4.2 Buena Vista Creek Watershed

Transcription

1 Buena Vista Creek Watershed 4.2 Buena Vista Creek Watershed Watershed Overview The Buena Vista Creek Watershed is the fourth-largest system within the Carlsbad Hydrologic Unit. The watershed extends approximately miles inland from the coast and totals 14,437 acres in area, comprising 11% of the Carlsbad Hydrologic Unit. Buena Vista Creek originates on the western slopes of the San Marcos Mountains (Photo 4.2-1) and discharges into the Pacific Ocean via Buena Vista Lagoon (Photo 4.2-2). Photo 4.2-1: Headwaters of Buena Vista Creek above the City of Vista Photo 4.2-2: Buena Vista Lagoon,

2 Carlsbad Watershed Management Plan Watershed Characteristics Geology The geology in the upper portion of the watershed is composed of Cretaceous granodiorites and Eocene marine rocks such as sandstone, siltstone, and mudstone. In the lower portion of the system, near the coast, the geology is composed of Pleistocene marine, marine terrace deposits, and Tertiary marine rocks, primarily sandstone and conglomerates. Soils Thirty-seven soil series have been identified within the watershed. These soil series are listed by family and mapped in Figure Many of these soil types are categorized as severely erodible soils (see Figure in the Carlsbad Hydrologic Unit Overview section). Significant sedimentation problems occur when these soils are exposed during seasons of high runoff. There is currently a significant sedimentation problem in Buena Vista Lagoon due to the effects of urbanization within the watershed and the lack of tidal flushing of the lagoon system. Hydrology As with the other watersheds within the Carlsbad Hydrologic Unit, there are no Photo 4.2-3: Floodwaters, City of Vista 1942 gauging stations on Buena Vista Creek, so little quantitative information on discharge rates and variation in surface flow are available for the system. Seasonal flows in Buena Vista Creek are typical of most coastal slope drainages in San Diego County, however, artesian springs provide for some surface flow even during the summer dry season. During wet winter weather or flood events (Photo 4.2-3) surface flow increases significantly. Natural surface flows are currently augmented by urban and agricultural runoff. Buena Vista Lagoon was originally a tidal system (Photo 4.2-4), however, during most summers the lagoon was closed to the sea. In 1940, a weir was constructed across the mouth of the lagoon, eliminating tidal flow. Because of this and other factors, Buena Vista Lagoon now functions as a freshwater lake with a fringing freshwater marsh. Photo 4.2-4: Buena Vista Lagoon,

3 Buena Vista Creek Watershed Figure 4.2-1: Soil series within the Buena Vista Creek watershed (SANDAG) 4-45

4 Carlsbad Watershed Management Plan Slopes Slopes within the watershed are generally low to moderate as shown in Figure At the eastern edge of the system, the slopes of the San Marcos Mountains are fairly steep and along the lower drainage, just inland from the lagoon, steep bluffs flank the floodplain in some areas. Toward the coast in the vicinity of Buena Vista Lagoon, slopes become very shallow. Watershed Form The Buena Vista Creek Watershed is long and relatively narrow in shape and is divided into two basins. The upper basin (4.22) is ovoid in shape and wider than the lower basin (4.21). Most of the tributaries of this system are confined to the upper basin with only one short tributary present in the lower basin as shown in Figure Drainage Pattern The Buena Vista Creek Watershed exhibits a simple drainage pattern as shown in Figure The main creek has four first order tributaries. Two first order tributaries, draining the west slope of the San Marcos Mountains, join to form the main stream of Buena Vista Creek, which continues as a second order stream until it terminates in Buena Vista Lagoon. However, even with its simple watershed form and drainage pattern, the Buena Vista Creek watershed still has a significant 100 year floodplain as shown in Figure and evidenced by the detention basin shown in Photo This scenario is likely caused by the fact that approximately 80% of the watershed is developed. Photo 4.2-5: Detention basin located at Brengle Terrace Park in the City of Vista. 4-46

