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91-468: Hansen Dam is a flood control dam in the northeastern San Fernando Valley , in the Lake View Terrace neighborhood of Los Angeles , California . The dam was built by the U.S. Army Corps of Engineers , Los Angeles District in 1940. Hansen Dam was named after horse ranchers Homer and Marie Hansen, who established a ranch in the 19th century. The Hansen Dam Recreation Center is located in

182-446: A canal's full capacity may cause flooding to spread to other waterways and areas of the community, which causes damage. Defenses (both long-term and short-term) can be constructed to minimize damage, which involves raising the edge of the water with levees , embankments or walls. The high population and value of infrastructure at risk often justifies the high cost of mitigation in larger urban areas. The most effective way of reducing

273-659: A 1 in 1000 year flood (light blue) and low-lying areas in need of flood defence (purple). The most sustainable way of reducing risk is to prevent further development in flood-prone areas and old waterways. It is important for at-risk communities to develop a comprehensive Floodplain Management plan. In the US, communities that participate in the National Flood Insurance Program must agree to regulate development in flood-prone areas. One way of reducing

364-494: A 1,300-acre (530 ha) reservoir , which is sometimes referred to as Hansen Lake. The spillway structure, outlet works and channel are located near the center of the Dam's rock embankment. The embankment itself follows a slight curve that creates a natural barrier by connecting the hills at either end of the dam. It is southeast of the city of San Fernando . The Los Angeles Flood of 1938 , which included significant flooding along

455-636: A broader set of strategies taken to reduce flood risk and potential impact while improving resilience against flood events. As climate change has led to increased flood risk an intensity, flood management is an important part of climate change adaptation and climate resilience . For example, to prevent or manage coastal flooding , coastal management practices have to handle natural processes like tides but also sea level rise due to climate change. The prevention and mitigation of flooding can be studied on three levels: on individual properties, small communities, and whole towns or cities. Flood management

546-525: A certain amount of space in which floodwaters can fill. Other beneficial uses of dam created reservoirs include hydroelectric power generation, water conservation , and recreation. Reservoir and dam construction and design is based upon standards, typically set out by the government. In the United States, dam and reservoir design is regulated by the US Army Corps of Engineers (USACE). Design of

637-556: A coast). The spawning grounds for fish and other wildlife habitats can become polluted or completely destroyed. Some prolonged high floods can delay traffic in areas which lack elevated roadways. Floods can interfere with drainage and economical use of lands, such as interfering with farming. Structural damage can occur in bridge abutments , bank lines, sewer lines, and other structures within floodways. Waterway navigation and hydroelectric power are often impaired. Financial losses due to floods are typically millions of dollars each year, with

728-621: A cooking feature in one of the northern drainages of the San Gabriel Mountains, are the oldest known from the central Transverse Ranges. Early material culture indicates extensive use of grinding implements to process small seeds, supplemented by hunting activities. Numerous cogged stones are also found within sites of this period, indicating ceremonial activities. During the Middle Period (5000 BP to 800 BP), sites generally indicate an increase in population and broadening of

819-517: A dam and reservoir follows guidelines set by the USACE and covers topics such as design flow rates in consideration to meteorological, topographic, streamflow, and soil data for the watershed above the structure. The term dry dam refers to a dam that serves purely for flood control without any conservation storage (e.g. Mount Morris Dam , Seven Oaks Dam ). Flood control channels are large and empty basins where surface water can flow through but

910-417: A flood does happen, the city can recover quickly and costs are minimized. For example, homes can be put on stilts, electrical and HVAC equipment can be put on the roof instead of in the basement, and subway entrances and tunnels can have built-in movable water barriers. New York City began a substantial effort to plan and build for flood resilience after Hurricane Sandy . Flood resilience technologies support

1001-652: A large area of the forest in and around the burned area until December 31, 2025. As of October 24, 2024, the fire had burned 55,126 acres (22,309 ha; 86 sq mi; 223 km ) and was 99 percent contained. The Angeles National Forest manages the habitats , flora and fauna ecosystems , and watersheds . Some of the rivers with watersheds within its boundaries provide valuable non- groundwater recharge water for Southern California . The existing protected and restored native vegetation absorb and slow surface runoff of rainwater to minimize severe floods and landslides in adjacent communities. The land within

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1092-565: A large role on the Forest, with commercial timber activities virtually ceasing in the Forest during the mid-1950s. The Great Hiking Era of the San Gabriel Mountains (AD 1880 – 1938) saw increasing use of the rugged backcountry for recreational purposes by the foothill communities, coinciding with the real estate boom in the lowlands and the great interest in hiking, hunting and fishing by the urban populations. In particular, six major hiking trails converged at Red Box Saddle. Settlements started inside

