“The Keynote of All Flood Control Measures is Conservation”: Reports of the Board of Engineers on Flood Control to the Los Angeles County Board of Supervisors, July 1915, Part Three

by Paul R. Spitzzeri

This third part of our intensive review of the important July 1915 report by engineers to the Los Angeles County Board of Supervisors about how to conduct a comprehensive and carefully crafted flood control program takes us to the section by Henry Hawgood, chair of the Board of Engineers responsible for the document. Hawgood was an expert on water issues for the powerful Southern Pacific railroad company and was an advocate for countywide flood control measures for about a quarter-century, not long after the major flood of 1889.

His more matter-of-fact approach meant a very brief introductory passage describing the boundaries of the San Gabriel District as “coterminous with the San Gabriel Valley, plus the Whittier Narrows, (Paso de Bartolo,) as far south as the Whittier Road [Boulevard].” From the San Gabriel Mountains (which he, as many did, called the Sierra Madre) to that thoroughfare and from the Arroyo Seco to the line with San Bernardino County embraced an area of 325 square miles, with a little more than 140 west of the San Gabriel River and nearly 180 east of the principal watercourse.

Moreover, Hawgood continued, in addition to flood waters coming from the valley section, some 227 square miles, there were waterways to carry flow from 322 square miles “of precipitous mountain country.” About three-quarters of that area drained through the expansive San Gabriel Canyon, beelow which a dozen square miles emptied into the river from the west and almost fifty from the east. The Río Hondo, the old channel of the San Gabriel, incorporated drainage of some 37 square miles, as well.

For that latter, the sources included such canyons as Rubio, Eaton, Little and Big Santa Anita, and Sawpit, while a couple from the west, such as Fish Creek, were tributary to the San Gabriel. In the valley floor there were drainages of some 97 square miles, about 75% from “west of Duarte and the Lexington Wash, the upper portion of the Río Hondo.

To the east of the San Gabriel River, was the system including the Little and Big Dalton washes coming out of the mountains at Glendora, the San Dimas element, Walnut Creek and San José Creek—this latter running from Pomona to the San Gabriel River including as the southern boundary to the Homestead, then owned by Thurston Pratt and Eugene Bassett.

Most of the area within San Gabriel Canyon were above evenly divided between the West Fork (just under 105 square miles) and the East Fork (just over 103), with fewer than 17 square miles from the canyon mouth to the junction of those branches. Hawgood noted that rainfall “is of secondary importance in matters of Flood Control” though adding that main factors was the highest hourly level of precipitation for small areas and the maximum daily and monthly total for bigger ones, along with “the occurrence and continuity of preceding rains.” He added that “rain gauges (the only pair were at the observatories at Mt. Wilson and Mt. Lowe) should be established at several selected locations in the mountains and flood stream measuring stations” where principal watercourses headed into the valleys.

A map showing rainfall levels for the severe flood period of 18-21 February 1914 included a table of inches recorded during those four days, ranging from two inches at San Pedro up to over 19 at Mt. Lowe and Mt. Wilson, while Pasadena recorded over 11, Azusa above 13, and Sierra Madre almost 16 inches.

In a section titled “Maximum Floods,” Hawgood wrote that knowing the highest levels of floodwaters carried in streams was basic to studying floods and conservation and that “it is selfevident that all questions as to capacity of channels, sufficiency of levees and their protection, erosion and silting, and the conservation of water, rest primarily on the maximum volume of water to be controlled at any one time.” For the San Gabriel River, however, “they have never been measured” at that maximum level. While good information existed about the major floods of 1884 and 1889, there were some earlier major floods but “which are too remote to furnish information of engineering value.”

Hawgood provided some testimony by long-time residents of the region in a court case involving a local railroad company and damages sought against it after the 1889 inundation. Surveyor Edward T. Wright, said that, despite the fact that he took no nots, “my memory is that the flood of 1884 was about as much as that of 1889,” which was corroborated by Antonio María Lugo, Jr., who staated “the flood of 1884 was just like the other one.” Juan C. Sepulveda, from another prominent Californio family like the Lugos, stated that the biggest floods were in 1825, 1833 and 1862, before official records began in 1877.

William Mulholland, the architect of the Los Angeles Aqueduct and many dams in the region, stated that “the greatest flood I ever observed was December 24th, 1889” with one taking place on 17 February 1884 being the second greatest inundation. He estimated that twice the water was in the Los Angeles River in that latter than the former. Former mayor Stephen C. Foster, who married into the Lugo family, opined that “in the fifty years I have known the river, I have only known five or six of these floods; the greatest that I can remember is that of 1889.”

