HYDROLOGY & WATER QUALITY

INTRODUCTION

This section evaluates the potential impacts of the project on drainage, flood hazards and water quality. The section was prepared in association with Schaaf & Wheeler, Inc. Schaaf & Wheeler conducted a hydraulic analysis and reviewed the proposed project drainage system as part of the preparation of this EIR. Their technical review memos are included in Appendix E.

ENVIRONMENTAL SETTING

IN THIS SECTION: ƒ Regulatory Setting ƒ Regional Hydrological Setting ƒ Site Stormwater Drainage ƒ Flood Hazards ƒ Water Quality ƒ Groundwater Management

ƒ Regional and Local Plans

REGULATORY SETTING

A number of federal, state, and local laws and plans regulate activities to protect water quality and reduce flood hazard risks. The following sections summarize the principal regulations that pertain to the project site.

Federal Regulations

CLEAN WATER ACT

The Clean Water Act (CWA) regulates the discharge of pollutants to waters of the United States from any point source, enacted in 1972. Section 401 of the CWA requires water quality certification for any activity, including the construction or operation of a facility, which may result in any discharge into navigable waters (Title 33 CFR §1341). Section 404 of the CWA requires a permit for the discharge of dredged or fill material into navigable waters at specified disposal sites (Title 33 CFR §1344). In 1987, amendments to the CWA added Section 402(p), which establishes a framework for regulating non‐point source storm water discharges

TOWN OF LOS GATOS DRAFT EIR L INDA C OURT R ESIDENCES 4.3-1 JANUARY 2010 HYDROLOGY & WATER QUALITY

under the National Pollutant Discharge Elimination System (NPDES). The NPDES storm water program is further described below under the “State Regulations” subsection.

FEMA FLOOD MANAGEMENT

The Federal Emergency Management Agency (FEMA) – a former independent agency that became part of the new Department of Homeland Security in March 2003 – is tasked with responding to, planning for, recovering from, and mitigating against disasters. FEMA is responsible for coordinating the federal response to floods, earthquakes, hurricanes, and other natural or man‐made disasters and providing disaster assistance to states, communities and individuals. FEMA administers the National Flood Insurance Program (NFIP) to provide subsidized flood insurance to communities that comply with FEMA regulations limiting development on floodplains. FEMA issues Flood Insurance Rate Maps (FIRMs) for communities participating in the NFIP, which delineate flood hazard zones.

State Regulations

The California State Water Resources Control Board (State Board) and the nine Regional Water Quality Control Boards (RWQCB) have the authority in California to protect and enhance water quality, both through their designation as the lead agencies in implementing the Section 319 non‐point source program of the federal Clean Water Act, and through the state’s primary water pollution control legislation, the Porter‐Cologne Act. The San Francisco (Region 2) office of the RWQCB guides and regulates water quality in streams and aquifers throughout the San Francisco Bay area, including Santa Clara County. The RWQCB implements the Basin Plan, which designates beneficial uses and establishes water quality objectives. The RWQCB also administers the NPDES permit program for storm water and construction site runoff, and is also responsible for providing permits under Section 401 of the CWA.

NATIONAL POLLULTION DISCHARGE ELIMINATION SYSTEM (NPDES)

Point source discharges to surface waters are generally controlled through waste discharge requirements issued under the federal National Pollutant Discharge Elimination System (NPDES) permits. Although the NPDES program was established by the federal Clean Water Act, the EPA has delegated management of California’s NPDES permit program to the State Water Resources Control Board and the nine regional (RWQCB) offices. Issued in five‐year terms, an NPDES permit usually contains components such as discharge prohibitions, effluent limitations, and necessary specifications and provisions to ensure proper treatment, storage, and disposal of the waste. The permit often contains a monitoring program that establishes monitoring stations at effluent outfall and receiving waters (California Regional Water Quality Control Board, San Francisco Bay Region, 2007).

TOWN OF LOS GATOS DRAFT EIR L INDA C OURT R ESIDENCES 4.3-2 JANUARY 2010 HYDROLOGY & WATER QUALITY

The 1987 amendments to the Clean Water Act (Section 402[p]) provided for the U.S. EPA regulation of several new categories of non‐point pollution sources within the existing NPDES). In Phase 1, NPDES permits were issued for urban runoff discharges from municipalities of over 100,000 people, from plants in industries recognized by the EPA as being likely sources of stormwater pollutants, and from construction activities that disturbed more than five acres. Phase 2 implementation, effective March 10, 2003, extended NPDES urban runoff discharge permitting to cities of 50,000 to 100,000, and to construction sites that disturb between 1 and 5 acres.

The Town of Los Gatos is part of the Santa Clara Valley Urban Runoff Pollution Prevention Program (SCVURPPP) that has been issued a National Pollutant Discharge Permit (NPDES) under the Clean Water Act for discharge of storm water runoff. The SCVURPPP is an association of thirteen cities and towns in the Santa Clara Valley, together with Santa Clara County and the Santa Clara Valley Water District that, share a common permit to discharge stormwater to South San Francisco Bay. Further discussion is provided below.

Construction activity on projects that disturb one or more acres of soil, or less than 1 acre but are part of a larger common plan of development that in total disturbs one or more acres, must obtain coverage under the General Permit for Discharges of Storm Water Associated with Construction Activity (Construction General Permit, 99‐08‐DWQ). Construction activity subject to this permit includes clearing, grading, and disturbances to the ground such as stockpiling or excavation, but does not include regular maintenance activities performed to restore the original line, grade, or capacity of a facility. The Construction General Permit requires the development and implementation of a Storm Water Pollution Prevention Program (SWPPP). The SWPPP should contain a site map(s) that shows the construction site perimeter, existing and proposed buildings, lots, roadways, storm water collection and discharge points, general topography (both before and after construction), and drainage patterns across the project. The SWPPP must list best management practices (BMPs) that the discharger will use to protect storm water runoff and the placement of those BMPs. Additionally, the SWPPP must contain a visual monitoring program and a chemical monitoring program for ʺnon‐visibleʺ pollutants to be implemented if there is a failure of BMPs.

