Town of San Anselmo Flood Advisory Committee  MEETING MINUTES PROJECT: DATE: SUBJECT: ATTENDEES:  Town of San Anselmo Flood Committee Meeting February 8, 2010 Flood Committee Meeting  Name Tom Mclnerney Ford Greene Glenn Dearth Reinhard Ludke Richard Stutsman  Discussion  Brief:  2. Elect Chair & Vice Chair  Committee Chair Tom McInerney Committee Vice Chair Dick Stutsman  MSC 5-0  3. Steve Myrter presented powerpoint overview of County Ross Valley watershed flood risk reduction study performed by Stetson Engineers as managed by Jack Curley, County Engineer - County Flood  Control Zone 9. see ntplwww.rossvaleywatershed.org  4. Update on Town storm planning and preparation. Town Hall flood protection construction is complete. Ross Valley Fire Station 19 remodel construction is complete. Planning study at San Anselmo Avenue is considering storm water detention basin. Small local detention basins are encouraged to reduce  storm runoff.  5. Dick Stutsman presented October 13, 2009 and January 18 - 19, 2010 Stream Gage Storm Data.  Record data is attached.  6. Chris Martin, Town of Ross, reported on Army Corps progress on Ross Unit 4. The Corps has made: limited progress due to changes in personnel and limited funding. He provided a Town of Ross Draft  copy- STORMWATER MANAGEMENT ORDINANCE  attached  Reinhard Ludke Secretary  Meeting Minutes 100208  Page 1    Town of San Anselmo Flood Advisory Committee  7. Discussion of flood gates on commercial buildings in downtown. 40% to 50% of merchants/property owners have installed flood gates. There was discussion about mandating flood gates by ordinance. There was discussion that flood gates may reduce flood risk but do not prevent water damage when water levels are higher than floor levels, timber buildings are not watertight. Flood gates will be.  considered int future meetings of the committee.  8. Discussion ofi interim flood protection measures were discussed with suggestions from the public which  include:  Rain catchment and storage - cisterns  Bioswales Biologic drain inlets Permeable paving Rain gardens  The committee suggested that other flood prevention experts and lessons from City of Napa and Napa  River flood prevention may be consulted.  9. Town will solicit resumes and consider adding two new flood committee members.  10. Public Expression  11. Next meeting March 8, 2010  ACTION ITEMS  Evaluate interim flood risk reduction measures  Town Regulation mandate requirement for owners to mitigate flood damage by ordinance and/ or  mandate flood gate installation?  Schedule presentation of County Study progress report- - Fall 2010  Meeting notes corrections and additions should be directed to the author or Debbie Stutsman  CC:  Attendees  Jack Curley, Debbie Stutsman Town Manager, Steve Myrter Public Works Director  Reinhard Ludke  Minutes 100208  Secretary  Meeting  Page: 2    (uyrui) OL x aes lejuies (sayour) mejuies eApeunsoy  00 0    Wd 00:6 Wd00:8 Wdoo:Z Wd00:9 Wdo 00:9 do0:t Wdooc Wdooz Wdoo:l Wdo0zr WVOOLL WVOO:OL WV00:6 WV00:8 WVOO:L WV00:9 WV 00:9 WV 004 WV 00:E WVOOZ WVOO:L WV 00:ZL  -  5  2  5  (jeay): 14610H aoejns1egeM    (ayru) OL xajes Iejuies (seyouI) mejuies eApejnunsoy 6 5 4  o  3 2  WVOO:LL WVOO:OL WV00:6 WV00:8 WVOO:L WV00:9 WVOOS WVO 00:4 IV 00F IV 00:2 WVOO:L WV 00:21 Wd 00:LL Wd 00:0L Wd 00:6 Wd 00:8 Wd 00:L Wd 00:9 Wd 00:9 Wd 004 Wd 00:E Wd 00:2 Wd 00:L Wd 00:2L WV 00:LL WVOO:OL WV00:6 WV00:8 WVOO:L WV00:9 WVO0:9 WV00V IV 00:E WV 00:2 WVO 00: WVO0ZL  S  6o 5  2  (jaay) 34610H esepng.egeM    (ayrui) OL x ejey legules (seyour) Iejuies eApejnunsoy  Co  6 5 4 3 2  WV 00:2L Wd 00:LL Wd 00:0L Wd 00:6 do 00:8 Wdoo:Z Wdo09 Wdoo:g Wd 004 Wdoos Wdo 00:2 Wd 00:L Wd 00:ZL WVOO:LL WVOO:OL WV00:6 WV00:8 WVOO:L WV00:9 WVOO:9 WVOOt WVOO:E WV0OZ WVOO:L WVOOZL  @  S  E e 0 6 R 00 10 28 00 a De -  (jaay) 14610H epejng.egem    EVALUATION OF RUNOFF DUE TO SOIL SATURATION  October 13th, 2009 Storm: (4:45 hour period)  0300 Stage = 2.24 feet Rain =0.01 inches 0745 Stage= 4.77feet Rain 2.26inches  Maximum Rain Intensity: 0.8 inches/hour Reduction: 2.53 feet/2.25inches: = 1.12 feet /inch  January 18Hh, 2010Storm: (5hour period)  0700 Stage = 3.48 feet Rain =0.25 inches 1200 Stage = 6.72feet Rain = 1.26inches  Maximum Rain Intensity: 0.76inches/hour Reduction: 3.24 feet/1.01 inches = 3.21 feet/inch  January 19th, 2010 Storm: 4:15hour period)  0300 Stage = 3.50feet Rain =1.33 inches 0715 Stage = 7.55 feet Rain = 2.79 inches  Maximum Rain Intensity: 0.88 inches/hour Reduction: 4.05 fee/1.46inches-2 2.77 feet/inch  January 20th,2 2010Storm: (5:45 hour period)  0330 Stage = 4.03f feet Rain =3.84 inches 0915 Stage = 9.95 feet Rain = 5.17inches  Maximum Rain Intensity: 0.60inches/hour Reduction:5.92reu3 inches = 4.45feet/inch  January 20,2010 Storm:  0330 Stage =4 4.03 feet Rain =3.84 inches 0915 Stage-9.95feet Rain = 5.17inches  Maximum Rain Intensity: 0.60inches/hour Reduction: 5.92 feet/1.33 inches = 4.45 feet/inch    Desisys Reus Zangn  Draft, 10/29/09 Town of Ross  7 lool  i  STORMWATER MANAGEMENT ORDINANCE  SECTION 1. TITLE.  