19/13, 2/6/14 and 2/26/14 were the largest storm events during the wet season and were used for model calibration. However, these events were small and were less than 2-year return frequency, and little or no pervious area runoff would be resulted from these storms. Therefore, a second season flow monitoring was needed at most of the original sites and a few alternate locations to the unsuitable first season sites. Total of 75 flow meters measuring depth and velocity were installed by mid-october 2014 and additional 10 flow meters were installed in January The rainfall measurement system also included 25 rain gauge sites for the wet weather season between October 2013 and April During this period, the meters collected flow data for a very large storm on December 11, This storm was measured as a 10- to 50-year event for the 24-hour duration at various locations in the City. This storm was used to calibrate the pervious area runoff generating parameters. During the El Nino season, staff deployed 80 flow meters and 16 rain gauges throughout the storm drain system for from October 2015 to April 2016 to capture flow data in the storm drain system. The biggest storm events occurred on January 6, 2016 and March 3, 2016 with less than 1.3 inches of rain in a 24-hour period. These less than 1-year return frequency events were not used for model calibration. e. Modeling Coordination with Water District and Alameda County The City has been coordinating and collaboratively working with the Santa Clara Valley Water District (District) on the modeling effort and data needs. The Water District is responsible for the modeling of the county's river/creek system, and the City is responsible for the modeling of the City's urban drainage pipeline and pumping systems. The two agencies and the neighboring Alameda County Flood Control District worked together to share the knowledge and experience in stormwater runoff volume and routing 15

16 methodologies, loss method, land use percent impervious, and other parameters for hydrologic and hydraulic (H&H) modeling. The City integrated District's riverine system model City's Infoworks ICM storm system model and used the District's stream gauge and high water mark data to verify the integrated H&H model. The City has also applied the District's recently modified design rainfall depth equations for the design storms for the master plan study. Collaboratively, the City provided the calibrated urban drainage model and other related data to the District for their recent Lower Silver Creek and Berryessa/Penitencia Creeks floodplain studies. The collaboration between the City and the District has the cost-saving benefit to both agencies, and allows each agency to focus on their respective studies. f. Citywide Storm Drain System Master Plan Initial Results Hydrologic and Hydraulic (H&H) Model of Storm Drain System The citywide storm drain system's dynamic H&H model was developed using the InfoWorks ICM (integrated catchment model) software. The model included pipes 24 inch and larger using City's GIS datasets, as-builts and survey data, and incorporated the Water District's HEC model files into the H&H model. The model included over 40 percent of the storm drains or over 540 miles of pipeline system, 634 outfalls, 29 pump stations, and over 180 miles of river/creek system. All LID (Low Impact Development) and HM (hydro-modification) projects currently installed and documented were included in the H&H model LID features and 7 HM facilities total. Figure 1 shows the pipe, pump station and outfall network included in the model. 16

17 Model Pipes Model Outfalls Model Pump Stations Guadalupe Watershed Coyote Watershed San Thomas Aquino Watershed GIS Pipes GIS Outfalls GIS Pump Stations City Service Area Creeks Figure 1: Urban Drainage System Included in the H&H Model 17

18 Three major watersheds, Guadalupe River, Coyote Creek, and San Tomas Aquino/Calabazas Creeks, over 580 square miles of drainage area was included in the H&H model, with approximately 20 percent of it inside City's Urban Growth Boundary (UGB). The drainage area was delineated into 7,000 sub-catchments, with sizes ranging from less than one acre to over 1,000 acres. Inside UGB, average sub-catchment size is around 14 acres; and outside UGB, average is over 500 acres. The drainage size, land use type and associated percent of impervious, soil type, initial loss, and other hydrologic and hydraulic factors were included in each sub-catchment for computation of runoff flow responding to rainfall. Through collaborative effort, City staff and the Water District worked out the methodologies for runoff calculations and percent of impervious area values for various land use types. Both agencies will use the same methodologies in future modeling studies of urban system. Calibration and verification were performed to validate and verify the model's accuracy. Calibration methodology included applying actual rainfall events to the model and adjusting the model parameters so that the resulting flows match the measured flows. Rain and flow data for two wet seasons ( and ) were used for the calibration. In addition, the calibrated model was validated using observed creek levels, and flooding data and complaints for recent storm events. Existing System Performance at Existing Flow Conditions The calibrated model was run for 3- and 10-year 24-hour design storm events to review existing system deficiencies. The 15-minute interval design storms based on the Water District's design storm depths were selected for the master plan study. Preliminary Model Results for the 3-year Design Event The model of the 3-year design event predicted flooding at 550 manholes (out of 13,700 manholes modeled) or about 3.7 percent of the modeled system located in Guadalupe, 115 in Coyote, and 75 in San Tomas Aquino and Calabazas watersheds. Maximum flood depth of 6 inches or deeper were predicted at 170 manholes, or roughly 1 percent of the modeled system. Figure 2 presents the model results of the 3-year design storm event. The H&H model also showed storm drain deficiencies (at full-pipe capacity) for existing system flow at 13 percent of the pipes. But if all bottlenecks were improved to provide free flow conditions, roughly 22 percent of the existing storm drain would become deficient at the resulted unrestricted flow. Preliminary Model Results for the 10-year Design Event For the 10-year 24-hour design storm event, the H&H model predicted flooding at 1,770 manholes or about 12.6 percent of the modeled system in Guadalupe River, 440 in Coyote Creek, and 160 in San Tomas Aquino and Calabazas Creeks watersheds. Over 602 of these manholes, or roughly 4 percent of the modeled system would have more than 12 inch of maximum flood depth. The preliminary model results of the existing system at the 10-year design storm event are shown in Figure 3. 18