PORTER-COLOGNE WATER QUALITY CONTROL ACT

Under the stateʹs Porter‐Cologne Water Quality Control Act, any person discharging or proposing to discharge waste within the region (except discharges into a community sewer system) that could affect the quality of the waters of the state is required to file a Report of Waste Discharge (ROWD). The Water Board reviews the nature of the proposed discharge and adopts Waste Discharge Requirements (WDRs) to protect the beneficial uses of waters of the state. Waste discharge requirements could be adopted for an individual discharge, or a specific type of discharges in the form of a general permit. The Water Board may waive the requirements for filing a ROWD or issuing WDRs for a specific discharge where such a waiver

TOWN OF LOS GATOS DRAFT EIR L INDA C OURT R ESIDENCES 4.3-3 JANUARY 2010 HYDROLOGY & WATER QUALITY

is not against the public interest. NPDES requirements may not be waived. Acceptable control measures for point source discharges must ensure compliance (California Regional Water Quality Control Board, San Francisco Bay Region, 2007).

CLEAN WATER ACT WATER QUALITY CERTIFICATIONS

Under section 401 of the federal Clean Water Act, the RWQCB has regulatory authority over actions in waters of the United States through issuance of water quality certifications, which are issued in combination with permits issued by the U.S. Army Corps of Engineers under section 404 of the Clean Water Act. When the Board issues section 401 certifications, it simultaneously issues general Waste Discharge Requirements for the project under the Porter‐ Cologne Water Quality Control Act.

Local Regulations and Programs

The Town of Los Gatos coordinates regulating the NPDES permit with the West Valley Clean Water Program (that includes Campbell, Los Gatos, Monte Sereno, and Saratoga), West Valley Sanitation District, and Santa Clara Valley Urban Runoff Pollution Prevention Program (SCVURPPP). To reduce pollution in urban runoff to the ʺmaximumʺ extent practicable, the Program incorporates regulatory, monitoring and outreach measures aimed at improving the water quality of South San Francisco Bay and the streams of the Santa Clara Valley. As part of the NPDES permit requirements, the Program produced (and updates) an “Urban Runoff Management Plan” and submits annual work plans and reports to the Regional Board.

SANTA CLARA VALLEY URBAN RUNOFF PREVENTION PROGRAM

In 1990, the SCVURPPP received the first municipal stormwater permit in the nation from the San Francisco Bay Regional Water Quality Control board, which was reissued the permit in 1995 and 2001. In 2001, the permit was amended to include expanded requirements for controlling pollutants from new development and redevelopment activities (Provision C.3), which was further amended in 2005 to allow for phased implementation of new requirements (SCVURPPP, 2008). In order to comply with the State‐issued NPDES permit, No. 01‐119, Los Gatos & other public agencies in the Santa Clara Valley are required to place additional Conditions of Approval related to storm water quality control on certain development projects. Non‐exempt projects creating or replacing 1 acre or more of impervious surface are subject to Group 1 Project requirements and Hydromodification Management Plan (HMP) requirements (designed to control volume and duration of stormwater runoff to prevent erosion of creeks and streams). Group 2 projects (between 10,000 square feet and one acre) of impervious surfacing must incorporate design, control and engineered treatment measures into drainage designs.

TOWN OF LOS GATOS DRAFT EIR L INDA C OURT R ESIDENCES 4.3-4 JANUARY 2010 HYDROLOGY & WATER QUALITY

WEST VALLEY CLEAN WATER PROGRAM

The West Valley Clean Water Program was established to represent the smaller west valley communities which include the cities of Campbell, Monte Sereno, Saratoga and the Town of Los Gatos. The West Valley Clean Water Program was established to guide the smaller west valley cities and towns on their requirements of the general NPDES permit and determine the applicable requirements of the permit to these smaller communities.

TOWN OF LOS GATOS

Chapter 12 of the Town Code regulates grading and erosion control. Chapter 12 establishes administrative procedures, minimum standards of review and implementation and enforcement procedures for the protection and enhancement of the water quality of watercourses, water bodies and wetlands, both natural and manmade. This is accomplished by controlling erosion, sedimentation, increases in surface runoff and related environmental damage caused by construction‐related activities (Design, Community and Environment, February 2009).

Article IX of Chapter 29 (Zoning Regulations) addresses floodplain management. Chapter 22 of the Town Code addresses stormwater pollution and control and establishes requirements for non‐standard stormwater discharges. Chapter 22 prohibits materials being discharged into the municipal storm drain system or watercourses other than stormwater, including any pollutants or waters containing any pollutants that cause or threaten to contribute to a violation of applicable water quality standards, and any sewage, industrial waste or other polluted waters or materials without a valid NPDES permit or written authority from the U.S. Environmental Protection Agency (EPA) or its designated enforcement agent. Section 22.30.035 includes requirements for new development and redevelopment projects.

On February 20, 2007, the Town of Los Gatos Town Council, as a participant in the Santa Clara Valley Water Resources Protection Collaborative, adopted the Guidelines and Standards for Land Use Near Streams that had been prepared by the Santa Clara Valley Water Resources Protection Collaborative (July 2006). In adopting these Guidelines and Standards (G&S), the Town Council directed that they be applied to future streamside development to the “extent feasible.” The Guidelines address land use activities near streams and provide guidelines and standards to protect surface and groundwater quality and for riparian protection.

SANTA CLARA VALLEY WATER DISTRICT

To manage and protect the valleyʹs water resources, the Santa Clara Valley Water District requires permits for all well construction and destruction work, most exploratory boring, and for projects or activities that occur on District fee title property or within District easement right‐of‐way or may have potential impacts to District facilities in Santa Clara county. Permits

TOWN OF LOS GATOS DRAFT EIR L INDA C OURT R ESIDENCES 4.3-5 JANUARY 2010 HYDROLOGY & WATER QUALITY

are required under two Santa Clara Valley Water District Ordinances: Water Resources 1 Protection Ordinance and 90‐1 (the District Well Ordinance).

REGIONAL HYDROLOGIC SETTING

The Town of Los Gatos is located south of the San Francisco Bay within the South Bay Drainage Unit. The South Bay Drainage Unit lies within the Coastal Range geomorphic province and is characterized by a broad alluvial valley sloping northward to the San Francisco Bay (Design, Community and Environment, February 12, 2009).

The project site is located adjacent to Ross Creek, which is a tributary to the Guadalupe River, located approximately 4 miles east of the project site. According to information on the Santa 2 Clara Valley Water District’s website, the Guadalupe watershed covers 170 square miles and includes Guadalupe River, Guadalupe Creek, Los Gatos Creek, Ross Creek, Alamitos Creek, and Canoas Creek. The watershed drains the Guadalupe River and its tributaries into the San Francisco Bay. The watershed includes the Town of Los Gatos and the cities of San Jose, Monte Sereno, Campbell and Santa Clara. There are 6 major reservoirs in the Guadalupe River watershed: Guadalupe Reservoir on Guadalupe Creek; Almaden Reservoir on Alamitos Creek; Vasona Reservoir, Lexington Reservoir, and Lake Elsman on Los Gatos Creek; and Calero Reservoir on Calero Creek. All of these reservoirs were constructed for water conservation and storage purposes, but can provide flood control benefits depending on the size of the upstream drainage areas and the available water storage capacities (Santa Clara Basin Watershed Management Initiative, 2003b).