This ordinance shall be known as the "Stormwater Management Ordinance".  SECTION 2. PURPOSE The purpose ofthis ordinance is:  (A) To better manage land development in order to protect, maintain, and enhance the public heath, safety, and general welfare of the citizens of the Town of Ross by establishing minimum requirements (B) To promote stormwater management practices that maintain pre-development hydrology through site design, site development, building design and landscape design techniques that infiltrate, filter, (C)To protect natural resources, particularly creeks, wetlands, floodplains, San Francisco Bay, and other natural aquatic systems on the development site and elsewhere from degradation that could be caused by (D) To protect other properties from damage that could be caused by stormwater and sediment during (E) To reduce the impacts from impervious surfaces such as streets, parking lots, rooftops and other  and procedures to control the adverse impacts associated with stormwater runoff,  store, evaporate and detain stormwater close to its source;  construction activities and post-construction conditions;  construction activities and post-construction conditions on the development site;  paved surfaces;  (F)Tor minimize prolonged business and traffic interruptions; and  (G) To protect public safety from flooding and streambank erosion, reduce public expenditures in removing sediment from stormwater drainage systems and natural resource areas, and to minimize  damage to public and private facilities.  SECTION3. SCOPE AND APPLICABILITY  (A) This ordinance shall apply to all development within the Town of Ross requiring a permit for  construction. (B)E Exemptions:    (1)Any activity that will disturb an areal less than five hundred (500) square feet;  (2) Any activity that will increase an impervious area or contiguous impervious area less than (3)The construction of any fence that will not alter existing terrain or drainage patterns.  two hundred fifty (250) square feet;  SECTION 4. STORMWATER MANAGEMENT APPLICATION MATERIALS or plans drawn to scale with supporting documents and technical details as necessary:  For all development requiring a building permit, the following information shall be presented on a plan (A). An existing condition site assessment providing baseline information on features relevant to erosion and stormwater control including site boundaries, existing building and impervious area footprints, topographic contours, tree canopy driplines, percent slope labeled slope direction arrows, cross-section profiles showing representative site gradients, soil types, vegetation type, natural and human-made or altered waterbodies within or directly adjacent to the site including streams, watercourses, human-made oraltered drainage ways, landscape drainage pipe networks, culverts, floodplains, wetlands and sensitive natural communities, and site features that aid in stormwater management including natural and forested and vegetated lands located on stream and wetland buffers and other areas that are known or believed to be subject to temporary ponding of stormwater. The existing conditions site assessment shall show the dimensions of individual facilities and all junction invert elevations comprising the existing stormwater drainage facilities within or directly adjacent to the site. The existing conditions site assessment shall show all areas of land outside of the site boundaries but within the Town of Ross comprising the drainage areas tributary to any and all streams, watercourses, human-made or altered drainage ways, and (B). An erosion prevention and sediment control plan identifying the expected construction disturbance area that shows the amounts, locations, arrangements, and types of temporary erosion control measures (e.g., silt fences, seeding and mulching, temporary grades, sediment basins, sediment pump and filter systems, excavation phasing to minimize disturbance during the rainy season, etc.) that will be implemented at the site to prevent erosion during construction to prevent sediment runoff from the site both during construction and during the immediate post-construction period, including measures or facilities designed specifically for handling rainfall-runoff amounts to be expected during rainy season (C) A stormwater control plan identifying and tabulating the existing and proposed construction disturbance area and impervious surface areas and demonstrating that peak stormwater. runoff from the 3 site is maintained at pre-development levels or otherwise minimized as far as practically feasible through the use of natural drainage systems and on-site infiltration and treatment techniques. The plan shall demonstrate that soils best suited for infiltration are retained and that natural areas consisting of tree canopy and other vegetation are preserved, preferably in contiguous blocks or linear corridors where feasible, for protection ofthe best stormwater management features identified ini the site assessment. The Planning Director and or the Town Manager may consider and impose appropriate safeguards, modifications and conditions relative to the general standards and guidelines listed in Section 7 of this  culverts passing onto and through or running directly adjacent to the site.  conditions, ifapplicable.  ordinance.  SECTION: 5. GENERAL PRE-DEVELOPMENT AND CONSTRUCTION SITE STANDARDS.  2    All development in the Town of Ross is subject to the following pre-development and construction site standards to ensure that all sources of soil erosion and sediment on the construction site are adequately controlled, and that existing site features that naturally aid in stormwater management are protected to (A) Minimize Land Disturbance. Development of a lot or site shall require the least amount of vegetation clearing, soil disturbance, duration of exposure, soil compaction and topography changes as  the maximum extent practical.  possible.  (1) To the extent feasible, soils best suited for infiltration shall be retained and natural areas. consisting of tree canopy and other vegetation shall be preserved, preferably in contiguous (2) The time the soil is left disturbed shall be minimized. The Planning Director and or Town Manager may require project phasing to minimize the extent of soil disturbance and erosion (3) There shall be no soil compaction except in the construction disturbance area, which shall be identified and delineated in the field with appropriate safety or landscape fencing. In areas outside the disturbance area there shall also be no storage of construction vehicles, construction (4) Development on steep slopes equal to or in excess of 15%, or which results in such slopes,  blocks or linear corridors.  during each phase ofs site development.  materials, or fill, nor shall these areas be used for circulation.  shall be subject to conditional use review.  (B) Preserve Natural Areas. Development shall not result in an undue adverse impact on fragile environments, including wetlands, wildlife habitats, streams, lakes, steep slopes, floodplains and  vegetated riparian buffers.  (1) Open space or natural resource protection areas shall be retained preferably in contiguous blocks or linear corridors where feasible, for the protection of the best stormwater management features identified in the site assessment as required in Section 4(A)ofthis ordinance. (2) Forested lands located on stream and wetland buffers and steep slopes are priority areas and clearing them shall be avoided in order to protect wildlife habitats and prevent erosion and sedimentation resulting from stormwater runoff. Exceptions to this standard may be appropriate for clearing of primarily non-native vegetation and replacement with native California riparian woodland trees, shrubs, and understory vegetation within exiting stream and wetland buffers, or floodplain restoration projects requiring tree removal and excavation to achieve active floodplain : (3)Ar minimum 25-foot from top-of-bank vegetated buffer shall be established along any streams (4) Lot coverage and building footprints shall be minimized where feasible, and development clustered, to minimize site disturbance area and preserve large areas of undisturbed space. Environmentally sensitive areas, such as areas along streams, forested areas, and steep slopes  elevations and appropriate floodplain vegetation. where the buffer: is located within the property lines.  