Flooding: brought to you by the City of San Diego

A telling history of a north county watershed

by Mike Kelly


The Peñasquitos watershed is one of the few remaining, relatively undisturbed natural habitats in North County. As with any undeveloped area in the midst of rampant urbanization, it is under constant, direct and indirect pressures from local development. Fortunately, this area has a champion The Friends of Peñasquitos Canyon, a local non-profit organization dedicated to its preservation. Mike Kelly, president of the group, gives us a unique expert's view of the history of the area, and of the impacts of development around and directly in its flood plain.

isit the junction of Peñasquitos and Sorrento Creeks in Sorrento Valley these days and you'll probably be appalled at what you see. Both have been bulldozed. Sorrento Creek has been bulldozed into a channel 100 feet wide and over 5 feet deep for a distance of 1,000 feet to the edge of Torrey Pines State Reserve. The bulldozing of Peñasquitos Creek has just begun, but will eventually extend from its junction with Sorrento Creek all the way to I-5, again, some 1000 feet x 100 feet by five feet. A new channel is being bulldozed in each creek to alleviate flooding of the Sorrento West Business Park.

If you want to see this marvel of modern engineering for yourself, go to the north end of Roselle Street in Sorrento Valley. Park and walk behind the buildings on the east side of the street. You'll see sandbags, the dike and the new channel. If you work your way from the north end of these buildings to the south, you'll eventually come to a new pond at the intersection of the two creeks. Looking east you'll be seeing Peñasquitos Creek as it hits Sorrento Creek. Coming in from your south will be Carroll Creek.

Besides detailing the what's-and-why-for's of this, our concerns and actions, I also want to put this in the context of Peñasquitos Lagoon and its watershed. The Peñasquitos drainage is the biggest part of this watershed. Along the way, I'll provide a brief and I think, surprising history of our creek.


Ridiculous flooding


The Sorrento West Business Park runs between Roselle Street, I-5, Flintkote and Estuary Way. The older parts were built out in the 1960s. Occupants are primarily a collection of hi-tech companies in leased buildings. This district flooded September 1997, January 1997 and November 1996.

Remember the famous floods of September of '97? Probably not there weren't any in the rest of the city. However, less than 1 inch of rain caused Roselle Street to flood with two feet of water, stranding motorists who had to be rescued from their trapped vehicles.

This event is called a 1-year rain event, since this is the amount of rain you would expect every year. In 1995, rains equivalent to a 10-year event (an event expected to occur an average of once every 10 years - you get the idea) considered a moderate rain event caused serious flooding in the interiors of buildings. The resulting damage cost flooded businesses millions of dollars. One company went out of business and is suing the City for not preventing the flooding.

Rail transportation was halted through the area because of the flooding. Auto traffic had to be rerouted from one of the busiest intersections in the city. The railroad tracks are often under water during the bigger events, requiring a railroad person to walk in front of the trains to be sure the bridges over the creek are still there!

Flooding during light rain events such as those of this past year is ridiculous. Why is it happening? Four factors are at cause: bad land use decisions, urbanization of the watershed, channelization, and lack of maintenance. All contribute to the history of flooding in this area.


Problem #1: Flood plain development


To put it simply, the Sorrento West Business Park was built in a flood plain. Poor land use decisions by the City of San Diego allowed building in this flood plain (and others, such as the Tijuana River Valley).

Legally, the City justifies permitting this building by saying that these flood plains weren't officially mapped by the Army Corps of Engineers (ACOE) or the Federal Emergency Management Agency. This is technically true: the ACOE didn't officially map the area until 1967. The maps show the "intermediate regional flood" (100-year flood) and the "lesser flood" (50-year flood) areas for Soledad Canyon, Carmel Valley, Los Peñasquitos Creek, Poway Creek, Rattlesnake Creek, and Pomerado Valley, the watershed of Los Peñasquitos Lagoon.

