“Restraining the Impetuous Run-Off of Flood Flows”: Reports of the Board of Engineers on Flood Control to the Los Angeles County Board of Supervisors, July 1915, Part Two

by Paul R. Spitzzeri

We continue our deep dive into a seminal 1915 document for early flood control planning in Los Angeles County with Frank H. Olmsted’s portion of the Reports of the Board of Engineers on Flood Control to the Los Angeles County Board of Supervisors. The civil engineer provided a summary of the Mountain District, which he was assigned a year earlier and for which there was some 744 square miles. His cost estimate of just above $5.3 million was for impeding dams and furrowing contours of watercourses in the mountains, building masonry dams at the Arroyo Seco and Tujunga, constructive rock fill dams at Eaton Canyon, Pacoima and San Gabriel Canyon, providing spreading grounds for over 6300 acres at San Antonio, San Dimas, San Gabriel, Pacoima and Tujunga canyons, rectifying and controlling the Haines and Blue Gum, Sycamore and Verdugo channels, and forestry work.

Olmsted began his report by observing the damages incurred from floods were small compated to what would come “unless a wise policy of control is energetically pursued from this time on. Removal of brush from settlement and development, erosion, and poor channel conditions were cited as major problems. He noted that, in central Europe, countries invested huge sums for flood control and those methods could be applied in Los Angeles County to not only limit flooding “but also provide large additional water supplies during the dry periods of the year, when such supplies are needed.”


Olmsted’s suggestions “for restraining the impetuous run-off of flood flows” went from the county line at Claremont and Upland on the east to the Pacific on the west and, while data was incomplete for his estimates, the type of work to be done, the funds required, and the results achieved “have been sufficiently investigated to furnish an intelligent basis for the plans.” A mix of two masonry dams, rock fill dams in other locales, the spreading grounds for five streams, and “rebrushing and reforestation of mountain slopes,” were all core elements.

Notably, Olmsted posited that much of the failure of ancient societies was from the allowance for “careless overdrafts on nature’s resources” and avoiding this in Los Angeles County was necessary by protecting the fertile plains and limiting the runoff of soils to the Pacific. He aded that water impounding was initially expensive but “generally succeeds in accomplishing the purpose,” while diverting water through channels to the ocean “is apt to be only an expedient” and, while less costly, also lacked security and would be a disappointment over time.


Local conditions, though, required flood channels, but limiting silt and debris through conservation in the mountains were important to the success of those channels; therefore providing for both major methods was key. He added that the often-stunning velocity of flood flows was such that these “destroy almost any works that can building on anything but bedrock” but could even erode that “and destroy masonry when the water carried grit and sand.” Simply put, restricting water from pouring down steep slopes limited damage below.

Olmsted added that “it is a well known fact that the opportunity for storing flood flow in large reservoirs in Los Angeles County does not exist,” something that would change later, but he stated that, at Devil’s Gate where the Arroyo Seco came out of the San Gabriels, and in Tujunga Canyon, were two places where these conditions did exist. He averred that “if relief from the intolerable flood conditions in Los Angeles County had to come from surface reservoir storage alone, that portion of the County subject to overflow would be doomed.” Similarly, limiting work only to improving channels in the valleys and plains would not mitigate the damage from materials washed down from the mountains.


The engineer continued to suggest that “the spreading of the flood flows on the gravel cones below the canyon mouths while a very important conservation measure, does not promise any great relief from the maximum flood flows on account of the limits of its application.” Borrowing from Julius Caesar, Olmsted advocated for the strategy of “divide and conquer,” by “attacking these great floods at their sources in the high mountains before they have become united and irresistible.” Employing storage, spreading and channel work, “we will be able to permanently relieve the people of Los Angeles County from the menace of future floods.”

Olmsted then reviewed a very heavy flood period from February 1914 and looked at efforts carried out in Europe to mitigate flood damage. He wrote of experiments conducted at Haines Canyon, just east of Tujunga and where run off during the storm was the highest yet recorded in the region. At Clear Creek, which empties into Big Tujunga Creek well within the canyon of that name, more field testing was done concerning flows and mitigation efforts in smaller canyons tributary to larger ones.


With respect to rebrushing and reforestation, the engineer stated that destruction of native plant materials due to fire, flood, mudslides and other activity meant that what was needed was “a systematic effort to offset these conditions by an intelligent program” including planting brush on slopes and planting such trees as alders, laurels and willows in the canyon beds, where check dams would also allow for water even during the driest of times during mid-summer.

Further details on the western sections of the district were provided as to conditions and recommendations at Wilson Creek, above Sylmar, Pacoima Creek, Little Tujunga, Big Tujunga, the Tujunga (Hoyt) Reservoir, Crescenta and Verdugo and areas along the south face of what he called the “Hollywood Mountains” and which we know as the Santa Monicas. With this latter, it wasn’t as if there was anywhere near the volume of water involved that would be found in the San Gabriel range, but there was “much anxiety during flood seasons . . . [in] a long strip of very highly improved land, which, as a residential section, is considered by many to the choicest in the world.” Obviously, these areas would only become “choicer” in succeeding years.


