«A thesis submitted to the faculty of San Francisco State University In partial fulfillment of The requirements for The degree Master of Arts In ...»
An archaeological study by R. J. Drake at the Sanchez Adobe site in 1950 found evidence that San Pedro Creek had meandered and overflowed its banks in the past (Drake 1951). When the adobe was built in 1842, the channel of San Pedro Creek was just a few feet below ground level; by 1950, the creek had incised a V-shaped channel down to 15 feet (Drake 1951). Drake hypothesized that the incision was due in part to agriculture and vegetation removal (Drake 1951).
After almost one hundred years of commercial agriculture in the San Pedro Creek Watershed, humans had transformed the landscape dramatically. The truck farmers aggressively altered the San Pedro Creek Watershed to maximize agricultural production. Areas were drained or irrigated as required, and sections of creeks were altered to facilitate the flow out of water out of the area. Flashboard dams placed across San Pedro Creek throughout this time to divert water to irrigation reservoirs also decreased the stability of the stream and increased the sediment load (Collins, Amato and Morton 2001). Large amounts of soil were left bare in the artichoke fields.
The intentional modifications to the watershed by the farmers also had unintended consequences. As Jeffrey Mount discusses in California Rivers and Streams (1995), agricultural practices affected California streams by increasing the area of exposed soil and altering channels, which led to increased erosion rates, channel incision, and sediment loads. Mount also notes that increased sediment in a creek and runoff from fields using manure degrade the quality of steelhead habitat (Mount 1995). In San Pedro Valley these impacts likely helped to fill in Lake Mathilde and the most of its surrounding
Kelsey McDonald - Thesis 54wetlands, as they were also being drained, and helped to degrade the steelhead habitat in San Pedro Creek.
Several of these changes in the watershed also unintentionally increased the potential for flooding in the valley. As Mount notes, large areas of exposed soil in the fields and reduced storage capacity for runoff decrease the lag time for the water to reach a stream channel, which during the heavy winter rains in California can lead to downstream flooding and creek bank erosion (Mount 1995). The railroad berm, and the railroad trestle and bridges built over San Pedro Creek also increased the flood hazard by constricting large flows, causing water to back up and spill over the creek banks.
Urbanization of San Pedro Valley: 1953-present Changes brought to the area by agriculture, including road access and drained, cleared land, provided a ripe opportunity for urbanization. As part of the post-World War II housing boom, starting in 1953 urban developers quickly transformed San Pedro Valley from an agricultural area to a suburban community (Map 13). Houses were built adjacent to the creek and in low-lying areas already likely to flood, and development increased the flood hazard in Linda Mar.
Andy Oddstad initiated the development in San Pedro Valley with his 3,000home Linda Mar development (Sharp Park 1953b; Hynding 1982). People were lured to the area by its natural aesthetics, including the hills and the ocean (Sharp Park Breakers
Kelsey McDonald - Thesis 551953a); however, within a few years these views had been altered. Houses were built up into and even on top of the hillsides of San Pedro Valley.
Development of the watershed also affected the creeks and their branches. In order to make way for development, Crespi Creek (now called Crespi Ditch) was culverted and channelized – the creek no longer appears on the 1956 USGS map (Map 13). Housing was built immediately adjacent to San Pedro Creek. Many of those owning homes adjacent to the creek would later have problems with erosion and bank failure, given the channel incision started earlier with agriculture and ranching. In addition, fill was placed on the northwestern part of the valley (Pampeyan 1994), presumably to allow building on top of any remnants of the wetlands and Lake Mathilde.
Homes built in the area of this fill north of Linda Mar Boulevard and east of Highway One lie below the creek and the high tide level, creating the need to pump runoff out of the area (Holmes 2003a). Because the pump stations and drains could not accommodate large amounts of water, such as that generated during winter storms in 1962, 1972, and 1982, the area was prone to flooding (Holmes 2003a).