The headwaters of the Guadalupe River spring from the eastern Santa Cruz Mountains. The highest point in this watershed is Loma Prieta (elevation 3,790 feet), which drains to both Los Gatos and Alamitos creeks (the latter via Barrett Canyon tributary). The Guadalupe River begins at the confluence of Alamitos and Guadalupe Creeks, below Almaden Lake and flows 19 miles through heavily urbanized portions of San Jose, ultimately discharging into South San Francisco Bay through Alviso Slough (California Regional Water Quality Control Board, San Francisco Bay Region, October 2008).

Three urban creeks—Ross, Canoas, and Los Gatos Creeks—join the river as it flows toward San Francisco Bay (California Regional Water Quality Control Board, San Francisco Bay Region, October 2008). Ross Creek drains an area of about 10 square miles before it joins the Guadalupe River just downstream of Branham Lane. Canoas Creek drains an area of about 19 square miles before joining the Guadalupe River just upstream of Curtner Avenue. Los Gatos

1 Santa Clara Valley Water District. 2002. “Permits.” Available online at: http://www.valleywater.org/Business_Info_and_Permits/Permits/index.shtm 2 Santa Clara Valley Water District. March 19, 2009. “Guadalupe Watershed.” Available online at: http://www.scvwd.dst.ca.us/water/Watersheds_-_streams_ and_floods/Watershed_info_&_proj

TOWN OF LOS GATOS DRAFT EIR L INDA C OURT R ESIDENCES 4.3-6 JANUARY 2010 HYDROLOGY & WATER QUALITY

Creek, with a drainage area of about 55 square miles, joins the Guadalupe River in downtown San Jose (Santa Clara Basin Watershed Management Initiative, 2003b).

The Guadalupe River has a total drainage area of approximately 170 square miles south of Highway 237. Tides influence the lower reach of the river as it flows for five miles through Alviso Slough to San Francisco Bay. When development of the salt ponds in the South Bay began in 1866, lower river flows were diverted from their original course through Guadalupe Slough to Alviso Slough. There are no natural deep lakes in the watershed; all reservoirs and percolation ponds (i.e., former gravel quarries, including Almaden Lake) are engineered impoundments (California Regional Water Quality Control Board, San Francisco Bay Region, October 2008).

The Guadalupe River watershed experiences a Mediterranean‐type climate generally characterized by wet, mild winters and dry summers. About 85% of the measurable precipitation, rainfall, occurs between November and April. Mean annual precipitation ranges from 48 inches in the headwaters above the Guadalupe and Almaden reservoirs to 14 inches in downtown San Jose (California Regional Water Quality Control Board, San Francisco Bay Region, October 2008).

The watershed’s Mediterranean‐type climate produces different flow characteristics for the Guadalupe River in the dry and wet seasons. Wet season flows can be large and episodic, while dry season flows are lower but more uniform. This pattern is also observed in the urban creeks, and differs with the more managed and less variable outflows from the reservoirs (California Regional Water Quality Control Board, San Francisco Bay Region, October 2008).

The Guadalupe River played an important role in the settlement of San Jose, and has been subject to considerable modification. The first major modification of the stream channel occurred in 1866 when a canal was dug to alleviate flooding and to improve conditions for rapidly expanding orchards (Santa Clara Basin Watershed Management Initiative, 2003b). About this time, the river was diverted from Guadalupe Slough to Alviso Slough. The New Almaden Mining District was in operation prior to 1866, so mercury‐laden sediment has likely accumulated in Guadalupe Slough and the adjacent salt ponds. In 1963, local agencies channelized the lower Guadalupe River and added new levees along Alviso Slough out to South San Francisco Bay. In the early 1960s, Canoas Creek and Ross Creek were rerouted to flow into the Guadalupe River at different locations, and the lower reaches of both creeks were channelized. As part of the 1975 Almaden Expressway construction project, about 3,000 feet of the Guadalupe channel were widened and moved eastward. The original stream channel was filled to allow the construction of the northbound expressway (California Regional Water Quality Control Board, San Francisco Bay Region, October 2008). According to the San Francisco RWQCB, these modifications affect sediment transport and locations where mercury‐laden sediment accumulates (Ibid.).

TOWN OF LOS GATOS DRAFT EIR L INDA C OURT R ESIDENCES 4.3-7 JANUARY 2010 HYDROLOGY & WATER QUALITY

SITE STORMWATER DRAINAGE

The project site slopes gently downward to the north toward Ross Creek. Site storm water runoff flows via sheet flow into the Creek. The Soil Conservation Service soil survey for Santa Clara County indicates that the soil is characterized as having low permeability, so it is expected that a good portion of the runoff from the site currently flows into Ross Creek with relatively little groundwater infiltration. Approximately 2.8 acres of land in the Linda Avenue neighborhood also drains toward and through the project site currently via sheet flow. Underground storm drains are intermittently located in this part of Los Gatos, and none are known to exist within the project neighborhood.

Ross Creek traverses the northern edge of the project site and is a tributary to Guadalupe River. Ross Creek extends northeast from near the northern base of the Sierra Azul east of Los Gatos and flows for approximately 6 miles through Los Gatos and urbanized portions of San Jose to the Guadalupe River just downstream of Branham Lane. Ross Creek drains an area of about 10 square miles and is fed by two tributaries: Short Creek and Lone Hill Creek as described below (Santa Clara Basin Watershed Management Initiative, 2003c). ‰ Lone Hill Creek is an intermittent stream that rises on the northern side of the Sierra Azul and flows north for a short distance into Ross Creek. Most of the creek’s channel is concrete‐lined as it flows through an urbanized area; however, its upper portion is in a relatively undeveloped foothill area (Ibid.). ‰ Short Creek is essentially the uppermost portion of Ross Creek (above Blossom Hill Road). Short Creek is an intermittent stream that rises on the northern side of the Sierra Azul and flows northwest and then curves north for a short distance into Ross Creek. Most of the creek’s channel is natural as it flows from undeveloped foothill areas down into a more urbanized area (Ibid.).