Truly, determining the extent of the flood plain can sometimes be difficult. However, this is not the case in Sorrento Valley. City planners had to know they were permitting development in a flood-prone plain. After publication of the ACOE report, some of the future developments were required to build on higher pads, theoretically lifting them out of the flood plain. However, the streets surrounding them were still below flood plain level, leaving buildings surrounded by floodwaters .

Even back in 1967, ACOE noted that floodwaters overtop the channels and cause damage to residential and commercial development or to property suitable for such development. "The existing flood-control works in Los Peñasquitos area are inadequate for large flows." The report noted that these conditions existed for all six of the creeks they studied in the drainage area.


Problem #2: Urbanization


The ACOE report was prompted by a request from the City of San Diego, as planners looked at the plans for future development, i.e., urbanization of the watershed. Ironically, in 1967, it was the City of Poway that was undergoing the rapid development, while development in Mira Mesa and Carmel Valley was still a gleam in developers' eyes.

Urbanization has a big impact on a watershed. As you convert natural lands or agricultural lands to rooftops, parking lots and streets (impervious surfaces), you reduce the capacity of a watershed to absorb water. The resulting runoff is carried via storm drains into our canyons not into our sewer system and safely out to the ocean as many people assume. As urbanization progresses, the water flow into the canyons far exceeds historic levels.

One impact is an increase in peak flood flows. Prestegaard estimated that the 2-year flood volume would double on major streams, and increase by four times on urbanized tributary streams. Similarly, a 100-year flood volume would increase by 1.3 times on major streams and by 3 times on tributaries (Prestegaard 1975). In the same report, Prestegaard studied the channels throughout the watershed and stated unequivocally that, "The channel in Soledad Valley [the old name for Sorrento Valley] cannot contain any but the lowest flows."

A 1992 San Diego Association of Governments (SANDAG) report came to similar conclusions. This report also predicted that the Sorrento Creek channelization could carry only a 15-year flood peak event with urban development in place. Other impacts expected from urbanization in our drainage have been well studied and include: increased erosion (especially during the construction phase), increased sediment load and declining water quality due to pollution in urban runoff pollution.


Problem #3: Channelization


So, we not only have buildings directly in the flood plain throughout all of the creeks in the watershed, but we also have large-scale urbanization that increases the volume and frequency of flooding. Historically, the reaction to this threat has been to dam, dike and channelize our rivers and streams, whether a flow is as large as the Mississippi or as small as Peñasquitos Creek and its tributaries. All of this has been done to these creeks.

The idea is to take the natural stream beds and deepen them, widen them and, often, line them with concrete or rip rap (large rocks). Sometimes, the entire stream bed is put inside a culvert to carry the water out to the ocean fast. This works in many cases if you build it big enough for your biggest flood event, maintain the dikes or channel walls, and keep them clean of debris, silt and vegetation. Ironically, such channelization is often done on a piecemeal basis, as is the case in our drainage.

Many of the tributaries in the City of Poway that feed Peñasquitos Creek are channelized. This sends more water downstream faster, increasing peak flows and the tendency to flood! It's a way of exporting your flooding problem downstream. (A San Diego city engineer recently complained in a meeting I attended that it was impossible to get the City of Poway to return calls on this subject.)


Problem #4: Maintenance


Our fourth and last factor is the lack of maintenance. As with many other things in our city (e.g., sewers, roads), maintenance of channels is often the first thing to be cut in the City budget, deferred to the "future." The result is crisis management. The channels approaching and in Sorrento Valley were inadequately maintained for decades. Silt carried by the increased erosion due to urbanization in the watershed built up to a depth of 12 feet in some areas. This new land was colonized by native and exotic plants such as arundo donax (giant reed). The latter is well-known for clogging channels. The buildup of vegetation, in turn, traps more sediment and slows down flood waters just where they were meant to pass quickly. Flooding increases.

