Background - (Original Page No. 22)

The Beach

The Del Mar beach parallels the City along its western edge and is the most heavily used natural resource within the community. There is a tendency to believe that this resource has always been here and will remain forever virtually unchanged. Unfortunately, this assumption is not completely correct.

The supply of sediment to the City's beaches has been reduced since the 1930's for several reasons: 1) inland dams which have prevented sediments from traveling downstream; 2) construction of structures which hamper the movement of sand parallel to the coast; 3) weather conditions, as of 1975 in an unusually dry cycle, which have reduced the flow of sediment to the ocean from rivers and streams; and 4) the settlement of sediment flowing down the San Dieguito River into the San Dieguito Lagoon.

According to recent surveys contracted partially by the City, the Del Mar beach has lost a large amount of sand in recent years. It appears that if the existing sand depletion rate continues, Del Mar will have a rocky winter beach by 1980 or 1985, and a year-round rocky beach by perhaps 1995. In addition to minimizing beach use, this depletion process will increase the exposure of sea cliffs and beachfront structures in Del Mar to winter storm waves.

According to reports prepared for the San Diego Regional Coastal Commission, the elevation of the beach dropped three feet between 1964 and 1973, an annual loss of four inches. The Del Mar barrier beach is at a ten foot elevation. During the winter, a seven-foot tide with a six to seven-foot surf behind it (not uncommon) would inundate beachfront homes. In 1972, 1973 and 1974, the City built a six-foot sand berm along the western edge of the property lines of the beachfront homes in order to provide needed protection. The berm was successful in protecting the structures and was generally washed out by the end of the winter due to high tides combined with storm waves.

One other less significant condition affecting the Del Mar beach is the encroachment of private decks and patios of north-end residences onto the public beach. This activity has reduced the amount of beach width available to the public and could pose a future problem as a rocky beach becomes more predominant and the width of the sand beach is reduced and shifted eastward.

San Dieguito Lagoon

The lagoon formed by the culmination of the San Dieguito River is generally bounded on the north by the Del Mar Racetrack, Fairgrounds and parking lot; on the south by some light industrial development and San Dieguito Drive; and on the east by Interstate 5. The western half of the lagoon lies in the City of Del Mar and the eastern portion is in the City of San Diego. About two-thirds of the former extent of the San Dieguito Lagoon was filled during the development of the Del Mar Racetrack and Fairgrounds.

The lagoon was tidal until the early 1940's and, since that date, has been closed off to the ocean by a sand barrier. This barrier was constructed and maintained to prevent lagoon water, the source of which was secondarily treated effluent pumped into the lagoon by the City of Del Mar, from polluting the adjacent beach. In 1974, Del Mar's effluent discharge into the San Dieguito Lagoon was diverted into the San Dieguito Metropolitan Sewerage System. It is clear that this elimination of a water source will result in a gradual drying out of the lagoon unless alternative sources are devised.

The western portion of the lagoon comprises a shallow saline pond. The shallow lagoon and its inland channels are inundated to a depth of a few feet by trapped tidal water. The water grades in salinity from almost seawater in the west to slightly brackish in the east.

The overflow of treated sewage effluent into the impounded waters of the lagoon has long created serious eutrophication and mosquito control problems and has been the cause of odorous conditions. Although these conditions should be alleviated by the diversion of the effluent, eutrophication problems are likely to persist.

Over most of the past 15 years, there has been no surface flow of fresh water other than minor storm runoff in the lower San Dieguito River. Because of the lowered ground water table in the lower valley, saline ground water is moving inland and well water quality for three miles upstream has become seriously degraded.

San Dieguito Floodplain

Coastal San Diego County is subject to sudden and severe floods. The County's streams generally have steep side slopes near their origin, but for the remainder of their courses to the Pacific Ocean, the stream channels flatten out as they pass through wider canyons and cross broad valleys. These flatter channels have insufficient capacity to carry large volumes of water, with the result that the streams overflow their banks and inundate the valley plains.

Many years of subnormal rainfall have created an apathetic attitude toward the danger of floods. Residential, commercial, and industrial developments are spreading over flood plains that are subject to inundation. This peril is not imagined danger. The largest flood in recent times in San Diego County occurred in 1916. This flood, by far the most destructive on record, caused 23 drownings in San Diego County. The extensive damage attributed to this and other floods in 1927 and 1938 is insignificant in comparison to the damage that would result today were there to be another flood of the magnitude of the one that occurred in 1916.

This danger also exists in Del Mar. The San Dieguito River, because its outlet is so wide and flat, has overflowed its banks several times in the past. The effective drainage basin of the San Dieguito River has been reduced by the construction of three dams (Hodges, Poway, and Sutherland). Although these dams do offer some protection from normal annual runoff, they are not intended nor designed as flood control structures and offer no protection from runoff equal to the great historic floods of the past.

According to reports of the State Department of Water Resources, the San Dieguito River flood plain is subject to a serious 50 and 10-year potential. Therefore, it can be seen that flooding is a future certainty.