shall be aj priority for preservation and open space.  3    (C) Manage Water, Prevent Erosion and Control Sediment During Construction. Applicants shall maintain compliance with the accepted erosion prevention and sediment control plan as required by  Section 4(B) ofthis ordinance.  (1) Runoff from above the disturbance area and construction site must be intercepted and (2) On the site itself, water must be controlled, and kept at low velocities, to reduce erosion in (3) The amount of sediment produced from areas of disturbed soils shall be minimized by implementing control measures such as scheduling and timing of grading activities, vegetated strips, diversion dikes and swales, properly sized sediment traps and basins, check dams, installation of construction entrances to prevent tracking of sediment onto adjacent streets, dust control, pump and filter systems, to reduce entry of suspended sediment into storm drain system and watercourses, and silt fences. Pollution prevention practices may include designated washout areas or facilities, control oft trash and recycled materials, tarping of materials stored on- site, and proper location of and maintenance of worker sanitary facilities. The combination of BMP's used, and their execution in the field, must be customized to the site using up-to-date (4) Immediate seeding and mulching or the application of sod shall be completed at the conclusion ofeach phase of construction, or at the conclusion ofc construction ifnot phased. (5) The applicant shall follow the erosion prevention and sediment control practices for  directed around the disturbed area during site disturbance and construction.  drainage channels.  standards and practices.  construction that occurs during the rainy season from October 151 to April 15.  SECTION 6. LOW IMPACT DEVELOPMENT DESIGN  The use of LID design approaches is preferred and shall be implemented to the maximum extent practical given the site's soil characteristics, slope, and other relevant factors. To the extent that LID design approaches are not proposed in the stormwater management plan [isi it stormwater control plan or stormwater management plan?), as required in Section 4(C) oft this ordinance, the applicant shall provide a full justification and demonstrate why the use ofLID approaches is not possible before proposing to use conventional structural stormwater management measures which channel stormwater away from the  development site.  SECTION 7. LID/S STORMWATER GENERAL POST CONSTRUCTION REVIEW  STANDARDS AND GUIDELINES  All applications for development are subject to the following post construction stormwater management standards and guidelines to ensure that stormwater management approaches that maintain natural drainage patterns and infiltrate precipitation are utilized to the maximum extent practical. Standards are statements that express the development and design intentions of this ordinance. The guidelines suggest a variety of means by which the applicant might comply with the standards. The guidelines are intended to aid the applicant in the design process and the Planning Director and or Town Manager when reviewing applications. Options for compliance with the standards are not limited to the  guidelines listed.  4    Standard 1: Vegetation and Landscaping  Vegetative and landscaping controls that intercept the path of surface runoff shall be considered as a  component oft the comprehensive stormwater management plan.  Guideline 1.1. Utilize two-track surfaces with grass in-between to provide water infiltration for Guideline 1.2. Design parking lot landscaping to function as part of the development's stormwater management system utilizing vegetated islands with bioretention functions. Guideline 1.3. Incorporate existing natural drainage ways and vegetated channels, rather than the standard concrete curb and gutter configuration to decrease flow velocity and allow for Guideline 1.4. Divert water from roof downspouts away from off-site stormwater pipe networks, the street, driveway and parking lot surfaces and into bioretention areas or rain gardens to Guideline 1.5. Encourage construction of vegetative LID stormwater controls (bioretention, Discourage construction of subsurface landscape drainage pipe networks for lawn drainage. Such systems should discharge into detention and infiltration areas on-site rather than off-site  roads, driveways, parking lots and other types ofdrivable or walkable surfaces.  