Ross Creek has been characterized as both intermittent (California Department of Fish and Game [April 2009], Santa Clara Basin Watershed Management Initiative [2003c]) and perennial (H.T. Harvey Associates [June 2008], Wood Biological Consulting [January 2007]). Ross Creek is a jurisdictional water of the U.S., subject to the jurisdiction of the USACE and the State Water Board under the authority of sections 404 and 401, respectively, of the federal Clean Water Act.

Ross Creek supports vegetation along its banks in the project vicinity as shown on the aerial 3 photo in Figure 4. However, approximately 1.5 miles upstream of the project site, the creek is either in a buried culvert or a concrete lined channel. Immediately downstream of the site, the creek continues to support a narrow bank of vegetation, then transitions into a concrete‐lined

3 All EIR figures are included in Chapter 7.0 at the end of the EIR (before appendices) for ease of reference as some figures are referenced in several sections.

TOWN OF LOS GATOS DRAFT EIR L INDA C OURT R ESIDENCES 4.3-8 JANUARY 2010 HYDROLOGY & WATER QUALITY

channel and thereafter enters a culvert (H.T. Harvey Associates, June 2008; California Department of Fish and Game, September 2008). As previously indicated, Ross Creek was rerouted to flow into the Guadalupe River at a different location and the lower reach was channelized in the early 1960s.

Within the project area, the Ross Creek channel is 8‐15 feet wide with a rocky/gravelly bottom and very little sediment (Wood Biological Consulting, January 2007). The southern creek bank that is located on the project site is a natural earthen bank. The northern creek bank is characterized by sack concrete, wooden retaining walls and loose concrete rip‐rap used for bank stabilization. Additionally, there is a perched storm drain culvert outlet protruding from the middle of the north bank that discharges directly into the channel. In a few areas the sack concrete wall offsite along the northern creek channel is failing and appears to be jeopardizing the stability of the upper bank (H.T. Harvey Associates, June 12, 2008). Evidence of erosion was observed during the hydrologic site visit along the channel banks, particularly on the north side opposite of that of the proposed development. The project site also is identified as having a moderate to slightly‐moderate erosion hazard (Nolan, January 1999).

According to a field review conducted by the California Department of Fish and Game (California Department of Fish and Game, April 2009). the stream is very “flashy” due to its course through a heavily urbanized watershed that is affected by urban runoff. It has exaggerated floodpeak responses to rainfall events because of the surrounding impervious surfaces that prevent soil saturation and instead direct all runoff directly into the creek. There is natural flow present that may extend to around Los Gatos‐Almaden Road during wet years; below this point the stream is usually dry by early to mid‐summer. The Santa Clara Valley Water District (SCVWD) adds imported water to the creek for percolation purposes via a pipeline that crosses the creek in the vicinity of Blossom Valley Road. This flow is managed so that it maintains flow down to a gauging station maintained by SCVWD at approximately Cherry Avenue. During the current two‐year drought, there has been no flow augmentation since last year due to reduced availability of imported water.

During a CDFG site visit in March 2009, there was evidence of recent above‐bankfull flows (California Department of Fish and Game, April 2009). It was also noted that the existing sackcrete was not posing any immediate threat to fish species or habitat in Ross Creek adjacent to the site, and removal or replacement may result in additional impacts to the stream and would not substantially benefit aquatic species as creek goes dry (Ibid.).

FLOOD HAZARDS

The FEMA Flood Insurance Rate Map (FIRM) indicates that the stream corridor is designated as a Zone A (Federal Emergency Management Agency, May 18, 2009, Panel 377 of 830 for Santa Clara County, California). This means that the flood extent is approximate and that a

TOWN OF LOS GATOS DRAFT EIR L INDA C OURT R ESIDENCES 4.3-9 JANUARY 2010 HYDROLOGY & WATER QUALITY

detailed study for the area has not been completed. The rest of the site is within a Zone D designation which means that flood hazards are possible but undetermined.

In order to determine the potential hazard from a 100‐year flood at the project site, Schaaf & Wheeler prepared a hydraulic analysis, which is included in Appendix E. The channel and floodplain downstream of the project site were modeled using the Corps of Engineers HEC‐ RAS computer model as part of the FEMA Flood Insurance Study for the City of San Jose. Since that model did not extend to the site, three new cross sections were surveyed through the project site to model Ross Creek in the vicinity of the site. The locations were chosen based on several criteria: the section needed to establish reach boundaries, be of indicative the particular portion of the reach, and be accessible for surveying (Schaaf & Wheeler, June 11, 2009).

There is a published 100‐year flow rate at Union Avenue of 1,200 cubic feet per second (cfs) for a drainage area of 4.0 square miles. Ross Creek was studied using detailed methods downstream of the project site as part of the FEMA Flood Insurance Study for the City of San Jose. The flowrates used in the study were based on a rainfall runoff model calibrated for most of the stream gage stations in the Bay Area. The model accounts for differences in mean annual precipitation, watershed area, and watershed slope and shape. The regional model methodology was used to estimate flows for ungaged watersheds, and to avoid depending on individual stream gages which may have poor records or anomalous statistical results (Schaaf & Wheeler, June 11, 2009).

Based on the USGS quadrangle map for the area, there is approximately 0.7 square miles of drainage area downstream of the Linda Avenue site to the Union Avenue crossing. Therefore, the District’s 100‐year flow rate of 1,210 cfs may be conservative compared to the FEMA estimate (Schaaf & Wheeler, June 11, 2009).

Three new cross sections were surveyed at the project site for use in the model. The location of the surveyed cross sections and the resulting 100‐year floodplain are shown on Figure 20. Since the FEMA flow is used in the analysis prepared for this EIR, the results constitute a more detailed study, allowing the floodplain to have elevations assigned and therefore be mapped with greater accuracy.

WATER QUALITY

As previously indicated, the project site is located within the Ross Creek watershed. Runoff from the site would discharge directly into Ross Creek, flow into the Guadalupe River, and eventually into the San Francisco Bay. The Guadalupe River is on the Clean Water Act Section 303(d) List of Water Quality Limited Segments due to the presence of diazinon (a pesticide)

TOWN OF LOS GATOS DRAFT EIR L INDA C OURT R ESIDENCES 4.3-10 JANUARY 2010 HYDROLOGY & WATER QUALITY

4 and mercury. Guadalupe Reservoir and Guadalupe Creek are also listed for mercury. If a waterbody exceeds the maximum allowable pollution level or fails to meet a recognized designated beneficial use, it is deemed “impaired” and a TMDL (Total Maximum Daily Load) must be developed to addresses the causes of impairment, sources of pollution, and necessary actions to restore the waterbody. To date, TMDLs have been developed for mercury for Guadalupe River, Guadalupe Creek, Alamitos Creek, Lake Almaden, and Guadalupe, Almaden and Calero Reservoirs.