Flood-prone areas are defined under two separate categories: floodway and floodfringe. These two categories together comprise the flood plain. The floodway is the area within which flood waters would flow during a 100-year flood or on the other hand, be subject to more frequent flooding in the event that existing flood control facilities upstream were destroyed. Structures within this area should be prohibited in order to allow a free flow of flood water. The flood-fringe, on the other hand, is that area in which flood waters would spread out, inundate the land, lose their momentum, be stored and then be dissipated. Structures in flood-fringe areas should be protected or controlled to assure that they would be unharmed by flood waters.

Del Mar's San Dieguito River flood-fringe extends over a variety of developed and undeveloped land in four general areas:

Northeast Quadrant - North of the floodway and east of the railroad. This area includes the Del Mar Racetrack and Fairgrounds and accompanying parking areas.

Northwest Quadrant - North of the floodway and west of the railroad. This area is undeveloped, and some of it is annually inundated with water.

Southeast Quadrant - South of the floodway and east of the railroad. This area includes the City's public works yard, commercial uses, and undeveloped land.

Southwest Quadrant - South of the floodway and west of the railroad. This area is nearly completely developed with single and multiple family residential development.

Vegetation

Del Mar falls within the Coastal Scrub Plant community and, other than portions of the San Dieguito Lagoon, has been extensively modified by development. Existing tree masses provide vegetative elements that add to, as well as help to define, the character of the City. Some of the most dominant trees include: 1) the Monterey Cypress, a native plant from Carmel Bay, California that has been used extensively throught Del Mar; 2) the Torrey Pine, a species native to the bluffs at Del Mar and, like the Monterey Cypress, used throughout the City as an ornamental plant; and 3) the Eucalyptus, an ornamental tree imported to this country from Australia.

Bluffs

Del Mar is characterized by a number of sandstone bluffs throughout its boundaries. The larger and more prominent bluffs are adjacent to the beach and at the south end of the community. In addition, however, there are numerous small bluffs which are worth consideration for protection as natural features throughout the Del Mar hill area.

These bluffs serve as unique land forms providing visual relief and diversity within Del Mar. Efforts should be made to preserve these features intact where-ever possible but, particularly, at the north and south ends of the hill areas of the community.

Steep Slopes

The steep slopes indicated in this Plan are defined as having a slope of 25 percent grade or more. These are the areas central to the problems of erosion. This is particularly true in those areas where the natural vegetation and ground cover are not thick. In the six months between October and March, the total precipitation averages 9.5 inches along the San Diego coast. Perhaps more important are the rainfall intensities expected, on the average, once in 50 years. For the coastal area, the rainfall in a 24-hour period during such a 50-year storm is 4.5 inches. This intense rainfall would create problems of erosion, mudslide and mudflow which are compounded by development.

Aside from these public safety considerations, steep slopes can give a greater impression of openness than the area alone would indicate if left undeveloped. In essence, such land can give a sense of place by physically defining and separating neighborhoods and communities from one another.

Efforts should be made to preserve these features intact wherever possible, but particularly at the north, northeast and south ends of the hill areas of the community.

Seismic Hazards

Ground Breaking Potential - Ground breaking results from a surface rupture of a fault. A fault is a fracture in bedrock which may extend upward to the ground surface and along which there has been displacement of the two sides relative to one another.

Only two faults are known or inferred from areas within Del Mar. Both are relatively short and neither one is known to be active. Their locations do not coincide with any known earthquake epicenters. The last movement on the fault near the railroad overpass at the south end of the City was believed to have taken place more than 50,000 years ago. The age of the other fault has not been investigated.

There are seven other faults (or inferred faults) located within two to three miles of Del Mar. Of these, movements known to have taken place within the last three million years have occurred on only the Carmel Valley and Rose Canyon faults. Movements along the Rose Canyon fault are believed to have taken place in the last .5 million years. For this reason, because it may be part of a very long and active fault zone, and because of the known occurrence of earthquake epicenters along its trace, this fault could constitute a potential threat to Del Mar. However, the fault need not be considered a serious danger to residential construction until more evidence becomes available concerning its length and activity.

Ground Failure Potential - Ground failure can occur due to lateral spreading, earth lurching, landslides, and differential settlement.

Within Del Mar those areas having the greatest potential of ground failure include: 1) all of the sea cliffs bordering the City of Del Mar; 2) areas of the Del Mar Formation of Torrey Sandstone in which existing slopes exceed 25 percent; 3) all areas having a slope of 10 percent or more where the strata has been substantially tilted in the direction of the slope. (The determination of (3) above will require detailed field mapping); and 4) the terrace escarpments made up of colluvium and slope wash in Crest Canyon and on the northeast side of the Del Mar Hills.

Liquefaction Potential - Liquefaction is a common occurrence during earthquakes in areas that have high water tables and silty or sandy soils. During the earthquake, the vibrations can cause a deterioration of the friction between the wet soil particles. In severe cases, a condition similar to quicksand can result in an area which was previously thought to have stable ground.

Within Del Mar, the San Dieguito Valley and Lagoon has significant liquefaction potential due to the deposits of alluvium and slope wash in this area believed to be covering a mixture of beach sand, bay sand and salt, and alluvial sediments (largely dry and silt) which may be mixed with occasional salt and dry marsh deposits.