By 1968 development extended even further up into the northeastern hills (USGS 1968). Developers had culverted the North Fork of San Pedro Creek and covered it with fill from the surrounding hills, in order to build housing on top (Azevedo and Azevedo 2002) - the North Fork no longer appears in most of the North Fork valley on the 1968 USGS map.
area of impermeable surfaces (roads, driveways, houses) significantly increases, and a new drainage system, including gutters and drainage pipes, is developed to remove water from the area quickly. Runoff enters the stream network more rapidly (i.e. has a decreased lag time), which not only leads to an increase in the amount of runoff, but also to an increase in the size of the flood peak (Mount 1995). More runoff and a greater flood peak increase the chances of overwhelming the downstream channels, leading to flooding.
Indeed, the San Pedro Creek Watershed began to experience flood problems related to its urbanization almost immediately after development of the Linda Mar neighborhood. Flooding in 1955 (USACE and City 1998a) and 1956 (SPFCC 1985, 3) was soon followed by major floods in 1962, 1972, and 1982. Despite the early flooding city staff allowed development to continue, even as city staff and a citizens committee looked into methods to reduce the flood hazard. Philip Williams & Associates, hydrology consultants, studied the flood hazard in San Pedro Valley, focusing on the 1982 flood, and determined that insufficient channel capacity was the primary cause of flooding in the area (Vandivere 1985). Some reaches of the creek were insufficient to contain greater than a 3-4-year flow, estimated at 600-1000 cubic feet per second (cfs) (17-28 cubic meters per second or m /s) (SPFCC 1985, 4; USACE and City 1998a, 9).
The areas with the least capacity, ranging from 600-2000 cfs (17-57 m3/s), started at the mouth of the creek at the ocean and went upstream to Peralta Road Bridge (USACE
Kelsey McDonald - Thesis 58and City 1998a, 10). A little further upstream the capacity of the Adobe Drive Bridge was also problematic – originally estimated at 500 cfs (14 m3/s) capacity (USACE and City 1998a, 10), this figure was later revised to accommodate up to a 15-year event (Holmes 2003a) or approximately 2,300 cfs capacity (65 m3/s) (USACE and City 1998a, 9). The 1982 flood, which caused over $5 million in damage, was only a 35-year event with a flow estimated at 2,900 cfs (82 m /s) (USACE 1989, 7). The flow of a 100-year event has been estimated as 3,500 cfs (99 m3/s) (USACE and City 1998a, 9).
Winter storms in February 1998 again caused San Pedro Creek to overflow its banks, flooding the Linda Mar Shopping Center, Linda Mar Boulevard, and Anza Drive, where floodwaters reached doorsteps (Larsen 1998a).
Human alteration of the San Pedro Creek Watershed together with its steep slopes and seasonally-heavy rainfall contributed to the development of a flood hazard in the northwestern area of San Pedro Valley. Farmers and livestock ranchers intentionally and unintentionally initiated many changes in the watershed that were accelerated by developers and homeowners, including increasing runoff and peak flows, and channel incision. Addressing the flood problem would require remediation of past alterations of the watershed.
Evaluating individual or micro-level response to a flood hazard as part of Palm’s integrative framework reveals that individuals influence and are influenced by elements at other levels. With each flood as awareness of the flood hazard increased among the new residents of Linda Mar, expectations originating at the cultural or macro level influenced their response. Likewise, residents influenced the response of elements at the meso level.
Traditional hazards research found that awareness or perception of a flood hazard increases after a flood event (to a greater degree after larger events) or when individuals see flooding as more probable. When residents first settle in a recently developed area, they lack understanding or awareness of a hazard (Burton, Kates, and White 1978). The higher the perception of a flood hazard the more likely an individual will act to attempt to reduce their risk. Although new to the area in the 1950s, Linda Mar residents (micro-level elements) quickly developed an awareness of the flood hazard in their area after repeated flooding and responded by asking the city (meso-level element) to control the problem.
The desire to control flooding is a cultural or macro-level element influencing hazard response. Federal policies toward flood control starting with the Flood Control Act of 1936 highlighted an antagonistic attitude toward flooding and a desire to control
Kelsey McDonald - Thesis 60it. The act called floods “destructive” and “a menace to national welfare,” and provided the federal government with the ability to “improve” waterways with flood problems (Legal Information Institute 2004a). As the early work in natural hazards identified, these policies led to an increase in the confidence of residents that flooding could be controlled. This confidence also led to the expectation that flooding should be controlled.
