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Strengthen, Preserve and Enhance the Unique Identity of the City's CHAPTER 6 Safety and Noise This chapter has two sections: Safety and • Calaveras Fault, northern segment: 11 Noise. percent SAFETY • Concord Fault: 4 percent • Mt. Diablo Thrust Fault: 3 percent Every general plan in California must have a • Greenville Fault: 3 percent “safety element” that addresses natural and manmade hazards and dangers. This section of General Plan 2025 examines and aims to reduce See Figure 1, Regional Faults and Probabilities, the potential risk of death, injuries, property page 6-2, and Figure 2, Area Faults, page 6-3. damage, and economic and social dislocation The City’s objectives are to prevent geologic resulting from fires, floods, earthquakes, land- hazards in new projects and reduce the risk of slides, and other hazards. these hazards in existing developed areas. This section is presented in seven parts: • Seismic and Other Geologic Hazards GOAL 1 • Flooding Protect life and property • Hazardous Materials from geologic hazards. • Fire Hazards • Public Safety Policy 1.1. Reduce the potential effects of • Disaster Response seismic and other geologic hazards, including slope insta- • Water Supply bility. SEISMIC AND OTHER Action 1.1.1. Identify areas prone to seismic and other geologic hazards, in- GEOLOGIC HAZARDS cluding slope instability. The United States Geological Survey (USGS) has established probability estimates for sig- Action 1.1.2. Establish minimum road widths nificant earthquakes (magnitude 6.7 or greater) and clearances around struc- between 2003 and 2032. The following prob- tures at risk from known geo- abilities are estimated for faults in and around logic hazards. Walnut Creek: Action 1.1.3. Review and update the existing • Hayward/Rodgers Creek Fault: 27 maps of geologic hazards. percent April 4, 2006 Walnut Creek General Plan 2025 6-1 Chapter 6, Safety and Noise CONCORD/ GREEN VALLEY FAULT RODGERS Vacaville Sonoma Napa CREEK Fairfield FAULT Vallejo 4% SAN 27% Martinez Concord San Rafael Richmond Walnut Creek Planning Area Berkeley Pacific THRUST MT.DIABL FAULT GREENVILLE Ocean ANDREAS Oakland HAY O San Francisco WARD 3% 3% Hayward F San A FAULT Pleasanton SAN Francisco ULT Bay 11% Fremont 21% CALA VER GRE Redwood F City AULT AS GORIO Palo Milpitas Alto San Jose FAULT 10% Legend ProbabilityProbability of 6.7 Richter scale earthquake, 2003 to 2032 10% or more FAULT E 5-9.9% in Lomx te n t o a 1-4.9% P f Rupture rieta Source: USGS Working Group 2002 (2003) Quake 0 5 10 Miles Figure 1. Regional Faults and Probabilities 6-26-3 Walnut Creek General Plan 2025n Chapter 6, Safety and Noise Concord Pleasant Hill d lv T t B AR ea B Tr O a k Lime Ridge G r o Open Space v e R d B a n c Geary Road r o ft R Boundary d d B t R ey Oak u S ll a e V n i o n ci a a a gn M Y V i N s t a Heather A v Farm e r D W alnut 0 c A i v 8 e v 6 i - I C C a s t le R o c k R d BART Hwy 24 Shell Ridge W al Open Space Lafayette nu t B l vd vd Bl c pi ym Ol Rudgear Rd Tic e V alle y B lvd I - 6 8 0 R o s s m o o r P k w y Area Faults Concord Highways Lafayette Major Roads Las Trampas City Limit Mt. Diablo Thrust N. Calaveras Planning Area Boundary Alamo N. Calaveras (extension) South Hampton and Franklin Walker Canyon Alquist-Priolo Earthquake Fault Zone Miles 00.511.520.25 Base Map Data: January 16, 2004 Source: USGS, 1994 Figure 2. Area Faults April 4, 2006 Walnut Creek General Plan 2025 6-3 Chapter 6, Safety and Noise Action 1.1.4. Require appropriate mitigations and property from earthquake- for new development or rede- induced hazards. velopment in areas prone to seismic and other geologic haz- Action 1.2.5. For development proposals ards. submitted in areas near high or very high liquefaction- Policy 1.2. “Limit development within susceptibility areas, require a high-risk geologic areas to a geotechnical evaluation to iden- maximum density of one tify hazard mitigation measures dwelling unit per 20 acres.”1 needed to reduce the risk to life and property from liquefaction- Action 1.2.1. “Identify high risk areas after induced hazards. taking into account soil stabil- ity, history of soil slippage, proximity to earthquake faults, FLOODING slope grade, accessibility, and Historically, several streams in the Planning drainage conditions, and con- Area have flooded, including Walnut Creek, tinue to assign low intensity Las Trampas Creek, Grayson-Murderers uses, not