The lack of maintenance also meant that storm drains from Roselle Street that emptied into Sorrento Creek were blocked by the silt buildup. The result: flooding in light to moderate rain events. The water in Sorrento Valley literally had no place to go and created a lake during each moderate rainfall.


Environmental concerns


The Friends of Peñasquitos Canyon have two sets of concerns connected to this flooding and attempts to correct it. First, the only wildlife corridor connection from Torrey Pines State Park to the outside natural world in this case, Peñasquitos Canyon Preserve is along Peñasquitos Creek, from its junction with Sorrento Creek upstream under the I-5/I-805 merge. This connection is vital for the biological health of the wildlife in both parks. Bulldozing these creeks will adversely impact this connection.

In meetings with other environmental groups (Audubon, Surfrider), Sorrento West businesses, State Parks and City Engineering, the Friends pushed to save the wildlife corridor connection by reducing the proposed bulldozing. Originally, the City proposed a new pilot channel to the ocean that would be 200 feet wide in Sorrento Valley. This would have destroyed the wildlife linkage. Facing stiff opposition from many quarters, the City brought forward a new plan calling for a 100-foot-wide channel in Sorrento Creek. This new plan leaves an adequate, heavily vegetated corridor along the natural creek to the east.

It's my opinion, shared by the Friend's Tracking Team/Wildlife Survey leader and a wildlife biologist who just completed a study for the State Park, that the bulldozing of the bottom of Peñasquitos Creek, lowering the silt level and reducing the cattail density, can actually improve wildlife movement through that portion of the creek. Currently, the high silt and vegetation buildup, especially the arundo donax, blocks wildlife movement in the area. The key is maintaining brush cover on the two banks for the wildlife.

Second, we are concerned with the impacts of urbanization in both Parks. Erosion is a serious problem in Peñasquitos Canyon, threatening already endangered plants (monardella linoides viminea) and wiping out all vegetation in portions of drainages (especially López Canyon). Increased flows and erosion are causing accelerated incising of the creek, with headward erosion and dewatering of the associated wetlands.

Erosion also means too much silt gets carried downstream where it clogs the channels, as well as causing a buildup in Peñasquitos Lagoon, creating upland habitat in place of saltwater marsh. Runoff pollution from development ringing the Preserve reduces our water quality to "fair" in water quality testing the Friends and various agencies have conducted. For instance, too many nutrients and too much nitrogen and phosphorus in the water promotes a buildup of algae and "algal blooms," to the detriment of fish and benthic organisms.

This situation is exacerbated by the inadequate tidal flushing in the lagoon, due to the closing of the mouth of the lagoon by various highways and bridges crossing it. With the mouth closed and too many nutrients and consequent algal blooms the lagoon can quickly deplete its oxygen, leading to kill-offs of its fish and mollusk populations. This, in turn, effects the bird populations that depend on the lagoon for their food.

Urbanization also means more fresh water all year, as well as during storm events, leading to a buildup of freshwater habitat at the expense of salt marsh in Peñasquitos Lagoon. Salt marsh habitat is rarer and is a priority for preservation.


A brief history: a creek by any other name ...


Sorrento Valley and Sorrento Creek are new names. Until the 1960s, they were Soledad Valley and Soledad Creek. There is still a Soledad Canyon in the southern (upper) portion of Sorrento Valley. It is now only a major finger canyon, running northwest to southeast off Carroll Canyon, carrying the Santa Fe Railroad under Miramar Road and across the Marine Air Station. (It's a beautiful canyon, with some of San Diego's oldest coast live oaks, good habitat, mule deer, hawks, etc. It's also a good wildlife corridor. You can access it off of Carroll Road at Scranton.)

Peñasquitos Creek once referred to the entire length of the creek, from the foothills of Poway all the way into Soledad Valley. Now, the upper portion in Poway is called Poway Creek.