1183-641: A lowhead dam, is most often used to create millponds , but on the Humber River in Toronto, a weir was built near Raymore Drive to prevent a recurrence of the flood damage caused by Hurricane Hazel in October 1954. The Leeds flood alleviation scheme uses movable weirs which are lowered during periods of high water to reduce the chances of flooding upstream. Two such weirs, the first in the UK, were installed on

1274-442: A marked increase in regional population. Village provinces, composed of politically and economically-aligned villages may have existed during this period. Subsistence efforts in the mountains appear to focus on hunting, marked by the appearance of the bow and arrow. Greater regional interaction is marked by an increase in non-local materials, indicative of widespread interregional trade networks. The first reported European contact for

1365-405: A method of using water to control flooding was discovered. This was accomplished by containing 2 parallel tubes within a third outer tube. When filled, this structure formed a non-rolling wall of water that can control 80 percent of its height in external water depth, with dry ground behind it. Eight foot tall water filled barriers were used to surround Fort Calhoun Nuclear Generating Station during

1456-549: A month and was the worst in Los Angeles County history, charring 250 square miles (650 km ), approximately one-fourth of the forest; displacing wildlife, and destroying 91 homes, cabins and outbuildings and the family-owned Hidden Springs Cafe. During the fire, two firefighters died after driving off the Mt. Gleason County Road looking for an alternate route to get the inmates out at Camp 16. The Station Fire threatened

1547-469: A portion of the facility. AquaFence consists of interlocking panels which are waterproof and puncture-resistant, can be bolted down to resist winds, and use the weight of floodwater to hold them in place. Materials include marine-grade batlic laminate, stainless steel, aluminum and reinforced PVC canvas. The panels are reusable and can be stored flat between uses. The technology was designed as an alternative to building seawalls or placing sandbags in

1638-418: A result of California's growing housing crisis . In September 2015, a $ 300,000 cleanup effort was initiated. Flood control Flood management can include flood risk management, which focuses on measures to reduce risk, vulnerability and exposure to flood disasters and providing risk analysis through, for example, flood risk assessment . Flood mitigation is a related but separate concept describing

1729-694: A tiny section also extends westward into northeastern Ventura County , in the Lake Piru area. The San Gabriel Mountains National Monument , established in 2014 and managed by the U.S. Forest Service, is largely within the Angeles National Forest. The John D. Dingell Jr. Conservation, Management, and Recreation Act of 2019 established the Saint Francis Dam Disaster National Memorial and Saint Francis Dam Disaster National Monument at and around

1820-629: A total of 700,176 acres (1,094.0 sq mi; 2,833.5 km ), protecting large areas of the San Gabriel Mountains and Sierra Pelona Mountains . It is located just north of the densely inhabited metropolitan area of Greater Los Angeles . While primarily within Los Angeles County, a small part extends eastward into southwestern San Bernardino County , in the Mount San Antonio ("Mount Baldy") area, and

1911-629: A wide range of flood management methods including but are not limited to flood mapping and physical implication measures. Flood risk management looks at how to reduce flood risk and how to appropriately manage risks that are associated with flooding. Flood risk management includes mitigating and preparing for flooding disasters, analyzing risk, and providing a risk analysis system to mitigate the negative impacts caused by flooding. Flooding and flood risk are especially important with more extreme weather and sea level rise caused by climate change as more areas will be effected by flood risk. Flood mapping

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2002-559: Is a broad term that includes measures to control or mitigate flood waters, such as actions to prevent floods from occurring or to minimize their impacts when they do occur. Flood management methods can be structural or non-structural: There are several related terms that are closely connected or encompassed by flood management. Flood management can include flood risk management, which focuses on measures to reduce risk, vulnerability and exposure to flood disasters and providing risk analysis through, for example, flood risk assessment . In

2093-575: Is a flood defense system designed to protect people and property from inland waterway floods caused by heavy rainfall, gales, or rapid melting snow. The SCFB can be built to protect residential properties and whole communities, as well as industrial or other strategic areas. The barrier system is constantly ready to deploy in a flood situation, it can be installed in any length and uses the rising flood water to deploy. When permanent defenses fail, emergency measures such as sandbags , inflatable impermeable sacks, or other temporary barriers are used. In 1988,

2184-472: Is a tool used by governments and policy makers to delineate the borders of potential flooding events, allowing educated decisions to prevent extreme flooding events. Flood maps are useful to create documentation that allows policy makers to make informed decisions about flood hazards. Flood mapping also provides conceptual models to both the public and private sectors with information about flooding hazards. Flood mapping has been criticized in many areas around