The Guadalupe watershed has been identified as a significant mercury source to the San Francisco Bay due to historic mining of mercury ore within the watershed. Most of the mining activities occurred within what was once known as the New Almaden Mining District and is now the present location of the Almaden Quicksilver County Park. Mercury mining began in 1845 and occurred up to 1975, when the approximate 3,750‐acre area was purchased by Santa Clara County for use as a recreational park. Seventy‐five percent of the total park area drains into the Guadalupe River via intermittent creeks and perennial streams. The remaining area drains into the Guadalupe and Almaden reservoirs (Santa Clara Basin Watershed Management Initiative, 2003b). Erosion and runoff from calcine piles, waste rockpiles (unprocessed rock), and road material cause mercury‐laden sediment to be transported into nearby surface waterbodies (Ibid.).

GROUNDWATER MANAGEMENT

Local groundwater supplies up to half of Santa Clara County’s water supply during average years and nearly all of the water demand in south Santa Clara County. The Santa Clara Valley Water District (SCVWD) manages three groundwater sub‐basins that transmit, filter, and store water: the Santa Clara Valley, Coyote Valley, and Llagas sub‐basins. The District’s active conjunctive water management program uses surface water in conjunction with groundwater to optimize the use and management of water supply sources. Surface water is treated for distribution (reducing direct demands on groundwater) and is also banked in local sub‐basins through managed recharge so that groundwater can be withdrawn when needed. Conjunctive use also helps protect local sub‐basins from overdraft, land subsidence, and saltwater intrusion and provides critical groundwater storage reserves for use during droughts or outages. Conjunctive use management is an important tool that allows the groundwater basin to be pumped more in drier years and then replenished (or recharged) during wet and average years (Santa Clara Valley Water District, December 20, 2005).

The Town of Los Gatos is located within the Santa Clara Valley Groundwater sub‐basin (Design, Environment and Community, February 2009). The Santa Clara Valley Sub‐basin is

4 California Water Resources Control Board. 2007. “2006 Board Approved of Clean Water Act Section 303(d) List of Water Quality Limited Segments.” Found online at: http://www.waterboards.ca.gov/water_issues/programs/tmdl/303d_lists2006.shtml

TOWN OF LOS GATOS DRAFT EIR L INDA C OURT R ESIDENCES 4.3-11 JANUARY 2010 HYDROLOGY & WATER QUALITY

located in a structural trough that is bounded by the Santa Cruz Mountains to the west and the Diablo Range to the east. The sub‐basin, which is approximately 22 miles long, narrows from a width of 15 miles near the county’s northern boundary to about half a mile wide at the Coyote Narrows, where the two ranges nearly converge. The sub‐basin has a surface area of 225 square miles (Santa Clara Valley Water District, December 20, 2005). It appears that the southwestern edge of the sub‐basin.

The Santa Clara Valley Sub‐basin is approximately 15 square miles smaller than the Santa Clara Sub‐basin (Basin 2‐9.02) as defined by the DWR in Bulletin 118, Update 2003, which includes the Coyote Sub‐basin. Although hydraulically connected, the District refers to the Coyote Sub‐basin separately (Santa Clara Valley Water District, December 20, 2005).

The District estimates the long‐term operational storage capacity of the Santa Clara Valley Sub‐basin to be 350,000 acre‐feet. In any given year the amount of groundwater that can be withdrawn depends on current groundwater conditions and hydrology. To avoid reinitiation of land subsidence, the District has determined that groundwater withdrawals in the Santa Clara Valley Subbasin should not exceed 200,000 acre‐feet in any one year. The District defines operational storage capacity as the volume of groundwater that can be stored in a basin or subbasin as a result of District management measures. Operational storage capacity is generally less than total storage capacity as it accounts for the avoidance of land subsidence and high groundwater conditions, as well as available pumping capacity. (Santa Clara Valley Water District, December 20, 2005).

Replenishment of groundwater withdrawn from operational storage depends on local hydrology and extra supply for additional recharge which could take many years. Groundwater is replenished both naturally from rainfall and augmented by District‐operated recharge facilities and streams. The SCVWD operates and maintains 18 major recharge systems, which consist of both in‐stream and off‐stream facilities. Most of this local supply is recharged into the groundwater subbasins, either through natural stream channels, through canals, or through in‐stream and off‐stream ponds. Local runoff is captured in local reservoirs for recharge into the groundwater subbasins or treatment at one of the District’s water treatment plants. The total storage capacity of these reservoirs is about 170,000 acre‐feet. (Santa Clara Valley Water District, December 20, 2005).

REGIONAL AND LOCAL PLANS

Basin Plan

The “Water Quality Control Plan for the San Francisco Bay Basin (Basin Plan)” is the Regional Water Quality Control Boardʹs master water quality control planning document. It designates beneficial uses and water quality objectives for waters of the State, including surface waters

TOWN OF LOS GATOS DRAFT EIR L INDA C OURT R ESIDENCES 4.3-12 JANUARY 2010 HYDROLOGY & WATER QUALITY

and groundwater. It also includes programs of implementation to achieve water quality objectives. The Basin Plan has been adopted and approved by the State Water Resources 5 Control Board, U.S. EPA, and the Office of Administrative Law where required.

The San Francisco RWQCB regulates water quality in the project area in accordance with the Water Quality Control Plan or “Basin Plan” (California Regional Water Quality Control Board, San Francisco Region, 2007). Beneficial uses are identified for all tributaries of a water body (including groundwaters, marshes, mudflats, and surface waters within a watershed). Water quality objectives and criteria that must be met to protect these uses are presented in the plan. Beneficial uses of water bodies in the Guadalupe watershed are summarized in Table 2‐2. Neither Ross Creek nor Guadalupe River is not included in the list, only Guadalupe Reservoir.

