 Dam failures are catastrophic events. The sheer magnitude of the destruction they reap is unimaginable. One such disaster in 1963 caught live on TV would show the world the potential havoc that can be inflicted on a community. A failure to recognise the risks of poor site selection would show that the Los Angeles Department of Water and Power had not learned the lessons from the St Francis Dam nearly 30 years earlier. The event did however show the benefits of regular inspections, as even though failure would destroy hundreds of homes and run into the cost of millions, the death toll was a relatively modest five. It was seen that the Baldwin Hills Dam failure was assured when the project was green lit, but heroic actions on the day limited the potential for tragedy. As such I'm going to rate it here four on my disaster scale, but here on the legacy scale as it was one of the first dam failures caught on live TV. Welcome to a brief history of the Baldwin Hills Dam and Reservoir Failure. Our story starts just before the Second World War and the plan to build a reservoir to supply the South LA neighbourhood of Baldwin Hills with safe and reliable drinking water. LA throughout its life has been plagued by droughts, which was the usual reason for the LA aqueduct system and the ill-fated St Francis Dam. As the city expanded into different suburbs, naturally the need for basic amenities such as electricity, roads and of course water arose. The project started to undertake surveys of a proposed site in 1939, but wouldn't get underway until the mid-1940s. The site selected was atop one of the tallest hills in the region in the Baldwin Hills area. This was to make use of an already existing ravine, but this convenient location came at a big cost. This was that the location for the new reservoir was above the Inglewood fault line and the site area itself was formed at the subsurface of loose sandy soil. The engineers were aware of the associated challenges of building on such an area and set out to design the project to be resistant to erosion and seismic activity. The reservoir was going to be relatively small compared to some other projects undertaken by the Los Angeles Department of Water and Power, only impounding around 900 acre feet of water at an average depth of 65 feet. The comparison, the St Francis Dam, was intended to hold back 38,000 acre feet and whilst we're on the subject, both projects had something else in common, well apart from catastrophic failure and that was designers. Long on were the days of Moe Holland, but the lead in the Baldwin Hills project was Ralph Proctor towards the end of his career, but at the beginning he had worked under the former civil engineer during the St Francis Dam designing construction. Proctor had become over the following decades post St Francis failure and authority on new methods of control soil compacting, in doing so becoming the person responsible for design and construction and maintenance of all dams in the Los Angeles water system. The design of the reservoir made use of a steep ravine by excavation at the abutments and filling in the eroded valleys. The reservoir was to be held back on free size by compacted earth dikes with the Baldwin Hills dam on the northern face creating a roughly square shape and all of the structure was going to be earthen. The main consideration for the engineers was preventing water seepage which is one of the main risks to an earthen dam, as this can cause erosion and ultimately total failure, like what would happen to Teton in the 1970s. To prevent this the Los Angeles Department of Water and Power devised a lining around the reservoir basin to stop seepage into the dam's foundations. The lining consisted of a 10 foot thick line of compacted clay tapering down to five feet at the top of the embankments. This was placed on a quarter inch asphalt membrane which itself was sprayed onto the subgrade soils in two coats. Between the clay lining and the asphalt membrane a cemented pea gravel drain was constructed to collect any seepage, sending it to a central observation and measuring station called the drainage inspection chamber. On top of all of this another asphalt coating was applied. A separate foundation drainage system was also provided and additional tile drains at the toes of the reservoir slopes and a special fault drain was installed and fed directly into the drainage inspection chamber. All these drains allowed effective monitoring of the structure for any seepage. The design relied heavily on the clay lining to prevent seepage and if any would occur the technicians on the project could observe the amount easily. If any cracks occurred in the clay it was thought that the asphalt membrane would still hold out any significant erosion. With the ability to properly monitor seepage it was thought that ample time would be available to drain the reservoir and undertake repairs. Construction began in 1947 and in 1949 an inactive fault was discovered necessitating the modification of the positioning of the gate tower. Worries were raised during the design and construction of the project on the suitability of the structure and its location. The concern emerged