4.10 Hydrology and Water Quality 4.10 HYDROLOGY AND WATER QUALITY This section presents existing conditions, evaluates the impacts to hydrology and water quality associated with implementation of the 2050 RTP/SCS and identifies mitigation measures for significant impacts. The information presented was compiled from multiple sources, including Project Clean Water (PCW), the Regional Comprehensive Plan (RCP), and the Regional Water Quality Control Board (RWQCB). 4.10.1 EXISTING CONDITIONS Hydrology Watersheds and Hydrological Characteristics The San Diego region is divided into two hydrologic regions by the northwest-trending Peninsular Range. On the gently sloping western side of the range is the San Diego Hydrologic Region, and on the steep eastern side is the Colorado Hydrologic Region. Each hydrologic region is further divided into hydrologic units (HUs) that are defined as an entire watershed of one or more streams. Each HU is divided into hydrologic areas (HAs), which are the major tributaries and/or major groundwater basins within the HU, and further divided into hydrologic subareas (HSAs), which are major subdivisions of HAs including both water-bearing and non-water-bearing formations. Surface waters in the San Diego region include the ocean shoreline, bays, lagoons, lakes, reservoirs, streams, and rivers (Figure 4.10-1). Forecasted 2050 RTP/SCS associated development spans both the San Diego Hydrologic Region and the Colorado River Basin Hydrologic Region. The San Diego Hydrologic Region includes 11 HUs, and the San Diego region includes all of the Carlsbad, San Dieguito, Peñasquitos, San Diego, Pueblo, Sweetwater, and Otay watersheds; the majority of the San Luis Rey watershed; and portions of San Juan, Santa Margarita, and Tijuana watersheds. All of the watersheds in the San Diego Hydrologic Region ultimately drain to the Pacific Ocean. Figure 4.10-2 shows the watersheds and the groundwater basins. Characteristics of each watershed in the San Diego Hydrologic Region include the following (refer to Table 4.10-1 for a complete 2006 Clean Water Act Section [CWA] 303(d) list for all of the watersheds): • The San Juan watershed (HAs 901.1 to 901.5) covers approximately 496 square miles of which only 150 square miles lie in the northwest portion of the San Diego region. Most of the watershed lies within Marine Corps Base Camp Pendleton (MCBCP) in Orange and Riverside counties. Two of its hydrological areas are within the San Diego region (San Onofre and San Mateo). Major stream systems include the San Onofre, Las Flores, and Aliso Canyon creeks, which are usually dry from July through November. Topography varies from Pacific Ocean coastal plains to the Santa Margarita Mountains (over 2,000 feet above mean sea level [AMSL]). Various wildlife species use the undeveloped, low-lying creeks and streambeds as corridors to range freely within MCBCP and eastward into higher elevations. This portion of the San Juan watershed is largely undeveloped because of federal ownership. The land uses include open space, military base operations, and agriculture. Past water quality monitoring has indicated that the region’s surface waters are high in total dissolved solids (TDS) (PCW 2010). San Mateo Canyon HA at the San Mateo Creek outlet to the Pacific Ocean is on the 303(d) list impaired for total coliform (SDRWQCB 2006). • The Santa Margarita River watershed (HAs 902.1 to 902.9) encompasses approximately 750 square miles of which only 200 square miles lie in the northern San Diego region. Most of the SANDAG 2050 RTP/SCS EIR 4.10-1 JuneOctober 2011 4.10 Hydrology and Water Quality flow from the Santa Margarita River main stem is within the San Diego region and traverses through unincorporated areas, the community of Fallbrook, and MCBCP. The lower river and estuary at the Pacific Ocean coast remain less developed than other municipal coastlines to the south and, as a result, support abundant habitat and wildlife. Presently, the Rainbow Creek tributary is on the 303(d) list for an impairment of iron, sulfates, and TDS (SDRWQCB 20092006). The lower Santa Margarita River is listed on the 303(d) list impaired for enterrococcus, fecal coliform, phosphorus, and total nitrogen (SDRWQCB 20092006). These water bodies have been subject to excessive inputs of nutrients from a variety of sources including agriculture, nursery operations, municipal wastewater discharges, urban runoff, septic systems, and golf course operations (PCW 2010). Other serious water quality and environmental concerns in the watershed include excessive sedimentation from development and agricultural areas, groundwater degradation and contamination with nitrates and other salts, habitat loss, channelization, flooding, and scour (PCW 2010). • The San Luis Rey River