5 Buena Vista Creek Watershed Figure 4.2-2: Slopes within the Buena Vista Creek watershed 4-47

6 Carlsbad Watershed Management Plan Figure 4.2-3: Buena Vista Creek landform, hydrology and floodplain information (SANDAG) 4-48

7 Beneficial Uses Designated beneficial uses within the Buena Vista Creek watershed are shown in Table Most of the agricultural uses are focused within the upper basin, many right at the base of the San Marcos mountains. As the tributary creeks make their way through the watershed, many of them are channelized to some degree or have had their drainage pattern altered by development, thus resulting in degraded and fragmented riparian corridors impacting the Warm, Wild, and Rare beneficial uses along Buena Vista Creek. Most of the recreational uses, including Rec-1 and Rec-2, are focused along the lower portions of Buena Vista Creek and around Buena Vista Lagoon, which is a heavily used bird watching location. The Buena Vista Audobon Society operates a nature Center at the eastern ed of the Lagoon. Buena Vista Creek Watershed Table 4.2-1: Beneficial uses within the Buena Vista Creek watershed (RWQCB, San Diego Basin Plan). Vegetation Communities Fourteen natural vegetation communities are present within the Buena Vista Creek watershed. Eleven other vegetation categories within the watershed consist of various types of disturbed habitats, nonnative vegetation, such as eucalyptus, nonnative grassland, and agriculture. Many of these have been combined for display purposes and are shown in Figure A complete listing of vegetation communities within the Buena Vista Creek watershed is included in Appendix B. Areas supporting natural vegetation are limited within the drainage and are dominated by chaparral and sage scrub stands on the western slopes of the San Marcos Mountains. Isolated patches of sage scrub are present in the uplands of the lower basin as well. There are also some fairly large stands of riparian vegetation, predominantly willows, present in the midsection of the lower basin (Photo 4.2-6). Stands of mixed cottonwoods and willows are also present in some areas along Buena Vista Creek. However, in general, riparian vegetation in this watershed is fragmented into isolated patches. Photo 4.2-6: Willow riparian in mid-section of lower basin, also shows lone tributary creek in the lower basin. 4-49

8 Carlsbad Watershed Management Plan 4-50 Some of the largest areas of freshwater marsh habitat in San Diego County are present around Buena Vista Lagoon as shown in Photo There are also scattered remnants of this vegetation type along the main stream of the drainage. Sedimentation could pose a long-term threat to the freshwater marsh and open water mosaic that currently exist at the Lagoon. Land Uses The vast majority of the watershed consists of an urban landscape, including developed parks and residential areas as well as a major regional shopping center and adjacent freeway / highway system. The high degree of development within the watershed has resulted in the channelization of large sections of Photo 4.2-7: Freshwater marsh around Buena Buena Vista Creek through the City of Vista (Photo 4.2- Vista Lagoon 8) to protect private property from flood damage. Interstate 5 traverses the western portion of the lower basin bisecting Buena Vista Lagoon, and State Highway 78 parallels Buena Vista Creek throughout the lower basin as shown in Figure On the flood plain of the lower basin there are small areas devoted to various agricultural pursuits and scattered orchards, predominately avocado, are present in the eastern portion of the upper basin (Photo 4.2-9). Photo 4.2-8: Flood control channel in Vista The pending Multiple Habitat Conservation Program (MHCP) will address conservation issues within the majority of the watershed. Several Biological Core and Linkage Areas are planned within the watershed as shown in Figure There are very few preserve areas identified within the Buena Vista Creek watershed. First, much of the Buena Vista watershed is already developed or in a degraded state. Second, a large percentage of the watershed is under private ownership, as shown in Figure 4.2-7, making it very difficult to acquire large tracts of land necessary to implement a larger more comprehensive preserve system. The preserve areas identified are planned to serve as permanent open space, which will be beneficial to water quality within the watershed. The eastern edge of the watershed is outside the boundary of the MHCP; conservation planning in this region will be addressed in the MSCP North County Photo 4.2-9: Avocado grove along drainage in headwaters of the watershed. Subarea Plan, which is still in the early planning stages. As