from the active fault line and unsuitable foundational material. Lead engineer Ralph Proctor, not the type of man to accept criticism, proceeded with the project according to his own design. Construction was completed in 1951. By this time the Baldwin Hills dam reached a height of 232 feet and stretched a total of 650 feet in length. As a result of the design considerations of the reservoir after filling in 1951 the dam and embankments were frequently inspected and monitored. All would seem well for around 12 or so years until one such routine inspection revealed something worrying. Around 11.15 am the reservoir's caretaker noticed that brown water had begun draining from the pipes underneath the asphalt membrane liner. This hinted that water was seeping towards the foundations. At 11.30 am he figured out that the northeast and southeast tow drains and the fault drain were discharging muddy water in the inspection chamber, which as we've seen in disasters before, that dirty water means erosion. Shortly after the alarm was raised and by 12.20 pm the outlet works were engaged to empty the reservoir but this would take at least 24 hours. Because of this the Los Angeles Department of Water and Power contacted the police to evacuate downstream from the reservoir. Around 1600 residents would be successfully evacuated all whilst workers above them frantically attempted to show up the failing dam and clear out the emergency discharge pipes. At 2.20 pm lowering of the reservoir water level revealed a free foot wide break in the reservoirs in a lining. An attempt was made to try and plug the hole with sandbags but this proved ineffective. The efforts would be in vain as at 15.38 am the Baldwin Hills Dam failed, releasing some 250 million US gallons of stored water down onto the residential buildings below. Interestingly the breach was captured by KTLA using a helicopter. The footage dramatically illustrated the pure power of the tidal wave of destruction. The well timed and shot failure is something we take for granted today with 24 hour coverage but for 1963 this was rather unique. Within an hour and a half it was all over. The reservoir was now virtually empty, five lives were lost and millions of dollars of damage was inflicted. Although tragic the disaster was a testament to the quick response of the caretaker, operating engineer, LADWP and evacuation personnel. With so much destruction the next question that had to be asked was how did the dam that had worked and been monitored for 12 years fail so quickly and dramatically. Needless to say the failure sprouted several investigations and has been a key learning point for the dam engineering industry. The extensive drainage system wasn't as perfect as originally it seemed. Because of calcium carbonate deposits developing necessitating frequent cleaning and maintenance this caused a reduced amount of seepage to enter the inspection chamber leading to ineffective measurement of potentially eroding water. Throughout its operating history the reservoir was emptied a couple of times due to cracks in the clay and asphalt and leading up to 1963 the flows from discharging horizontal drains under the main dam varied rapidly. After the reservoir was fully drained the damage to the asphalt paving clay cap and membrane could be fully seen. There were significant cracks which allowed water to erode away at the foundations of the dam. The damage to the lining has been theorized to have been caused by a number of factors either on their own or combined. During construction heavy machinery was allowed to travel over the fragile asphalt causing hairline cracks in the surface and emptying and filling a reservoir could have caused stress fractures and effects due to nearby oil filled repressurization. Another factor could have been from tectonic movement from the nearby Inglewood fault line that had weakened the structure and lining. It was found that during oil drilling works to the south of the dam that drilling fluids were lost in the upper several hundred feet hinting at cavities and fractures in the foundation rock. It could be taken that this was similar underneath the reservoir as well. It is thought that the lining and membrane had been ruptured throughout its life allowing seepage into the unknown cavities underneath the dam as well as the known inactive fault lines. The resulting erosion reached a tipping point which could have been the cause of the total structural failure. The cause of the failure was and still remains a case open for study. In the early 1970s discovery of faulting and surface seepage of oil filled waste brines along the fault near the south of reservoir showed that oil filled injection of waste disposal and improved recovery of oil could have been a significant cause of the failure. This triggered hydraulic fracturing aggravating movements on the fault traversing the reservoir on the day of the failure. The reservoir was never refilled and is now part of the community park because of the disaster it's thought to be around 12 million dollars but luckily it wasn't higher due to the actions of everybody on that December day. 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