stormwater infiltration.  capture, store, and infiltrate stormwater on-site. swales, filter strips, buffers) on land held in common.  stormwater pipe networks, the street, driveway and parking lot surfaces.  Standard 2: Development on Steep Slopes  Development on steep slopes equal to or in excess of 15% shall be sited and constructed, and slopes stabilized to minimize risks to surface and ground waters and to protect neighboring properties from  damage.  Guideline 2.1. Discourage development, re-grading and clearing of vegetation on land where the Guideline 2.2. Locate house sites, subsurface sewage systems and parking areas on the flattest Guideline 2.3. Minimize crossing steep slopes with roads and driveways and lay them out to follow topographic contours in order to minimize soil and vegetation disturbance. Avoid long :  slope is greater than 35%. portion oft the site.  driveways.  Standard 3: Reduce. Impervious Surfaces  Stormwater shall be managed through land development strategies that emphasize the reduction of impervious surface areas such as streets, sidewalks, driveway and parking areas and roofs.  Guideline 3.1. Evaluate the minimum widths ofall streets and driveways to demonstrate that the proposed width is the narrowest possible necessary to conform with safety and traffic concerns Guideline 3.2. Reduce the total length of residential streets by examining alternative street layouts to determine the best option for increasing the number of! homes per unit length.  and requirements.  5    Guideline 3.3. Minimize the number of residential street cul-de-sacs and incorporate vegetated islands to reduce their impervious cover. The radius of cul-de-sacs should be the minimum required to accommodate emergency and maintenance vehicles. Consider alternative turn-around Guideline 3.4. Reduce driveway lengths by minimizing setback distances. Ençourage common Guideline 3.5. Use permeable pavement for parking stalls and spillover parking, sidewalks, Guideline 3.6. Establish parking maximums and utilize shared parking for uses with different  areas. driveways.  driveways and biket trails. peak demand periods.  Guideline 3.7. Reduce building footprints by using more than one floor level.  Standard 4: Low Impact Integrated Management Practices (IMPs)  Stormwater shall be managed through the use of small-scale controls to capture, store and infiltrate  stormwater close to its source.  Guideline 4.1. Preserve and/or create vegetated depressions, commonly known as biorention areas or rain gardens that collect runoff and allow for short-term ponding and slow infiltration. Rain gardens consist of an approx. six inch or more depressed or bowl shaped planting bed that iss sized to treat runoff from storms ofapprox. one inch depth. Amended soils and drain rock and perforated pipe subsurface drainage are often installed at depths upi to 2.5 ft below the depression to achieve the target infiltration performance. Design for controlled discharge of excess runoff from bioretention areas via overland sheet flow or via channeled vegetated swales where Guideline 4.2. Locate above-ground or subsurface cisterns or subsurface dry wells consisting of Guideline 4.3. Use filter strips or bands of dense vegetation planted immediately downstream of ar runoff source to filter runoff before it enters a receiving structure or water body. Natural or man-made vegetated riparian buffers adjacent to waterbodies provide erosion control, sediment Guideline 4.4. Utilize shallow grass-lined channels or "vegetated swales" or 6E bioswales". to Guideline 4.5. Incorporate rooftop gardens or "green roofs" which partially or completely cover aroofwith vegetation and soil or a growing medium, planted overa waterproofing membrane. Guideline 4.6. Use permeable paving and sidewalk construction materials that allow stormwater tos seep through into the ground, including providing for appropriate subsurface conditions and Guideline 4.7. Use rain barrels and cisterns of various sizes that store runoff conveyed through building downspouts. Rain barrels are generally smaller structures, located above ground. Cisterns are larger, often buried underground, and may be connected to the building's plumbing  practically feasible.  