9 Buena Vista Creek Watershed Figure 4.2-4: Generalized vegetation within the Buena Vista Creek watershed (SANDAG 1995 Vegetation, KTU+A 2001) 4-51

10 Carlsbad Watershed Management Plan Figure 4.2-5: 1999 Generalized Land Use within the Buena Vista Creek watershed. (SANDAG) 4-52

11 Buena Vista Creek Watershed Figure 4.2-6: Habitat preserve system as part of the Multiple Habitat Conservation Program (MHCP- SANDAG) 4-53

12 Carlsbad Watershed Management Plan the North County Subarea Plan moves forward, efforts should be made to set aside significant areas of the headwaters of the watershed. Jurisdictional Environment The City of Vista occupies the majority of the upper basin (Photo ) and the western lower basin, while the San Marcos Mountains and portions of the southeastern corner of the upper basin are under the jurisdiction of San Diego County. In the lower basin of the watershed, the majority of the area north of State Route 78 is under the jurisdiction of the City of Oceanside; the southeastern corner of the city also extends south of State Route 78. In addition, the area south of the SR 78 is administered by the City of Carlsbad. These jurisdictional boundaries were shown previously in the Carlsbad Hydrologic Unit Overview section (Figure 4.0-2). Photo : Looking west over the City of Vista from the base of the San Marcos mountains The California Department of Fish and Game currently manages most of Buena Vista Lagoon as a State Ecological Reserve. Watershed Issues 303(d) Listed Issues The primary 303(d) issues within the watershed concern Buena Vista Lagoon and include excessive nutrients, coliform contamination and sedimentation. All three of these issues are directly related to urban runoff and stream channel modification that have occurred throughout the watershed. Feral duck populations within the lagoon area are another likely source of coliform contamination, possibly making it difficult to remove the impairment unless another criteria for impairments is chosen, or studies are completed documenting the relative contributions of wildlife versus human wastes to the coliform problem. This same issue likely applies to other waterbodies within the region as well. The high degree of urbanization within the watershed will likely prevent the system from ever acting as a natural system again, no matter how many restoration efforts are made. The focus at this point in time should be on the preservation of remaining open space lands and determining opportunities for water quality treatment projects. If the sedimentation of the lower portions of the watershed and lagoon are not slowed, then Buena Vista Lagoon will be in danger of becoming a large freshwater marsh with no open water mosaic, unless act dredging and management of the lagoon is imple-

13 Figure 4.2-7: 1995 Ownership within the Buena Vista Creek watershed (SANDAG). Buena Vista Creek Watershed 4-55

14 Carlsbad Watershed Management Plan mented. Obviously, it would be best not to let the situation worsen to that degree. Hydrologic Issues Efforts are underway to explore the possibility of opening up the lagoon mouth for increased tidal exchange. This effort needs to look at the advantages and disadvantages of this action since its implementation may have a profound effect on the local ecosystem that relies mostly on freshwater and brackish water conditions. Photo : Arundo mass just west of Warm Lands Ave in the upper portion of the watershed the watershed. Habitat Fragmentation Habitat fragmentation is generally extreme in the lower basin and most of the upper basin. However, there are several areas of habitat that are linked in varying degrees to larger habitat blocks outside 4-56 A fairly large area of nonnative grassland, juxtaposed to an area of high quality riparian woodland and disturbed wetland habitat is present in the lower basin where a small tributary enters the main stream. This area of habitat is linked along a narrow corridor to a large habitat block in the Agua Hedionda Creek Watershed. Both of these areas are identified as Biological Core and Linkage Areas in the MHCP. The eastern edge of the upper basin supports a fairly extensive track of natural vegetation on the western slopes of the San Marcos Mountains Invasive Exotic Species Invasive exotic species are a problem in the Buena Vista Creek watershed. However, species present in the watershed and detailed information about their abundance and distribution has not been well documented. Many of the species in Appendix B are probably present somewhere within the watershed. One species that is abundant throughout the mid and upper sections of the watershed is Arundo donax, which often occurs is contiguous masses of one acre or more along several of the drainages, as shown in Photos Photo : Arundo along drainage just north of Escondido Avenue and