Jacob C. Cox stated that he’d lived in Los Angeles since 1858 and could recall four or five floods, with his recollection that “the highest, I think, was in 1862 or 1863 [it was late 1861/early 1862].” Cox, a plasterer who was accused of participating in the rioting that led to the lynching of 18 men and a teen in the horrific Chinese Massacre of 24 October 1871 but who was not tried, felt that the 1889 flood “was very high” but added that “I did not see as much of it as I did that of 1862 and 1863.”

George Dalton, apparently the nephew of Rancho Azusa’s Henry Dalton, the namesake of the Dalton washes, said he was “acquainted with the Los Angeles River for over 45 years” and of the five or six major floods, that of 1862 was the worst. J.S. Hutchins, who came to the area just after that major inundation was living in Pacoima Canyon in 1889 and that was the worst in his experience. Meanwhile, Hawgood calculated that the ratio of 1889 to 1914 was 1.77 to 1.

Much of the report concerns maximum discharges of flood waters in the watercourses within the district, with the 1889 flood being viewed as the best barometer of maximum flow, accounting for the fact that such early floods as in 1825, 1833 or 1862 might have been worse and future inundations of those magnitudes likely. There is some highly technical material in this section before Hawgood addressed conservation noting that it “can be and sould be an important economic factor in flood control work.”

Included here were the building of retarding dams in smaller mountain canyons and spreading grounds at the debris cones at the mouths of the larger canyons emptying into the valleys. Building these would also reduce the size and cost of flood control channels “which will still be a necessity to convey the remaining surplus waters harmlessly to the sea.” Getting a better handle on precipitation levels in the mountains, through the rain gauges noted above, would better help determine the extent and costs of these elements.

Hawgood stated that conservation work would not take place quickly and then addressed the types of dams, despite Olmsted’s reporting on this topic, needed in the mountains, including vertical and inclined examples. He observed that “the primary effect . . . is to reduce the natural velocity of the stream” and, in so doing, “to reduce the erosive and transporting power of the stream and as a corollary induce sedimentation.”

When it came to check dams, it was important to limit the sand and gravel deposits and he cited the example of a dam in Triunfo Canyon at the extreme west end of the San Fernando Valley near modern Westlake Village, which was built just two years before but already was more than half filled with debris, even if there was still some decent water storage. Check dams also had major benefits for limiting erosion of the beds and banks of watercourses. There was also the question of absorption through spreading, with an instance given of work along San Antonio Creek at the eastern limits of the county near Claremont.

Reforestation was also highlighted, but specifically directed towards the natural brush cover on mountain slopes, not the planting of trees. The presence of low-growing chaparral would greatly assist in the prevention of erosion from heavy rains, though more trails would need to be built because of the density. Still, this was considered less costly than trying to care for new forest trees planted instead and, on steep slopes, this was the only practicable strategy to employ.

As to levees, Hawgood cited stdies of the Mississippi, Rhine and Po rivers to state “the writer is of the opinion that if only one method for flood control could be adopted, it would necessarily be levees.” This is because “flood retardation and conservancy within practical limits on the upper waters [in the mountains] cannot in themselves be sufficiently potent to relieve the lower lands from destructive floods.” What they would do, though is “be of the greatest aid in accomplishing flood control” and in providing significant economic value. Consequently, retardation “should be prosecuted to its full practical limit” which would limit levees and channel improvements in the valleys.

At the Arroyo Seco, an 80-foot high dam at Devil’s Gate above Pasadena was highly recommended for both flood mitigation and water storage. For the Alhambra Wash, which ran behind the property where the Temple family lived in the city of that name from late 1917 to 1923, extending a cement portion past that location and to the Southern Pacific line to the south was recommended with bank protection and rectification called for to the Río Hondo terminus. Other courses in the western part of the district were suggested for other moderate improvements, such as drops in the beds, improvements on banks, permanent side walls, and others.

For the San Gabriel River, check dams in smaller water courses and at higher elevations, spreading rounds at the mouth, diversion of waters to the Río Hondo, levees, weirs, redesign of the bridge for Pomona (Valley) Boulevard, establishing desirable widths of the riverbed, and others. Not recommended were large dams, though those were to come in later years. The Río Hondo was talked about as if it was always a separate course from the San Gabriel, so that Hawgood wrote that “prior to 1884 it appears to have had only a small flood water contribution from the San Gabriel,” though perhaps it was understood that the course change was seventeen years prior to that. He added that, after floods in 1889 and 1891, he was active in promoting control work from the canyon to El Monte, though to no avail.

He added that the channel turned sharply west just below what is now Valley Boulevard and a pocket of significant length and depth was such that it would grow and cause future flood problems. Hawgood continued that “below the Old Mission Bridge a similar condition exists,” this being just east of where the Temples were living in 1915 before oil was found on their property. The idea was to keep the watercourse at 330 feet width to Whittier Boulevard and a weir built at its head to keep flow from the San Gabriel to a desired and manageable level.