More central in the district were the Arroyo Seco; Millard, Rubio and Las Flores canyons; Big and Little Santa Anita canyons; Eaton Canyon; Sawpit Canyon (above Monrovia); Fish Canyon along the west side of the mouth of San Gabriel Canyon; and the huge expanse of that latter. Further east included Little and Big Dalton canyons (above Glendora); San Dimas Canyon; Thompson Creek (above Claremont); and the large San Antonio Canyon watershed.

Throughout these sections, there is very technical detail with regard to water flow and the characteristics of dams, weirs, channels are other components to be utilized in the proposed work. The next section, then, was a report on the San Fernando District by Joseph B. Lippincott, widely known at the time for his work on the Los Angeles Aqueduct, but usually less remembered subsequently than Fred Eaton and William Mulholland.


Lippincott’s summary of conclusions was concise and indicated that the value of land in the San Fernando Valley “meanced by floods of the Los Angeles River and its tributaries” was $30 million, while lesser concern existed for the section of the river between the newly established film studio community of Universal City and the confluence with the Arroyo Seco. The estimated total of work to provide flood protection for the areas of the river north and west of the Arroyo, but not including the Verdugo area nor any work in the mountains, was $2.15 million.

It was added that there were over 3,100 acres called for public ownership to allow “for the purpose of spreading storm water and the filling of underground reservoirs.” Such work was “urgently recommeded,” but it was still important to build levees and protect the banks of the river and tributaries. As noted by Olmsted, “the crest of the flood waters will not be substantially diminished by the process of spreading, because of the volume and muddiness of water.


Noting Olmsted’s report on recommended mountain improvements, Lippincott observed that such work would reduce water volume and the limitation of debris which would be left in the valleys. Even if retarding dams were not built, he continued, “it will be necessary to control the great floods by means of a system of levees.” Field testing was needed to determine “the best methods of proceeding with this mountain flood retardation” and how effective these would be.

As to flood channels, these were to be built in the northern and western sections of the valley, not just to carry storm water “but also to furnish adequater waterways for purposes of draining these lands when they become saturated through the process of irrigation.” This, of course, shows how agricultural the vast majority of the valley was. Finally, Lippincott stated that ownership of channels “should be promptly obtained by some adequate public authority so that protective measures could enacted when needed.


In describing the geographical situation, he wrote that there was one outlet, this being the downslope through which the river traveled in the southeastern corner near Glendale and the eastern one-third portion had steeper slopes and absorbent gravel sections for better storage potential, whereas the western two-thirds was flatter and had denser soil for less capture of ground water.

As to the Los Angeles River it “originates from the more porous soils of the eastern section” of the valley and, once underground water hit the Cahuenga [Santa Monica] range, “it is brought to the surface” and “of marked constancy and purity” save when major floods hit, though smaller flows and some of the water in major events were absorbed in that underground supply. This consistency of volume allowed for the founding of Los Angeles in 1781 and sufficient supply for many years afterward. Lippincott added that, while much of the water in the western section was lost due to evaporation among heavier soils, development with streets, sidewalks and storm drains, would send more water to that southeastern corner.


The most damaging floods were those that came with large volumes of water issuing from Little and Big Tujunga canyons, though massive accumulations of debris meant that water “spreads in various channels just as the fingers of a hand will radiate from the wrist when the open hand is pressed upon a table.” This along with a great amount of water and significant velocity of flow “produce the great menace in the San Fernando Valley.” Five channels over a 7-mile width carried water through that section and high quantities of debris also contributed to the spread as well as the shifting of the watercourses.

Pacoima Creek, carrying awater through the Van Nuys area, did not foment the destruction of the Tujungas, but it did “cause inconvenience and damage” to orchards, roads and other elements. What took place in the west, due again to the soil composition, was sheets of water at a shallow depth which, with silting, covered roads and farmlands, though not to the extent found in the extreme east of the valley. James W. Reagan conducted field work that showed that there were 45,000 acres in the latter subject to flood damage with the value of land some $20 million, but such studies had not yet been done in the western two-thirds, though the value there was determined to be half of the eastern third.


Lippincott reiterated that the steepness of the mountains at Tujunga and Pacoima canyons precluded the building of large capacity reservoirs. While a 105-foot high dam in Pacoima would have been filled in about 4 1/2 hours by the maximum volume from the biggest storn of 1914, its value would still be significant because of the impounding of water for use in the area and having something there to limit flood damage was, of course, better than nothing at all. Similarly, a 140-foot dam on the Big Tujunga would have been full after 4.3 hours. It was noted that a reservoir built in the mid-1890s near Chatsworth was far smaller in capacity than floor runoff and so, it was filled with silt and no longer could impound water.