2275-558: Is being restored , with invasive plants removal and native plant reintroduction. The proposed Rim of the Valley Trail Corridor would include Hansen Dam Park as a significant hub with trailheads. The Discovery Cube Los Angeles is located at the northwest corner of the recreation area on the intersection of Osborne St. and Foothill Blvd. It was built in November 2014 and was intended to serve as an extension campus of

2366-520: Is indicated and in such cases environmentally helpful solutions may provide solutions. Natural flooding has many beneficial environmental effects. This kind of flooding is usually a seasonal occurrence where floods help replenish soil fertility, restore wetlands and promote biodiversity . Flooding has many impacts. It damages property and endangers the lives of humans and other species. Rapid water runoff causes soil erosion and concomitant sediment deposition elsewhere (such as further downstream or down

2457-404: Is not retained (except during flooding ), or dry channels that run below the street levels of some larger cities , so that if a flash flood occurs the excess water can drain out along these channels into a river or other bodies of water . Flood channels are sometimes built on the former courses of natural waterways as a way to reduce flooding. Channelization of this sort was commonly done in

2548-735: Is part of environmental engineering . It involves the management of water movement, such as redirecting flood run-off through the use of floodwalls and flood gates to prevent floodwaters from reaching a particular area. Flood mitigation is a related but separate concept describing a broader set of strategies taken to reduce flood risk and potential impact while improving resilience against flood events. These methods include prevention, prediction (which enables flood warnings and evacuation), proofing (e.g.: zoning regulations), physical control ( nature-based solutions and physical structures like dams and flood walls ) and insurance (e.g.: flood insurance policies). Flood relief methods are used to reduce

2639-467: Is typified by the secularization of the Mission system, and the appearance of large land grants, called Ranchos. The major activities involved livestock and farming, and peripheral areas were regularly involved in these activities, as vaqueros sought out timber, water, prey, sport, and stray cattle and horses. Use of the highlands may have included seasonal livestock grazing, utilizing some of the springs in

2730-436: The 2011 Missouri River Flooding . Instead of trucking in sandbag material for a flood, stacking it, then trucking it out to a hazmat disposal site, flood control can be accomplished by using the on site water. However, these are not fool proof. A 8 feet (2.4 m) high 2,000 feet (610 m) long water filled rubber flood berm that surrounded portions of the plant was punctured by a skid-steer loader and it collapsed flooding

2821-681: The Discovery Cube Orange County . It has a mix of both traveling and permanent exhibits, which includes work done by the Los Angeles Bureau of Sanitation for waste reduction and resource conservation. It also has sponsored areas by the Los Angeles Department of Water and Power that educate visitors about sustainability, water conservation and preserving natural resources. In 2015, KTTV reported that unhoused people were camping at Hansen Dam as

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2912-487: The Mount Wilson Observatory atop Mt. Wilson . The site includes two telescopes, two solar towers, and transmitters for 22 television stations, several FM radio stations, and police and fire department emergency channels. Although the fire scorched one side of the outhouse at amateur-owned Stony Ridge Observatory, six miles northeast of Mt. Wilson, aside from minor damage from smoke and ash infiltration,

3003-485: The River Aire in October 2017 at Crown Point, Leeds city centre and Knostrop . The Knostrop weir was operated during the 2019 England floods . They are designed to reduce potential flood levels by up to one metre. Coastal flooding is addressed with coastal defenses, such as sea walls , beach nourishment , and barrier islands . Tide gates are used in conjunction with dykes and culverts. They can be placed at

3094-774: The United States Forest Service is located in the San Gabriel Mountains and Sierra Pelona Mountains , primarily within Los Angeles County in southern California . The ANF manages a majority of the San Gabriel Mountains National Monument . The national forest was established in 1908, incorporating the first San Bernardino National Forest and parts of the former Santa Barbara and San Gabriel National Forests . Angeles National Forest headquarters are located in Arcadia, California . The Angeles National Forest covers

3185-458: The 1960s, but is now often being undone, with "rechannelization" through meandering, vegetated, porous paths. This is because channellizing the flow in a concrete chute often made flooding worse. Water levels during a flood tend to rise, then fall, exponentially. The peak flood level occurs as a very steep, short spike; a quick spurt of water. Anything that slows the surface runoff (marshes, meanders, vegetation, porous materials, turbulent flow,

3276-477: The Angeles National Forest. It quickly burned through much of the eastern portion of the forest and the Sheep Mountain Wilderness . On September 10, it crossed into San Bernardino County after seeing rapid growth. Evacuation orders were prompted for Mount Baldy Village and Wrightwood as the fire approached the communities. The fire caused the Angeles National Forest to order closures for