TABLE 2-2: Beneficial Uses of Surface Water Bodies – Guadalupe Watershed

Water Body Beneficial Uses in the Basin Plan GuadalupeReservoir ‐ MUN, GWR,COLD, WARM, WARM, WILD, REC‐2 Existing Guadalupe Reservoir ‐ MIGR, SPWN, REC1 Potential Source: California RWQCB, San Francisco Bay Region, Basin Plan. Beneficial Use Definitions: Municipal and Domestic Supply (MUN); Agricultural Supply (AGR); Industrial Service Supply (IND); Ground Water Recharge (GWR); Freshwater Replenishment (FRSH); Water Contact Recreation (REC‐1); Non‐Contact Water Recreation (REC‐2); Commercial and Sport Fishing (COMM); Warm Fresh Water Habitat (WARM); Cold Fresh Water Habitat (COLD); Wildlife Habitat (WILD), Preservation of Biological Habitats of Special Significance (BIOL); Rare, Threatened, or Endangered Species (RARE); Migration of Aquatic Organisms (MIGR); Spawning, Reproduction, and/or Early Development (SPWN).

Watershed Management Initiative

In 1996, the State Water Resources Control Board and the U.S. EPA initiated an effort to encourage local stewardship in the Santa Clara basin as part of the statewide “Watershed Management Initiative” (WMI). The Santa Clara basin is defined as the San Francisco Bay south of the Dumbarton Bridge and the watersheds draining to that segment of the Bay. The Santa Clara Basin Watershed Management Initiative is a broad‐based stakeholder group of 32 signatories from local, state and federal public agencies, business and trade associations, and civic and environmental groups and programs. The declared purpose of this WMI is ʺto develop and implement a comprehensive watershed management program ‐ one that recognizes that healthy watersheds mean addressing water quality problems and quality of

5 From website of the California Regional Water Quality Control Board, San Francisco Region, 2007. Online at: http://www.waterboards.ca.gov/sanfranciscobay/basin_planning.shtml

TOWN OF LOS GATOS DRAFT EIR L INDA C OURT R ESIDENCES 4.3-13 JANUARY 2010 HYDROLOGY & WATER QUALITY

life issues for the people, animals and plants that live in the watershed.ʺ The WMI established a mission statement, goals, planning objectives for development of a watershed action plan, implementation objectives, and a framework for conducting a watershed assessment. To date, he Santa Clara Basin WMI has prepared watershed assessments (2002) and a watershed action plan (2003).

Stream Guidelines and Standards

As previously indicated, the Town of Los Gatos Town Council, as a participant in the Santa Clara Valley Water Resources Protection Collaborative, adopted the Guidelines and Standards for Land Use Near Streams, prepared by the Santa Clara Valley Water Resources Protection Collaborative (July 2006). These Guidelines and Standards (G&S) provide definitions of streams and associated features, and identify guidelines and standards that address a number of riparian, hydrologic and land use issues that include: drainage, bank stability and encroachments, grading and erosion, outfall design, water quality, groundwater protection and flood protection.

The Guidelines and Standards also identify approximately twenty specific design guidelines related to: riparian vegetation protection, use of native and non‐native species, erosion control, slope stability, fill and plantings by levees, grading, outfall standards, species for buffers and swales, trail design, utility crossings, groundwater assessment, detention basin design, and bank protection/repair guide.

A full review of the project for consistency with these guidelines is included in Appendix F. With regards to drainage and other hydrologic issues, the review found that the project is consistent with the guidelines. Runoff is not directed outside of the watershed. Drainage is directed to bioswales and bioretention for pre‐treatment prior to discharge into Ross Creek as further described below. No culverting, fill or modification of Ross Creek is proposed. Preliminary outfall designs appear consistent with the Stream Guidelines (Conran, personal communication, December 2009); final designs for the proposed outfall will be required to meet “Design Guide 12” guideline of the Santa Clara Valley Water Resources Protection Collaborative’s “Guidelines for Land Use Near Streams.” Based on a hydraulic study conducted for this EIR and as described below, project structures will not be located within a 100‐year floodplain.

RELEVANT PROJECT ELEMENTS

The project consists of a Planned Development approval to construct 7 single‐family homes and demolish existing onsite structures (a single‐family home and cottage). According to the project plans, the proposed building footprints and other impervious surfacing covers approximately 32,998 square feet. This represents 32% of the project site or approximately 40%

TOWN OF LOS GATOS DRAFT EIR L INDA C OURT R ESIDENCES 4.3-14 JANUARY 2010 HYDROLOGY & WATER QUALITY

of the net developable area (excluding dedications and creek area). Proposed impervious and pervious surfacing are shown on Figure 18. According to the project landscaping plan, driveways will be a mix of pervious paving and porous concrete; proposed pervious pavement totals 3,000 square feet.

The project includes approximately 25,470 square feet of common open space area (excluding the street, parking and walkways).. The common area includes an open space area located between proposed Lots 3 and 4, as well as a riparian area adjacent to Ross Creek (as shown on Figure 5) in addition to landscaping. Approximately 9,640 square feet of riparian habitat along Ross Creek will be dedicated to the Town of Los Gatos. An additional adjacent 9,728 square feet is proposed as an easement to be dedicated to the Santa Clara Valley Water District.

The proposed project drainage plan consists of a system of grassy swales on each residential lot, a bioretention system, and new storm drain with a new discharge outfall to Ross Creek. Runoff from each home lot (i.e., roofs) will be conveyed to an onsite swale (approximately 2 feet wide and 6 inches deep). Lots 1, 2, 3, 6, and 7 will drain to a new 6‐inch PVC storm drain that will connect to a storm drain in the northeast corner of the site. Runoff from Lots 4 and 5 will flow to the proposed common area between proposed Lots 3 and 4, and discharged through a proposed rock energy dissipater.

Road runoff will be discharged to a bioretention swale for pretreatment prior to discharge into the creek. The bioretention swale, which is located along the northern edge of proposed Lots 1 and 2, is approximately 160 feet long, 5 feet wide and 6.5 feet deep. This bioretention feature is proposed to be underlain by a rock trench with subdrain and lined with native bunch grasses. The bioretention system will permit local filtration and percolation of project runoff prior to conveyance into a 15‐inch RCP storm drain in the northeastern corner of the site that will discharge into Ross Creek. Drainage system design details are shown on Figure 17.

The proposed outfall structure will extend 24 feet (4.5 feet within the creek bed, 15.5 feet along the slope, and 4 feet at the top of the bank). Geotextile fabric and rock will be placed with grout on the outer creek slope to anchor the storm drain. Outfall details are shown on Figure 17.

According to the project “Grading and Drainage Plan,” approximately 4,965 cubic yards of material will be excavated, of which 3,150 will be used for fill.