Another macro-level element is the question of who is responsible for addressing the flood hazard. In the United States the responsibility has usually pointed toward the individual (micro-level element); however, when damages are incurred individuals often push the blame off on others, such as government entities (meso-level elements), and threaten litigation against these entities (Palm 1990).
Flood of 1962 With the urbanization of San Pedro Valley in the early 1950s, a large number of people moved into the Linda Mar area. Unfamiliar with the area and any potential flood hazard, they soon found their awareness of the flood hazard increasing due to minor flooding in the 1950s. Not until 1962 did flooding cause great alarm. Winter storms in October 1962 brought large amounts of rain to the area, which led to major flooding in lower Linda Mar on October 13. The flooding covered 140 acres (USACE 1988, 3), extending from San Pedro Creek north-northeast into DeSolo Drive, Flores Drive, Montezuma Drive, Linda Mar Boulevard, Anza Drive and Arguello Boulevard, and out to
Kelsey McDonald - Thesis 61the Highway One (Map 4) (Pacifica Tribune 1962e; Pacifica Tribune 1962b). The worst flooding was in the northwestern section of the valley where a lake formed in the same general area Lake Mathilde formerly occupied, but that was now covered with homes (Pacifica Tribune 1962a). Two hundred people had to be evacuated from their homes, some in small boats due to the waist-deep water in areas, and 85 homes experienced major damages to their interiors (Pacifica Tribune 1962e; Pacifica Tribune 1972a).
Stores in the Linda Mar Shopping Center were also flooded by several inches of water (Pacifica Tribune 1962d, 1). Damages to homes and businesses reached between $500,000 (1972 price level) (USACE 1988, 3) and $1 million (Pacifica Tribune 1972a, 23).
With a heightened awareness of the flood hazard, the micro-level residents began influencing response at the meso level by calling on the city council (meso-level element) to provide explanations and to resolve the problem. Residents expressed their frustration with the city, whose staff had not yet started annual maintenance to clean out the creeks, for not having been better prepared (Pacifica Tribune 1962b). In addition to calling for increased maintenance in the creeks, the residents (micro-level elements) also requested that meso-level elements halt construction in the area until the flood problem was resolved (Pacifica Tribune 1962d, 8). Residents of Anza Drive further influenced the city council (meso-level element) by threatening legal action against the city and developers (meso-level elements) for their negligence in not cleaning the creek earlier and not completing drainage work respectively (Pacifica Tribune
Kelsey McDonald - Thesis 621962f). The residents wanted the problem solved in order to prevent future flood damage (Pacifica Tribune 1962f).
City staff (meso-level element) were initially defensive toward the residents.
City Engineer Al Roberts defended the city arguing that the creeks cannot be cleaned out too far in advance of winter storms or they just fill up with trash before the storms start, and that this storm came very early in the rainy season (Pacifica Tribune 1962f).
By late October, the meso-level response to pressure from the micro-level residents became more proactive. Mayor George Mason asked the city council to consider creating a citizens committee to look into the “drainage problem” (Pacifica Tribune 1962g), which it did in late 1962 or early 1963 (Pacifica Tribune 1963a). The citizens Drainage Committee proposed improvements to the drainage system and $2 million in bonds to finance them (Pacifica Tribune 1963a), but the city (likely the city council and/or city staff) did not obtain the necessary funding to go forward with the project.
The following year city staff also responded to the residents’ pressure by beginning work to clear out the stream channels and storm drains in September, more than a month earlier than in past years, as well as installing new drains in several sections of the city, including Linda Mar, and lining the stream channel near Capistrano (Pacifica Tribune 1963b). In the decade after the October 1962 flood, the Department of Public Works also improved the existing pumping stations and built a new station to accommodate larger flows (Pacifica Tribune 1972b; Barnard 1982b).
cause them to act by calling on meso-level elements to respond to the flood hazard (Figure 2). The meso-level elements, including the city council and city staff, eventually responded by creating a citizens committee and making some drainage improvements.