Webster's defines "watershed" as "the area drained by a river or river system." The watershed that drains into Peñasquitos Lagoon ranges from 95 sq. mi. (ACOE, 1967) to 98 sq. mi. (Prestegaard 1975), depending on whose estimate you use. It includes the drainages of Carmel Valley, Carroll Canyon and Los Peñasquitos Canyon (Peñasquitos Canyon reaches all the way up into Poway).

The Peñasquitos drainage or sub-watershed is the largest of the three, being about 58 sq. mi. The major creeks or tributaries flowing in these drainages include Deer Canyon Creek, which flows into Carmel Creek in Carmel Valley; Carroll Creek; and Pomerado, Rattlesnake, and Beeler Creeks which all flow into Poway Creek, which becomes Peñasquitos Creek.


The insults begin


I use insults here as both a technical term for negative impacts on the land and water, and as a pejorative.

The first major insult to Peñasquitos Lagoon occurred with the building of the railroad in about 1888. This began the process of closing the lagoon mouth to the influence of the tides that are necessary to maintain it as a healthy salt water-dominated water and marsh habitat.

Ellis and Lee reported in 1919 that the "Soledad Streams" were able to keep narrow channels open through the beach, at least during part of the year. However, the building of Highway 101 across the lagoon in 1932 worsened the situation. The lagoon began to be closed most of the time, causing a die-off of saltwater-dependent organisms and vegetation and a shift in the types of vegetation present. For example, no living mollusk species were found in several studies in the 1960s. Only during exceptionally wet winters could sufficient freshwater collect to break through the barrier bar that develops in the lagoon mouth.


Sewage flows in creek and lagoon


In the 1980s, our daily paper often treated us to news of sewage spills from the infamous pump station in Peñasquitos Lagoon, closing beaches and promoting organism die-offs. However, what most people don't know is that treated sewage (the PR term is "treated effluent") was intentionally pumped into the Lagoon for decades.

The Callan Treatment plant, an old WWII facility located on Torrey Pines Mesa, was reactivated in the 1950s and began pumping 50,000 gallons of treated effluent per day into Soledad Creek and the lagoon. It was joined in 1962 by the Sorrento plant, which was pumping about 500,000 gallons per day into the same lagoon. Another facility, the Pomerado Waste Water Treatment Plant, pumped even more treated sewage into Peñasquitos Creek from 1962 to 1972.

In addition, the Peñasquitos Settling Ponds were used for sewage treatment, perhaps as late as 1967; I have yet to find a good report on these. These ponds may still be seen, vegetated now, just west of the Rancho Santa Maria ranch house off Black Mountain Road. These 14 acres of dikes and ponds sit right next to Peñasquitos Creek. What we don't yet know is if any of this effluent was pumped or leaked into the creek. (This is an area the Friends hope to restore soon.) Many folks living downstream during this period, in Mira Mesa and Rancho Peñasquitos, had no idea the stream they were visiting and their kids were playing in was in large part treated sewage!

Plans for an SDGE Nuclear Power Plant in Sorrento Valley and for a new Pomerado Water Reclamation Plant with live stream discharge were both discarded. Public opposition played a big role in both decisions.


"Effluent" impacts on lagoon


The discharge of treated effluent brought two problems with it. One was fresh water flows into the lagoon that were way above the historic levels, particularly outside of the rainy season. This effluent flow occurred during a time when urbanization was also adding fresh water to the system, not just during storm events, but all year long due to irrigation.

The second problem was the high nitrate and phosphate levels of the effluent. This combination of additional nutrient-rich fresh water pouring into a closed lagoon system without adequate tidal flushing led to repeated die-offs and the shift in vegetation types. Elevated temperatures occur up in the waters of a closed system like this, and contribute to the die-offs. Such a die-off occurred in San Elijo Lagoon in the summer of 1997.

Another problem caused by this infusion of effluent was a tremendous mosquito problem. This prompted significant public opposition to these flows and, combined with studies of the negative biological impacts, led the Regional Water Quality Control Board to oppose continuation of these existing facilities or the building of new ones.