TOWN OF LOS GATOS DRAFT EIR L INDA C OURT R ESIDENCES 4.3-15 JANUARY 2010 HYDROLOGY & WATER QUALITY

IMPACTS AND MITIGATION MEASURES

CRITERIA FOR DETERMINING SIGNIFICANCE

In accordance with the California Environmental Quality Act (CEQA), State CEQA Guidelines, Town of Los Gatos polices, and professional standards, a project impact would be considered significant if the project would:

3a. Substantially deplete groundwater supplies or interfere substantially with groundwater recharge; 3b. Substantially alter the existing drainage pattern of the site or area or result in offsite drainage or flood problems; 3c. Substantially increase the rate or amount of surface runoff which would exceed capacity of existing or planned storm drain facilities, cause downstream or offsite drainage problems, or increase the risk or severity of flooding in downstream areas; 3d. Violate any water quality standards or waste discharge requirements or otherwise substantially degrade surface water quality; 3e. Result in construction of habitable structures within a 100‐year floodplain as mapped on a Federal Flood Hazard Boundary or Flood Insurance Rate Map or other flood hazard delineation map, which would expose people or structures to a significant risk of loss, injury or death due to flooding; 3f. Locate structures within a 100‐year flood hazard area that would impede or redirect flood flows; 3g. Expose people or structures to a significant risk of loss, injury, or death involving flooding as a result of the failure of a levee or dam; and/or 3h. Expose people or structures to a significant risk of loss, injury or death as a result in inundation by seiche, tsunami, or mudflow.

IMPACT ANALYSIS

Impacts assessed in the following section include impacts related to drainage (3b, 3c), water quality (3d), and flooding (3e, 3f). The Initial Study (see Appendix A) found no impacts for the other related impact criteria. The project would not result in impacts related to violations of waste discharge requirements (3a) as project wastewater will be discharged into the sanitary sewer system for conveyance to the regional wastewater treatment facility. However, The project’s storm water discharge into Ross Creek will require approval of a discharge permit from the Regional Water Quality Control Board; water quality impacts are addressed below. No impacts were identified in the Initial Study for exposure to flooding due to dam failure (3g) or tsunami (3h).

TOWN OF LOS GATOS DRAFT EIR L INDA C OURT R ESIDENCES 4.3-16 JANUARY 2010 HYDROLOGY & WATER QUALITY

Drainage

Impact 3A-1: Project development will result in increased runoff, but the proposed system is adequately designed to handle increased flows. This is considered a less-than-significant impact.

According to the project site plans, impervious surfacing on the project site would increase from approximately 6,900 to 32,998 square feet with the proposed building footprints (including garages), street, and patio decks. Impervious surfaces would cover an estimated 32% of the site. The increase in onsite impervious surfacing would increase runoff. Post‐ construction drainage calculations prepared by the applicant’s engineer are included in Appendix E.

The NPDES Provision C.3) requires post‐construction stormwater quantity controls (flow peak, volume and duration) for projects in specified locations that have 1 acre of more of impervious surfaces. Generally, post‐project runoff cannot exceed pre‐project levels, and the project drainage system must be designed so that post‐project runoff does not exceed pre‐ project levels. The proposed project’s 32,998 square feet of impervious surfacing is less than the 1‐acre requirement so the C.3 provisions for projects greater than 1 acre do not apply. However, the project’s impervious surfacing is greater than 10,000 square feet and under the C.3 provision, post‐construction stormwater treatment measures are required as further discussed below in Impact 3B.

A preliminary review of the proposed drainage system and runoff calculations was conducted by Schaaf & Wheeler as part of this EIR (see Appendix E), which included a review of the applicant’s drainage calculations (see Appendix E). The initial review identified potential inconsistencies between the calculations and site plans, as well as potential errors in the drainage subareas. At the request of the Town staff, the applicant revised the project site plan and grading and drainage plan. The final revised drainage plan was reviewed by Schaaf & Wheeler in December2009 (see Appendix E). . The review concluded that the sizing and preliminary design of the storm water treatment meet the Santa Clara Valley Urban Runoff Pollution Prevention Program standards as well as NPDES permit requirements (see Appendix E).

Overall the drainage system design and capacity appears adequate to handle post‐project flows, including the capacity of the onsite swales and bioretention swale. According to the project grading and drainage plan, the bioretention system is designed with a capacity of 1,445 cubic feet (cf) that exceeds the project runoff design volume of 1,393 cf. Therefore, the planned drainage system is adequately sized and designed to handle post‐project runoff volumes, the drainage impact related to increased runoff is considered less‐than‐significant.

TOWN OF LOS GATOS DRAFT EIR L INDA C OURT R ESIDENCES 4.3-17 JANUARY 2010 HYDROLOGY & WATER QUALITY

The increased runoff into Ross Creek is not expected to adversely affect creek channel conditions. Velocities are high in the Ross Creek channel, making the channel susceptible to erosion, and evidence of erosion can be seen along the channel banks, particularly on the north side opposite the proposed project. However, this is an existing condition and will not be exacerbated by the development. Since there is no encroachment of the 100‐year floodplain (as discussed further below) and all outfalls will be protected through the use of energy dissipaters, erosion potential will not be affected by runoff from the development (Schaaf & Wheeler, June 11, 2009). Preliminary outfall designs appear consistent with the Stream Guidelines (Conran, personal communication, December 2009); final designs will be required to meet “Design Guide 12” guideline of the Santa Clara Valley Water Resources Protection Collaborative’s “Guidelines & Standards or Land Use Near Streams.”

Mitigation Measures

No mitigation measures are required, but the following Condition of Approval is recommended.

‰ Recommended Condition of Approval. Final drainage plan design details shall include outfall details that conform to Design Guide 12 of the Santa Clara Valley Water Resources Protection Collaborative’s “Guidelines for Land Use Near Streams.”

Water Quality

Impact 3B-1: Project development will result in increased runoff that could indirectly affect water quality in Ross Creek. However, with implementation of the proposed bioretention system, water quality impacts would be minimized. This is considered a less-than-significant impact.

The project proposes one new outfall into Ross Creek. Stormwater runoff from the project site has the potential to contribute non‐point‐source pollutants, such as oil and grease, suspended solids, metals, gasoline, pesticides, and pathogens, to Ross Creek and downstream drainage systems. Water quality conditions within Ross Creek are influenced by pollutants frequently associated with stormwater runoff, including sediment, nutrients, oil and grease, heavy metals, and litter. The primary sources of stormwater pollution in urban areas typically is runoff from roads and parking lots, landscape maintenance, construction, accidental spills, and illegal dumping.