gravel or stone-filled pits to catch water from roofdownspouts or paved areas.  filtering and habitat.  convey and store runoff.  future maintenance for infiltration performance as designed.  6    or irrigation system. Manually or automatically empty rain barrels after individual storms during Guideline 4.8. Add minerals and organic materials to soils to increase its capacity for absorbing Guideline 4.9. Utilize tree box filters placed below grade, covered with a grate, filled with filter media and planted with a tree, to act both as a water retention tank and a natural filter.  the winter rainy season (October 15 to April 15). moisture and sustaining vegetation.  SECTION: 8. INDEPENDENT CONSULTANTS.  The Planning Director and or Town Manager may retain independent consultants to facilitate the review of applications for development subject this ordinance and whose services shall be paid for by the applicant. The consultant(s) shall work at the Planning Director's direction and shall provide the Planning Director such reports and assistance, as the Planning Director deems necessary to determine  compliance with this ordinance. SECTION: 9. OTHER LAWS. laws ofthe State ofCalifornia. SECTION 10. SEVERABILITY.  This ordinance is in addition to all other ordinances and bylaws of the Town of Ross and all applicable  If any section of this ordinance is held by a court of competent jurisdiction to be invalid, such finding  shall not invalidate any other part oft this ordinance.  7    Resolution  WHEREAS, Marin County's Ross Valley has a long history of flooding, which threatens human life and has caused severe damage to the residential, commercial, and institutional properties along the Corte WHEREAS, in 1962, the U.S. Congress recognized this problem and enacted the Flood Control Act of 1962 to direct the U.S. Army Corps of Engineers toj provide flood prevention improvements. along a 6.5 mile stretch ofCorte Madera Creek from San Francisco Bay through the towns ofCorte Madera, Larkspur, Kentfield, Ross, San Anselmo to Fairfax (referred to as Units 1-6); and WHEREAS, in 1971, after the completion ofUnits 1,2, and 3, the cities ofl Fairfax and San Anselmo (Units 5 and 6) opted out oft the project, the Water Resources Development Act of1986 limited the scope of the. Army Corps ofEngineer's project through Unit 4, which extends from the upstream end of the existing concrete channel to the Sir Francis Drake Boulevard Bridge at the upstream boundary oft the WHEREAS, significant components of the. Army Corps ofl Engineer's project include: (1)a natural sediment basin within the existing channel, (2) raising oft the floodwalls in Units 2 and 3, (3)removal and replacement oft the fish ladder in Unit 4, and (4) bank stabilization work along the Unit 4; and WHEREAS, the project will reduce the flooding risk, as well as fully respect the environmental concerns expressed by the community, including minimizing the use of concrete, maintaining a way for WHEREAS, for several years, the Army Corps of] Engineers has been conducting required environmental review for the project, including aj joint Environmental Impact StatemenvErnvronmenta WHEREAS, this process is taking longer to complete than originally represented and senior staff WHEREAS, there is no certain date for the actual completion of this project, which was originally WHEREAS, the Army Corps ofEngineers' Unit 4 project is a critical component oft the Ross Valley WHEREAS, the Army Corps ofl Engineer's hydrologic and engineering studies, and the actual project improvements are vital part ofthe collaborative federal, state, county, and municipal effort to reduce the NOW,THEREFORE, BE: IT RESOLVED, that the Town ofRoss urges the U.S. Army Corps of Engineers and our elected officials to expedite the implementation and completion oft the project work related to Unit 4. This project is long overdue and is a vital link to reducing the risk of flooding in Ross  Madera Creek; and  Town of Ross and the Town of San Anselmo; and  fish to pass, and preserving plants and trees; and  Impact Report (EIS/EIR); and  previously working on this project have been reassigned to other projects; and  assigned by the U.S. Congress forty-seven years ago; and Watershed Flood Protection Program for Corte Madera Creek;  flooding of the Corte Madera Creek.;  Valley.