Peñasquitos Lagoon's mouth is now kept open with periodic and expensive bulldozing but it accomplishes its purpose of permitting tidal flushing.


Impacts on Peñasquitos Creek


Peñasquitos Creek is now a perennial creek, flowing year round. Was this always the case? Firsthand observations by various individuals, plus U.S. Geological Survey data for the creek starting in 1964, indicate that the creek wasn't consistently perennial. In years with above average rainfalls, heavy late seasonal rainfalls or significant summer rain, the creek flowed to the lagoon throughout the year. During years of average to low rain flows, certainly during periods of extended drought, it was seasonal. This shouldn't be surprising in our arid climate.

The flow data we do have (on the web at www.usgs.gov) illustrates the impact of the live stream discharge between 1962-1972. From 1965-1972, the median discharge of treated effluent was .90 cfs (cubic feet per second), ranging from a low of .03 cfs to a high of 3.50 cfs. It also showed a sharp drop when the plant closed in 1972. From 1973-1979, the median discharge dropped to a low of 0.10 cfs, with a range of 0.00 to 25 cfs. In other words, at times, there was no measurable flow in the creek. Thereafter, the median discharge steadily increased, even during the summer months, probably reflecting increased runoff due to urbanization in the watershed.

The natural springs feeding Peñasquitos Creek are too few and far between to promote a year round flow, except in their immediate downstream areas. The largest natural spring pumps up to 86,000 gallons per day into the creek. If you were standing downstream of one of these springs, the creek would certainly be flowing past you at any given time, probably, but not all the way to the ocean. If you were standing downstream in the lagoon during the period of 1950-1972, you would have been seeing a flow but mostly of treated effluent.

Now, however, we have a strong year-round flow, even during the most recent drought, due to irrigation, car washing, etc.. Is this additional flow good or bad? These flows do tend to bring toxics (oil from driveways), pesticides and fertilizer all harmful to some extent to the water and the organisms in it. However, each significant finger canyon in the Preserve now has a new riparian area in it: this is both good and bad. Riparian areas in the desert tend to be scarce, but extremely important to wildlife. Adding some small acreages is beneficial. On the negative side, this same runoff brings seeds of exotic plants, which tend to have a negative impact on local flora and fauna. The Friends are spending considerable energies clearing these exotics out of these same canyons. Constant management can control the exotics.

The worst impact from urbanization, I feel, is the increase in peak flow and velocity during storms. We are seeing much more erosion, areas that are denuded and remain so, and beds of cobble or bedrock with no vegetation. The Friends are still grappling with how to mitigate this problem.



  When their projects impact salt marsh and fresh water riparian areas, the City is required to mitigate by restoring or creating similar habitat elsewhere. As mitigation for the creek bulldozing, a proposal to remove old dikes, restoring the historic flood plain, was accepted, and restoring wetlands was tentatively accepted. This is the area we call the "bean fields," north and east of the El Cuervo adobe ruins at the Sorrento Valley end of the Preserve. Detailed analysis and plans are being worked up. We wanted this proposal to emphasize the need for upstream solutions - where the problems originate - and solutions that deal with the underlying causes of the flooding and the negative impacts on the lagoon.


City stonewalling

In the meetings with the City Engineering Dept., The Friends and others emphasized the importance of looking at the flooding and other problems we have identified as watershed problems. We argued for upstream solutions to reduce the siltation and peak flows that cause downstream problems. We argued that this would be safer and cheaper for the taxpayers in the long run, in place of the crisis management of the past.

Unfortunately, we did not feel that the City was responsive to this perspective, in any way. We will keep pushing this perspective. It's the right thing to do.

Reprinted from Canyon News, the newsletter of the Friends of Los Peñasquitos Canyon Preserve, Inc., with permission. To find out about memberships, call (619) 484-3219 or (619) 566-6489. To find out about volunteering to help with their ongoing preservation and restoration projects, call 619) 224-4192.