At Peck Road and just below that the channels of Sawpit and the Santa Anita canyons discharged into the river, with Eaton Wash coming in not far south, followed by Rubio Wash. A full capacity of water would be embraced with these discharges, though it was added that Alhambra Wash came in after them. Levees or dikes were to be built along the 11 1/2 mile course, with those at the major bends noted earlier, were “of particular importance.”

With Little and Big Dalton washes, it was proposed to join the two as well as to straighten the course, which had stone or wood walls on private lands, but “much of the channel is in poor condition.” A storm drain near the Glendora ranch of Judge Charles Silent was recommended for extension, while levees using boulders was also suggested, along with building concrete walls, bank protection. Check dams in the mountains feeding these courses “would go far to reduce the peak floods, while spreading could be done at the base of the mountains.” The two were to convey waters with Walnut Creek, which needed general channel and bank protection.

The San Dimas wash provided, Hawgood reported, plenty of boulders for building levees, while near the Santa Fe Railway line pits for railroad ballast were also good for that purpose. With 45-degree turns in two spots, a good deal of erosion was in evidence, while private property owners built fences and wing dams but not with success. What was needed was the “rectification of [the] channel, and protection works done on a concerted plan,” so that the creek would not cut through south and cause more damage.

Moreover, “a channel change of about 2,500 feet in length is necessary at Azusa Avenue in northwest Covina” and a sharp S-bend continued west to Lark Ellen Avenue, just beyond which the wash meets the Little and Big Dalton courses, though reference here was made to San Dimas meeting Walnut Creek, which then empties into the San Gabriel River just below where Interstates 10 and 605 meet now. What was called “Mount Reservoir” and where a maximum 124-foot high dam was possible but where “flood control may be obtained by mountain check dams at less cost” to impound water appears to be where the San Dimas Dam and Reservoir were built in the Twenties.

Finally, Live Oak and Thompson creeks above Claremont “form the head waters of the San Jose, which discharges into the San Gabriel in the Whittier narrows.” Check dams were called for in the mountains to limit flooding, which “would benefit not only the Claremont-Lordsburg [La Verne] country, but all the Puente Valley, where, again, the creek formed the southern limits of the 75-acre Workman Homestead. Hawgood noted, however, that “further surveys are necessary to outline the nature and extent of control works in the Claremont-Lordsburg country.”

As for San Jose, specifically, he merely observed: “little needed except channel clearing.” San Antonio Creek, forming the boundary between Los Angeles and San Bernardino counties, was such that, if private parties spreading the waters at the base of the mountains continued plans for improvement, “there will be need of little if any protective works on this creek within Los Angeles County.

In the final section, there were cost estimates for work based on using steam shovels in smaller channels and drag line scrapers in larger ones. As mentioned already, levees on the latter would use boulders and, if these were not available, 4-inch concrete slabs with ribs on the undersides to forestall slippage on the upper portion and articulated mats for flexibility on the lower section, with an apron extending six feet into the bed.

If the levee was of fine sand, a coarse blanket was to be used, or a sprinkling of hot asphalt oil (this was tried successfully at the Silver Lake Reservoir, northwest of downtown Los Angeles), though the first was preferred “as it forms a base with which the concrete of the slabs will cohere.” For the former, “a mat made by laying wire netting” on the slope and then out into the bed and covered with cobbles and small boulders with more netting on top and wiring the two nets together into a kind of quilt was suggested. This was recently tried at La Tuna Canyon where Sun Valley is today at the east end of the San Fernando Valley.

Brush protection, especially through the planting of willows and bamboo were encouraged in locales where the earth had enough moisture to support these materials and Hawgood observed that “bamboo is particularly promising, [as] it is readily propagated and is of dense growth.” Later, however, it was found that arundo donax, used extensively to prevent erosion of canals of all kinds was so invasive and flammable that it has caused serious issues in many areas of the region. Dykes, though, were not recommended by Hawgood because their protective qualities were generally insufficient.

Finally, there were estimates of cost for structures and rights-of-way, the latter obviously needed through acquisition from private landowners. For the San Gabriel River and RíoHondo, the costs were just shy of $2.5 million. West of that, from Pasadena to Monrovia/Duarte, the total was near $1.3 million. East of San Gabriel Canyon to the county line at San Antonio Creek, the figure was slightly less than that of the western portion. In all, structures were pegged at close to $4.4 million and rights-of-way about $583,000.

We’re pick up the reporting with Charles Leeds’ examination of the Coastal Plain district, south of Ballona, downtown Los Angeles, and Whittier Narrows and including the vital area of the harbors at San Pedro/Wilmington/Long Beach. Please check in with us for that fourth part of this post!

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