watershed (HAs 903.1 to 903.3) is the second largest HU in the San Diego region (558-square-mile drainage). Situated in the northwestern portion of the San Diego region, the basin has two major surface waters, the San Luis Rey River and Lake Henshaw, and is divided into three HAs: the lower San Luis, Monserate, and Warner Valley. Roughly one-fourth of the land area in the watershed is located west of I-15, where land uses include open space/undeveloped, residential, commercial/industrial, and agricultural. East of I-15, most of the land is owned and managed by government agencies (county, state, and federal), special districts, and tribal governments. The predominant land uses are open space/undeveloped and agricultural. Unlike most major rivers in Southern California, the San Luis Rey River has undergone relatively little channelization (PCW 2010). The only significant segment of the river that has been channelized is within the City of Oceanside where it then drains into the Pacific Ocean. The lower San Luis Rey River is on the 303(d) list for an impairment of chloride, enterococcus, fecal coliform, phosphorus, TDS, total nitrogen, and toxicity (SDRWQCB 2009). • The Carlsbad watershed (HAs 904.1 to 904.6), extending from the headwaters above Lake Wohlford to the Pacific Ocean, is approximately 210 square miles in area. Within the watershed there are four major roughly parallel HAs: the Buena Vista, the Agua Hedionda, the Batiquitos, and the San Elijo. Each HA drains into the Pacific Ocean through creeks and rivers to discrete coastal lagoons. There are also two large water reservoirs, Lake Wohlford and Dixon Lake. Approximately 48 percent of the Carlsbad watershed is urbanized and its population ranks it as the third mostly densely populated in San Diego County (PCW 2010). As a result of this high urbanization, many of the water bodies are experiencing impairments to beneficial uses. The coastal lagoons represent critical regional resources that provide freshwater and estuarine habitats for numerous plant and animal species. Effective planning measures will be needed to prevent this rapid development from further degrading water quality in this region of San Diego County (PCW 2010). • The San Dieguito River watershed (HAs 905.1 to 905.5) comprises a drainage area of approximately 346 square miles in the west-central San Diego region, with most of the watershed (79.8 percent) situated in unincorporated jurisdiction that is mostly vacant or undeveloped (54 percent) (PCW 2010). Extending from the Volcan Mountains to San Dieguito Lagoon at the Pacific coastline, several natural areas within the watershed are sustained that include the San Dieguito River Park; San Dieguito Lagoon; and three water storage reservoirs— Lake Hodges, Lake Sutherland, and Lake Poway. Ocean waters along coastline at the mouth of the San Dieguito River are associated with elevated coliform bacteria. San Dieguito Lagoon is especially sensitive SANDAG 2050 RTP/SCS EIR 4.10-2 JuneOctober 2011 Temecula Orange County Aª Case Spring Riverside County Lake Rainbow San Diego County !"a$ Camp Pendleton Fallbrook North Mountain Aª O'neill Clark Lake Lake Palo Santa Verde Luis Rey Wash Margarita River Fonts River Pilgrim Bonsall Point Creek A¨ Wash !"^$ Lake Chimney Ella Valley Center Lost Lake Wash Whelan Guajome Pala-Pauma Lake Lake Lake Lake Turner Henshaw Borrego A¨ Lake Sink Wash North County Vista Metro Borrego Sink Pechstein Calavera Reservoir Oceanside Lake Buena A© San Lake Vista Dixon Squires Lake Wohlford Lagoon Marcos Benson Dam Escondido Lake Agua Lake San Hedionda Aª Marcos Lake Lake Carlsbad San Sutherland A© Marcos A© Julian Halfhill Batiquitos Lake Lake Lagoon Hodges Ramona San Dieguito Encinitas !"^$ San A© Dieguito Res. Desert San Elljo Lagoon Solana Beach !"a$ Figure 4.10-1 Lake Imperial County Poway Cuyamaca Barona County of San Diego Major Surface Waters Del Mar San Sewage Vincente Disposal Res October 2011 Ponds Miramar Central Mountain Lake El Capitan Lakeside Reservoir Aª Big Water Bodies Laguna %&s( Lake 303(d) Water Bodies ?z Lake Alpine Santee Jennings ?h Santee Areas of Special Biological Significance (ASBS) Recreational Mountain Empire San Lakes !"_$ Crest-Dehesa Rivers/Streams !"^$ Diego Murray Sweetwater Lake Reservoir A× El 303(d) Rivers/Streams Aù Mt Helix Cajon Reservoir Loveland Res !"_$ La Valle De Oro Corte Mesa Madera AÀ Lemon Grove Spring Valley ?Þ Henry Sweetwater Jamul-Dulzura Jr. Dam Morena Sweetwater Res. Res A§National Tule Barrett Lake City ?j AÀ Lake Coronado Upper Otay A× Reservoir AÀ Chula Lake Lower Campo Domingo Vista Otay Lake Salt Res. 04812Miles Evaporators !"^$ %&s( Otay TES Sewage UNITED STA 0369Kilometers Imperial Disposal ÛA Tecate ¯ Beach Pond MEXICO Tijuana SOURCE: CalHydro 2006, 2007; NWI