As for spreading grounds, the nearly 30,000 acres of gravel in the eastern edge was such that, Lippincott averred, no well ever got to bedrock there and so storage capacity was quite significant (at least for that time!) and enough to hold all of the maximum yearly flow of local streams. The problem, of course, was to divert and control flood waters flowing in large volumes, though efforts with the Santa Ana River in the eastern San Bernardino Valley were cited in this connection, though there were problems with mud and other debris clogging the spreading grounds.


Consequently, the engineer warned “it is not wise to raise false and exaggerated hopes as to what can be done in conserving these excessive flood discharges.” Conservation was necessary, and the plans would allow for as much of that as feasible, but so was the fact that “substantial levees must be built across the valleys to project the excessive flood discharges into the sea.” What followed was discussion of the Pacoima diversion and suggestions for improving its banks with levees, establishing a more controlled channel, providing for spreading grounds and other work; and recommendations for what to do with the Little and Big Tujunga creeks with respect to directing waters more consistently in the western and northern channels, along with levee construction and over 2600 acres of spreading grounds.

There were also discussions of sand and gravel and rock fills, as well as planting of banks to forestall erosion, with the date palm as being considered the best tree because it was hardy and energetic, possessed a strong and wide-spread root system and branches that formed an effective barrier. The western section of the valley, including the Chatsworth, Wilson’s, San Fernando, and Zelzah creeks and channels, as well as the Los Angeles River were covered. The latter “is poorly defined” in the western end and channels would need to be built to better direct flow.


As the river moved eastward along the base of the Caheunga (Santa Monica) Mountains, there were issues with heavy stands of willow and cottonwood trees in the bottom lands, so that “the flood channels become clogged, the rush of waters accumulates barriers against the trees causing a diversion of the flood and oushing of it into the cultivated areas of the north.” It was mentioned that in the prior winter, some two miles of the river were cleared east of the newly created film studio community of Universal City, so that “a moderate flood occupied its old course through this cleared line and excavated its bed from one to four feet.” This “was resisted by the roots and stumps of the trees which were exposed to the erosion.”

From Rancho Encino east to Verdugo Wash, which came out of Glendale and met the river where today’s Interstate 5 and 134 Freeway meet, work was limited to “clearing, grubbing and the keeping clear of a channel some 300 feet in width,” while “the natural growth of bush and trees is to be left on both sides of the channel for the protection of the banks,” though date palms could be added to fill in gaps. From Verdugo Wash to the Arroyo Seco, Lippincott noted, the river was up to 20 feet deep and 2,000 feet wide, but “in this area of bottom lands the river is apt to wander with considerable freedom and violence during periods of great floods.”


Near Griffith Park, the City of Los Angeles owned bottom lands had had its diversion works for domestic water supply in this area. In some cases, “the natural and dense growth of timber in these park areas and the cultivation of the privately owned fields down to the park line on the north” meant that the river left its channel and went onto private land, so it was proposed to clear the old channels and keep the river within city-owned areas. Again, with natural willow and cottonwood trees, as well as introduction of the date palm, it was hoped that a somewhat economical plan could be implemented to provide for a more managed flow of the river. It was also hoped that a Pacific Electric Railway trestle bridge near Tropico and Ivanhoe near Atwater Village and Glassell Park could be replaced so that piles impeding flow would be removed in favor of a girder or truss type of span.

Further south, the use of planting, rip rap levees and other work were proposed to protect banks. At and near the confluence with the Arroyo Seco, where the Southern Pacific freight yards were situated, it was recommended that the channel be kept to at least 300 feet in width and cleared of all trees in the bed. Near what was the Los Angeles Pigeon Farm until those February 1914 inundations destroyed the facility, there was an area of “approximately 525 acres of lands that are highly cultivated for garden purposes,” but the river was so frequently flooded “that it is covered with sand unsuitable for cultivation and is generally abandoned as a flood channel.” It was hoped that much private land from the west Tujunga channel to the Arroyo Seco would be granted as rights of way to the county and city so that “this district will keep the channel clear and will construct the bank protection work” called for in the report.


After reiterating the cost estimates for the work in the district, Lippincott discussed a study of excavators that could be used for the improvements contemplated, including a series of cost estimates and a schematic showing machines with varying boom sizes, angles of application, bucket sizes and other elements. Finally, there is a series of sixteen plates showing the washes and creeks of Tujunga, Pacoima and San Fernando and several views of the Los Angeles River at Griffith Park, near Tropico, and at the junction with the Arroyo Seco.

Tomorrow, we’ll pick up the story with the reports by Henry Hawgood of the San Gabriel District and Charles Leeds for the Coastal Plain District, so please join us then.

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