NPDES requirements include compliance with Provision C.3, New and Redevelopment Performance Standards, including incorporating appropriate source control and site design measures and to design and implement stormwater treatment measures to reduce the discharge of pollutants to the maximum extent practicable (Order No. 01‐024 of the NPDES as

TOWN OF LOS GATOS DRAFT EIR L INDA C OURT R ESIDENCES 4.3-18 JANUARY 2010 HYDROLOGY & WATER QUALITY

amended by Order No. 01‐119 and Order No. R2‐2005‐0035). Site design, source control and stormwater treatment BMPs, including pesticide reduction measures, are outlined by the SCVURPPP in its C.3 Stormwater Handbook. Stormwater treatment BMPs include bioretention, infiltration, and media filter with absorption.

The proposed project drainage plan includes a pre‐treatment system of grassy swales on each lot and a biorention system to filter road runoff prior to discharge into Ross Creek. Additionally, some portion of the proposed driveways and other non‐road pavement would be constructed of pervious materials. With these measures, runoff would be pre‐treated to filter out contaminants such as those identified above, so that pollutants would not enter the creek system. The proposed system design and bioretention features are consistent with the intent and requirements of the NPDES Provision C.3 according to the review conducted for this EIR (see Appendix E). With the proposed pre‐treatment features, the project’s impact on water quality is considered less than significant.

Mitigation Measures

None are required, but the following Condition of Approval is recommended to ensure adequate maintenance and functioning of the onsite bioretention system.

‰ Recommended Condition of Approval. To ensure regular inspection and maintenance, the project’s CC&Rs shall require Regular inspection and maintenance of the bioswales and drainage system improvements consistent with the Town of Los Gatos “Engineering Design Standards.”

Impact 3B-2: Project grading, construction and stormwater outfall installation could inadvertently result in erosion and sedimentation into Ross Creek. This is considered a potentially significant impact.

Site grading and installation of the storm drain outfall could result in erosion and water quality degradation in Ross Creek if not properly managed. According to the project “Grading and Drainage Plan,” approximately 4,965 cubic yards of material will be excavated, of which 3,150 will be used for fill. Additionally, the project includes installation of a new stormwater outfall into Ross Creek. The installation of the outfall will temporarily disturb 1,040 square feet creek bank (H.T. Harvey & Associates, June 2008), but no construction work is proposed in the creek channel.

Installation of the new stormwater discharge outfall, in addition to overall onsite grading, could result in inadvertent transport of sediments and other debris into the Ross Creek channel, thus, potentially indirectly affecting water quality. The project site slopes gently toward Ross Creek. However, due to the proximity of the construction sites to the creek,

TOWN OF LOS GATOS DRAFT EIR L INDA C OURT R ESIDENCES 4.3-19 JANUARY 2010 HYDROLOGY & WATER QUALITY

installation of drainage outlets and grading activities could result in significant erosion and water quality impacts.

All projects disturbing one or more acre of land during construction need to obtain coverage under the State’s “General Permit for Storm Water Discharges Associated with Construction Activity,” including preparation of a Stormwater Pollution Prevention Plan and erosion control measures. As a condition of project approval, the Town will require: (1) preparation and submittal of interim and final erosion control plans to the Engineering Division of the Parks and Public Works Department; and (2) implementation of non‐point source pollution prevention measures to reduce pollutant levels in the water that will eventually discharge to Ross Creek and Guadalupe River. With implementation of these measures, as well as the proposed drainage plan designs, the project would not result in significant water quality impacts.

Mitigation Measures

Implementation of Mitigation Measure 3B‐1 will reduce the impact to a less‐than‐significant level.

3B‐1 Implement erosion control measures, including, but not limited to: ‰ Require temporary fencing on the outer edge of the riparian vegetation canopy during construction to prevent inadvertent erosion, sedimentation, and/or construction debris from entering the adjacent riparian area or Ross Creek. Prohibit construction activities, placement of spoils, and storage of materials and machinery in the riparian setback. ‰ Provide adequate erosion control protection in the area of the drainage outlets, such as use of silt fences, straw bale barrier or other protective measures. ‰ Conduct grading work prior to the rainy season; protect disturbed areas during the rainy season; and contain and/or properly de‐water accumulated construction‐related runoff from disturbed areas or excavated areas. ‰ Restrict the timing of installation of the drainage outlets to the periods outside the rainy season (generally June 1 – September 30). ‰ Immediately revegetate disturbed areas. Apply weed‐free mulch or revegetate all soil exposed as a result of the proposed grading before November 1st of each year. ‰ Inspect and repair/maintain all erosion control measures prior to and after any rainfall event exceeding ½ inch, at 24‐hour intervals during

TOWN OF LOS GATOS DRAFT EIR L INDA C OURT R ESIDENCES 4.3-20 JANUARY 2010 HYDROLOGY & WATER QUALITY

extended storm events, and a minimum of every two weeks after the winter storm season. ‰ Locate staging and storage areas for equipment, materials, fuels, lubricants and solvents, at least 100 feet from Ross Creek. Locate oil absorbent and spill containment materials on site when mechanical equipment is in operation with 100 feet of the creek.

Flood Hazards

Impact 3C-1: Project development is located adjacent to Ross Creek, but will not be exposed to significant flood hazards and will not substantially increase flow elevations in Ross Creek. This is considered a less-than-significant impact.

The proposed new single‐family homes would not be located within the 100‐foot floodplain of Ross Creek according to the hydraulic analysis conducted for this EIR (see Appendix E). As shown on Figure 20, none of the structures are located within the 100‐year floodplain of Ross Creek. The results of the hydraulic analysis show that the calculated water surface elevations are below the elevation of the bottom of the proposed retaining wall at the back of the building lots. Therefore, since the wall will not encroach into the 100‐year floodplain area, the cross sectional geometry is not altered through the flow area resulting in no hydraulic change, as shown for Cross Section 1 in Appendix E.

The development will have minimal effect on the water surface elevation or velocity in the channel. Additional flows due to site development were not considered since the area of the site is minute in comparison with the contributing watershed area. The property is approximately 2.4 acres whereas the contributing drainage area is 4 square miles. Therefore, the property comprises 0.09% of the total watershed, or approximately one thousandth. Development of such a tiny portion of the watershed would produce a negligible, if any, increase in peak runoff.

Additionally, the hydraulic study used a published flow rate of 1,200 cfs for a drainage. The increased runoff generated by the project is estimated at 3 cfs, which would not be considered a significant flow increase.

Mitigation Measures

None are required.

TOWN OF LOS GATOS DRAFT EIR L INDA C OURT R ESIDENCES 4.3-21 JANUARY 2010