exceeding a density of Creeks (particularly in the Eccleston Avenue one dwelling unit per 20 acres, area), and San Ramon Creek (primarily at the to such areas. Responsibility: confluence of the waterways downtown). City Council.” See Figure 3, Smaller streams subject to flooding include Liquefaction Susceptibility, Tice Creek (particularly in the Castle Hill page 6-5, and Figure 4, Mapped area)—and the Walnut Boulevard channel Landslides and Slopes Greater (also known as Homestead Creek) between than 15 Percent, page 6-6. Homestead Boulevard and Sierra Drive. (See Figure 5, Flood Zones, page 6-8.) Action 1.2.2. As updated seismic-hazard zone maps become available, incorporate them in the general plan. GOAL 2 Action 1.2.3. Identify areas where surface Reduce the potential for ruptures are most likely to oc- flooding in flood-prone cur and cause damage to hu- areas. man-made structures, such as dams. Policy 2.1. Reduce the risk of property Action 1.2.4. For development proposals damage and personal injury submitted in areas near earth- due to flooding. quake fault zones listed under the Alquist-Priolo Act, require a Action 2.1.1. Limit the amount of impervious geotechnical evaluation to iden- surface in flood-prone areas. tify hazard mitigation measures needed to reduce the risk to life Action 2.1.2. Limit runoff in flood-prone ar- eas. 1 Policy 1.2 and Action 1.2.1 address the requirements of Measure P, Ord. 1781, 11/5/91, Sections 3g and 3h. See Appendix B for the complete “Walnut Creek Hill- side/Open Space Protection Ordinance,” Measure P. 6-4 Walnut Creek General Plan 2025 April 4, 2006 Chapter 6, Safety and Noise Concord Pleasant Hill d lv T t B AR ea B Tr O a k G r o v e R B d a Lime Ridge n c Geary Road r Open Space o f t R t d d Boundary B R S y e u ll Oak n a e i o V n a i ac a n M g Y V N i s t a Heather A v Farm e r D Waln 0 c ut i A 8 ve v 6 i - I C C a s t le R Hwy 24 o c k R BART d W al nu t B Lafayette l vd vd Bl c pi ym Ol Shell Ridge Open Space Rudgear Rd Tic e V alle y B lvd I - 6 8 R 0 o s s m o o r P k w y Liquefaction Susceptibility Water bodies Low Highways Medium Alamo Major Roads High City Limit Very High Planning Area Boundary Miles 00.511.520.25 Note: Areas with no color are classified as having "Very Low" liquefaction susceptibility. Base Map Data: January 16, 2004 See text for further explanation of categories. Source: USGS Open File 00-444, 2000 Figure 3. Liquefaction Susceptibility April 4, 2006 Walnut Creek General Plan 2025 6-5 Chapter 6, Safety and Noise Pleasant Hill Concord d lv T t B AR ea B Tr O a k G r o v e R B d a Lime Ridge n c Geary Road r Open Space o f t R t d d Boundary B R S y e u ll Oak n a e i o V n a i ac a n M g Y V N i s t a Heather A v Farm e r D Waln 0 c ut i A 8 ve v 6 i - I C C a s t le R Hwy 24 o c k R BART d W al nu t B Lafayette l vd vd Bl c pi ym Ol Shell Ridge Open Space Rudgear Rd Tic e V alle y B lvd I - 6 8 R 0 o s s m o o r P k w y Percent Slope Landslides 0 - 15% Alamo Highways 15 - 30% Major Roads 30 - 49% City Limit Miles 00.511.520.25 > 49% Planning Area Boundary Base Map Data: January 16, 2004 Source; USGS 1979 Regional Slope Stability Map, 1979; California Division of Mines and Geology, 1995, 1996. Figure 4. Mapped Landslides and Slopes Greater than 15 Percent 6-6 Walnut Creek General Plan 2025 April 4, 2006 Chapter 6, Safety and Noise Action 2.1.3. Work with the County to adopt similar standards for unincor- porated parts of the Planning Area. Action 2.1.4. Collect drainage fees for pro- jects in designated drainage- improvement areas. Action 2.1.5. Work with creekside property owners to reduce and mitigate flood hazards. April 4, 2006 Walnut Creek General Plan 2025 6-7 Chapter 6, Safety and Noise P in e C r Concord e e Pleasant Hill k d T lv AR t B B ea Tr O a k G r o v e R B d a n Lime Ridge c Geary Road r o Open Space ft R d d R Boundary B y t le u al Oak S V e io n n c i a a n a g Y V k M e i s e N r t C a t Heather A u v n Farm l e a r W D W alnut 0 c A i v 8 e v 6 i - I C C a s t le R o c k R Hwy 24 d L it tle P BART in e Cr eek W al nu t B l Lafayette vd vd Bl c pi ym Ol Shell Ridge Open Space Rudgear Rd Tic e V alle y B lvd I - 6 8 R 0 o s s m o o r P k w y 100-Year Flood Zones Natural creek Channel Highways Major Roads City Limit Planning Area Boundary Alamo Miles 00.25 0.5 1 1.5 2 Base Map Data: January 16, 2004 Source: FEMA Flood Insurance Rate Maps,, 1996, 2002 Figure 5.
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