19 <V' f i / 91 \ *» * v- * -7L ^ > X ^ ^"1 # v3 / v X \ X N ' ' x Hvvv trax V Ir A \ v V v\ TNH-r. \ / V\ \ \ yi \) XA y* X ) Mi -Xx \ - -" 'XvAvv yv ;// <x > / 1 S x / 1/ v^p 1 \ - ^.., -\ - -V r *** N$\ "&K - xx ' i X\< V >,/v>, < k/'" / /\ v< K\ \ ^w.ai,\'\ u X v \ \ 2V* ^ w X, /f >...,y^t ^ XI Wv ^»- r -»S i *TJ"J t 1 Si /, I t i ^ _,r/ w F^g!..!.i ""?, <vh* i VV'c-: i i_ * U '. -I'rwJ : r4f «1 X ^'sa -/sj?t ' -+*- ** - S 2 -' \X > > J %r~s" CBtE^X - J 3yr24hr Design Storm Event Flood Depth at Surface I > ^ ^-^2 I < 6". Creeks n f v H-i \: ir,^v I /;.^ ' %'^riy%xxx\ _ (jc ^jwtt A.J r" ftvvp?* 1 r X, ***T'?<AVA.,< J, 1,f -. * "* A. er > l t* n.. 'i X X f c /"%\ n " X f>y * v ^ h ^V I vx.i Surcharged Pipes Bottleneck Pipes Modeled Pipes i City Service Area r\ '-. \ ijll 1%, i "\! 1W f xk / 1 J J il.. N NA r V\_ 1 - v \ - v % Figure 2: Preliminary Model Results of Existing System at the 3-year Design Storm Event \ \ V T > J.*, z 1 19

20 L-".** 1 %. T T- A, y XV7 "8. f \Z f v, / I t; s y y'.jz cf^ i. Y?%x vvii'i- \ \ '--.VVv C z-v/ V.VvV v,?v\ V\}<k* 1iVXA A 'V^T N r ^/Kh A50'Jf < h.-> \v\ * \ \ >» * \V, /{, M? r.^^x yyyt. v YffT ' Z XV ; J ;-"-^^g'v\x ^ \ " ***!%. 3 y k W- % )\X/^ d v T-r r * vt, v " OCa n 4- V t, Tfm jb,3ji \ J J Ji$y y\yst\v^s <\ -/>'! ),«r; ffhk iv * V" if L-t.l 11 i J». i tj ' 5" w [ r' r, "*,.' ^ ' w 4 X' J :" i L.i^7 ^jrx ~ ' i J - I lood Depth at Surface "] > 12" 6-12" < 6" <n. X_. -, *«; & ' V> ivtbsbee" CPEi^ % - r \% - '- ffl I \-^L ''Vnx, - V rv^v-v~1 ^--JXiXK x. / Yx,1._, ( \ J» * ' \ "* Ct* 1 >--" x ' s a. '' -t J l'"-i -s X "V» c «Wt7 kf\i <Vi - "s^4 v \\ j-j' -»/ *^4:; t XT a> t *^>t" I Vj» Ld?i «1. V" fl '.5 \ v! ifr r At I Vy L^- J v f r : j "_r. I M - [ f/p ^ -rm?.^r- H' ' ^ "T J ; \"VXX S ^ ' \ r J «i f i, " > : / t ^ V > Surcharged Pipes Bottleneck Pipes Modeled Pipes Creeks j City Service Area t*»v, n%.. a-^otth, - i v7- \. ^ < v, * 7 N %.17 1 J / "'A > '^\'^S.JL 1 lax f. /K / v X "f o»n ' T t \4 / X 1 5 ^ X. L "f: IJS / t;v. JJ.A, f ' \ \v i %X V. % * \ \ \A_ Figure 3: Preliminary Model Results of Existing System at the 10-year Design Storm Event 20