Tsunami Potential - Tsunamis, also known as tidal waves, are seismic in origin, usually caused by an underwater seismic disturbance or, less commonly, large submarine landslides. Although such waves appear to be only one or two feet high in the open ocean, they increase in height significantly as they approach the coast.

Although the probability of a Tsunami occurrence is not great, a large Tsunami striking this area could result in great loss of life and property.

Areas that are especially prone to Tsunami hazards include low flat areas such as the San Dieguito Valley and the low lying beach areas in the northern part of the City. Tsunamis can also do damage to areas that have steep cliffs which are exposed to sea waves by seriously eroding the cliffs, increasing landslide potential, and endangering any structures built near the cliffs.

Archeological Sites

Several archeological sites exist within Del Mar according to the San Diego Museum of Man. Because vandalism may occur on these sites, information about their specific location should remain confidential except where owners of property containing such sites must be involved in their preservation. It can be said, however, that the following general areas contain one or more sites:

1.

North bluff area west of Camino del Mar.

2.

In the vicinity of Turf Road and Via de la Valle.

3.

On the north slopes of the Del Mar hills above Jimmy Durante Boulevard.

4.

On the northeast slopes of the Del Mar hills above San Dieguito Drive.

5.

Torrey Pines Terrace area.

6.

Del Mar Canyon area.

Air Quality

Air pollution is the inclusive term used to describe the smoke, dust, fumes, vapors, gases, ash and other waste products that collect in the air as a result of human or natural activities. Normally, the air pollutants are carried away by wind currents and dispersed into the atmosphere. However, when there is a temperature inversion, a ceiling of warm air forming above the cooler and heavier air near the ground, these pollutants are effectively trapped. They then may undergo a photochemical reaction triggered by the sun's rays, and thereby produce the phenomenon popularly referred to as "smog".

It has been estimated that 2500 tons of pollutants are dumped into the atmosphere from San Diego County daily. About 75 percent of this pollution comes from automobiles, with the remainder generated by industrial and commercial operations, open burning, and various other activities. California and the federal government have respectively set .10 and .08 parts of pollutants per million parts of air for one hour as the standard index of adverse air pollution. These standards are exceeded on many days of the year in San Diego, most often in the summer and fall. Environmental Protection Agency studies have characterized the San Diego Region as having the highest urban air pollution potential in the nation.

The San Diego Air Pollution Control District has monitored air quality rather comprehensively since 1972. It is evident from their data that 1974 air pollution (oxidants) in San Diego exceeded State and federal standards on approximately nine days.

The micro-meteorology of the Del Mar area is characterized by brisk sea breezes during the day and weak drawing winds at night and early morning. Inversions and stable conditions are common at night and early morning with the sea breeze becoming established at approximately 9 a.m.

The lack of existing or proposed potentially polluting industrial activities within or directly adjacent to the community results in the probability that the greatest internal threat to air quality in Del Mar would appear to be vehicular emissions. In order to accurately determine changes in air quality, efforts would have to be made to establish a monitoring location within the community.

Open Space

Five major open space areas existed within the community as of 1974. They encompass a diversity of topography along nearly all City boundaries, thereby, serving to buffer and identify Del Mar as a unique and distinctly separate community.

1.

The San Dieguito Lagoon and Floodway . This area includes lagoons, marshes, grassland and the racetrack with associated parking areas. Federal, State and local laws exist and have application to the use of land in the flood plain. The Comprehensive Planning Organization has declared the area as a natural resource of regional significance in need of both preservation from development and restoration as a natural wetland area.

2.

The beaches, bluffs and accompanying canyons along the ocean . This area provides access and exceptional vistas, and possesses unique geological formations. The future of this area is threatened by sand depletion and landslides.

3.

The bluffs and canyons at the south end of the community . This area provides a very interesting combination of high bluffs with extensive vistas, deep cuts through the sandstone cliffs and rugged canyons with native vegetation, including Torrey Pines.

4.

Crest Canyon . This area falls primarily within the political jurisdiction of the City of San Diego, however, portions of the eastern slopes are within Del Mar. This canyon has been declared to be of regional significance by the Comprehensive Planning Organization.

5.

Bluffs and slopes along the north and northeast edges of the Del Mar hills . This area contains a variety of views and topographic features including bluffs and steep slopes and serves as a northern open space buffer for Del Mar.

A limited supply of open space parcels within existing developed areas still exist. Some of these parcels possess unique natural characteristics or potential as recreational areas. These primary and secondary sites are indicated on large scale maps available with the City of Del Mar.

The City of Del Mar presently provides the public with two open space areas.

Seagrove Park is located at the foot of 15th Street overlooking the ocean. This one-acre park was completed in 1974 and includes benches, trees and a large turfed area.

The Del Mar Bluff Preserve is located north of the mouth of the San Dieguito Lagoon adjacent to the ocean. This four-and-one-half-acre promontory possesses views of the coastline and the City of Del Mar to the south, and the Pacific Ocean to the west.