21 The results indicated that about 31 percent of modeled pipes would be deficient at existing system flow. Roughly 41 percent would become deficient if the system could be without bottlenecks. In other word, about 60 percent of the system has the full-pipe capacity for the 10-year design storm event. Compared to the merely 33 percent of the pipes constructed at the 10-year standard, the existing system has performed far better than expected. This may be attributed to the general use of Rational Method and conservative values of percent of impervious area. The proper use of Rational Method should be to predict design peak flow rates from small urban watershed up to 50 acres. The Rational Method is a rather conservative method when compared with the unit hydrograph methods which are used in computer models. Preliminary High Priority Capacity Improvement Locations For the master plan study, the performance criteria is set to maintain the hydraulic grade line (HGL) in the system below the ground surface for the 10-year 24-hour design storm event. A total of 56 areas were identified city wide where the HGL was above the ground surface causing flooding. For this reporting period, staff focused on the areas with flooding on surface exceeding 6 inches during a 3-year storm event. New upgraded pipe sizes for the deficient system were identified to the predicted improve the flooding condition. This was the first step of looking into potential solutions to providing flood protection in high level flooding areas. The preliminary high priority CIP projects were size to maintain the HGL at pipe crown if feasible for the 10-year 24-hour design event, and up to creek levels if the creek level was affecting the upstream HGL. Figure 4 illustrates the locations of the preliminary high priority projects, which upsizing existing storm drains and outfalls, and pump station improvements. Five locations were identified with improved or new pump stations, including Alviso, Charcot, Snell, Santa Teresa and Bluefield pump stations. Table A presents the preliminary planning-level cost estimates for these high priority projects. TABLE A: PRELIMINARY HIGH PRIORITY CIP TO ADDRESS MAJOR CITYWIDE FLOODING LENGTH COUNT OF COUNT OF COUNT TOTAL PROJECT COST OF PIPES MANHOLES OUTFALLS OF PUMP (2016 Million$) UPSIZED REPLACED STATIONS (MILES) GUADALUPE $98.0 COYOTE $30.0 OTHER $8.0 TOTAL $136.0 During the next reporting period, staff will refine projects to address the remaining high level flooding areas, as well as refine projects to alleviate areas with flooding of less than 6 inches. The preliminary cost of an overall capacity improvement program to remove citywide flooding could be over $500 million. 21

22 TTw J S-'~\ A\d>" y* /> Y/J$r \ \.«; / ' j 1 M N\f I. AfSJSkiv -4i "'( 1H j < I^-f n n y #. ; N v ;0 r rjj 1 >..i-u-.j \yl " y w P--. ' /,! I.J3 i rs r ^ J Tzar a v.v'w r S sw X>/., '#.- y )"^T V& / it\ km LA L X * V/VN - 4Qy ' l_! High Priority CIP Pump Stations High Priority CIP Pipes Existing Pipes Creeks City Service Area rvi-fw^vi \\ s"~^ ^J ' ''djv 'X, H T^N. y A -j.4 '--^-i, '1 /^\ & ~xf+ ' :-.'~' -'-v i *>J] 11V \jl Nf> / ' >'. ' 1 ' FX, f>x Y' -.^I r fvo,, < > < p. s - ' W'vr^o! * -V? Y#^. : *f\ / \ \ Hr * i\ *v% / «. \ It/xS > X.c-\ i I- "J" IS-.* * 1 i Vv.^ * 4>A, v V V V A Sounds: Esri. HERE, DeLome^rrtifmap. increment RCffp,, GEBCO. U3GS, FAO, NPS, NRCAN, GsoBase. IGN, Kaclpster NL, Onjnance Survey Esri Japan, M.E.TI, Esr; China [Hcng Kcng), sw?sstapo>mapmylndia, OpenStreetMap contributor^* ^ and tine GIS User Community Figure 4: Preliminary High Priority Capacity Improvement Locations 22

23 Next Steps The model results presented in this report were for existing land use scenario. The master plan study will review the system performance under near-term and long-term General Plan 2040 land use scenarios. In addition to the pipe upsizing alternative initially reviewed, staff will perform alternative analysis to identify cost-effective solutions and optimize the capacity improvement projects with potential inline or offline storage. Suitable green infrastructure projects will be evaluated and considered in the capacity improvement projects to provide water quality benefit. Regional facilities to provide retention or detention of storm water flows will be identified and evaluated as alternatives to the conveyance projects. Preliminary high priority projects' scopes and cost estimates will be refined and will cover other high level flooding areas during the 10-year storm events. Projects to relieve remaining flooding areas will be identified and their costs estimated. The draft report will be prepared for the master plan study with prioritized CIP projects. 2. Support Economic Development Working with Development Services Division, the Master Plan staff reviewed the storm drain capacity for development projects. Because the storm drain model is still under development, the review was done by evaluating the existing capacity against the runoff calculated using the Rational Method in Excel spreadsheets. The partial list of development projects that staff conducted capacity reviews included Santa Clara BRT, Agnews, Communications Hill, Cannery Park, Santana West, and West Julian developments. 3. Coordination with Santa Clara Valley Water District (District) Approximately 20 percent (or 250) of the storm outfalls are in need of rehabilitation in order to maximize operational capacity and minimize maintenance requirements. The range of improvements needed include flap gate repair, vegetation removal, sediment removal, riprap repair, bank erosion repair, channel dredging, and/or outfall structure and pipe reconstruction. The City does not have a comprehensive outfall program to address the widespread planning and funding needs, environmental and regulatory permitting requirements, and mitigation and monitoring plans that would be necessary to implement a robust and long-term program. Currently, repairs to existing outfalls are considered on a case-by-case basis; when possible the City has been collaborating with the District to implement select projects through their Stream Maintenance Program or Five-Year Capital Improvement Program. This approach will continue to be used to rehabilitate outfalls in conjunction with ongoing District river and creek channel improvement projects (Coyote Creek, Guadalupe River, Los Gatos Creek, Lower Silver Creek, Thompson Creek, etc.) Storm Sewer System Annual Report FY

24 City staff has closely coordinated with the District on the progress of the City's storm master plan development. Staff provided results of the North San Jose and Alviso area storm drain master plan study to the District. Potentially, the City would like to partner with the District to improve the storm sewer system in those areas to 10-year and 100-year storm event standards. The Water District has requested the City to assist them in their flood protection studies of Lower Silver Creek, Ross Creek, Upper Penitencia Creek, and Canoas Creek by making these areas' modeling the highest priorities of the City's modeling project. 4. Neighborhood/Special Corridors The citywide master planning effort is expected to yield the data necessary to plan and estimate Storm Capital Projects. Currently, most storm system improvement projects are identified and selected for implementation based on public complaints and City staff observation, as well as historical knowledge of chronic/re-occurring drainage problems. These improvement projects are funded by the Storm Sewer Capital Improvement Program (CIP). Priority for funding of storm improvement projects through Neighborhood/Special Corridors funding is based on proximity to public gathering centers, such as schools, community centers, libraries, etc. 5. Rehabilitation of Pump Stations As noted above, the City owns and operates 30 storm pump stations with various capacities. The majority of the City's 30 pump stations are over 40 years old. Although the majority of the storm pump stations have been rehabilitated within the last 20 years, Public Works continues coordination with the Department of Transportation to develop and implement a plan for prioritizing the rehabilitation of the City's storm pump stations. 6. Improving Annexation Areas In April 2006, the San Jose City Council launched a three to five year program in which the City of San Jose will annex the remaining "islands" (or "pockets") of less than 150 acres of unincorporated County of Santa Clara land. Unincorporated islands are governed by and receive services from the County even though they are completely or substantially surrounded by incorporated, or City lands. Upon annexation, the land use and general governing responsibility changes from the County of Santa Clara to the City of San Jose. This change enables residents in these County islands to receive urban services from the City rather than the County. The addition of these pockets to the City service area increases the demand on existing City storm infrastructure. The total impact of the annexation to the storm program is unknown, but County pockets typically lack underground storm sewer pipes and tend to experience various problems related to ponding. In addition the lack of curbs and gutters does not address the current standards for protection from overland release (streets are designed to capture the effects of the 100-year storm or failure of the storm sewer system). The city-wide master planning effort is expected to identify any deficiencies or needs for improvements within the recently annexed County pockets. 24