3367-571: The City of Los Angeles Department of Recreation and Parks. Most facilities are accessed from Highways 5 and/or 210. The Hansen Dam Horse Park and Hansen Dam Aquatic Center are located behind the dam here, and Hansen Dam Golf Course in front. Recreation Center and Park features a moderate size lake which is filled with circulated drinking water and offers fishing and public boating. The lake is open year-round, including holidays, but may be closed during times of severe weather or for planned events. Also at

3458-502: The Forest boundaries in the forms of homesteads and resorts in the southern section, and, in the less steep northern section, ranches and homesteads. In 1891, the first homestead was filed in the Big Tujunga Canyon area, and others soon followed. Homestead patents were established throughout the range, with the last being granted on the Angeles National Forest in 1938. A number of resorts and camps sprang up, and these supported

3549-865: The San Gabriel Timberland Reserve was created by President Harrison. The creation of the Reserve, which was the forerunner of the Angeles, was in response to public concern about watershed values as early as 1883. Floods resulting from fire denuded slopes were causing problems with the lowland populations. In 1905, the Reserves were transferred from the Department of the Interior to the Department of Agriculture, and renamed National Forest in 1907. The San Gabriel National Forest consisted of

3640-789: The Tujunga Wash and at its confluence with the Los Angeles River , resulted in increased support to dam and channelize the city's creeks and rivers. In 1939, due to repeated floods and the damage they caused in the eastern portions of the San Fernando Valley, the U.S. Army Corps of Engineers began the project. The Corps worked in conjunction with the Los Angeles County Flood Control District (LACFCD). They had already considered planning to implement flood risk management within

3731-504: The amount of mitigation needed to protect humans and buildings from flooding events. Similarly, flood warning systems are important for reducing risks. Following the occurrence of flooding events, other measures such as rebuilding plans and insurance can be integrated into flood risk management plans. Flood risk management strategy diversification is needed to ensure that management strategies cover several different scenarios and ensure best practices. Flood risk management aims to reduce

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3822-520: The amount of storage capacity of the reservoir. As a result, in 1981, the Corps proposed raising the height of the dam rather than starting the expensive process of removing the build up of silt, sand, gravel and other debris. The proposal did not pass, and responsibility was redirected back to the Corps providing maintenance of the dam. The Corps must occasionally excavate sediment and vegetative debris to clear clogged outlet works and maintain full capacity of

3913-450: The area of the Angeles was in 1769 when the expedition of Gaspar de Portola traveled through the neighboring valleys on his way to Monterey. Early non-Native American use of the Forest centered on early explorers traveling through the area, while early land grants, missions, and townsites surrounded the Forest area. The construction of the missions of San Gabriel Archangel (1771) and San Fernando Rey de España (1797) cemented Spanish presence in

4004-432: The area since 1915 after a previous series of floods. In 1939 the Corps, by use of eminent domain , seized the horse ranch of Homer and Marie Hansen to build the dam. After a year of construction and over $ 11 million in initial costs, the dam and its corresponding facilities were finished. The 2-mile (3.2 km) long, 97-foot (30 m) high dam was built to control the runoff and floodwaters. During storms and flooding,

4095-559: The area. It was during this period that gold was discovered in Placerita Canyon, in 1842, the first authenticated discovery of gold in California. It started California's "first" gold rush. Soon after the later discovery of gold at Sutter’s Mill in 1848, and subsequent conflict between the United States and Mexico, California became part of the United States. Almost immediately large numbers of American migrants began crossing

4186-650: The building site, including scour protection for shoreline developments, improving rainwater in filtration through the use of permeable paving materials and grading away from structures, and inclusion of berms , wetlands or swales in the landscape. When more homes, shops and infrastructure are threatened by the effects of flooding, then the benefits of protection are worth the additional cost. Temporary flood defenses can be constructed in certain locations which are prone to floods and provide protection from rising flood waters. Rivers running through large urban developments are often controlled and channeled. Water rising above

4277-601: The capacity of stormwater systems. This separates stormwater from blackwater , so that overflows in peak periods do not contaminate rivers. One example is the SMART Tunnel in Kuala Lumpur. Some methods of flood control have been practiced since ancient times. These methods include planting vegetation to retain extra water, terracing hillsides to slow flow downhill, and the construction of floodways (man-made channels to divert floodwater). Other techniques include

4368-417: The construction of levees, lakes, dams, reservoirs, retention ponds to hold extra water during times of flooding. Many dams and their associated reservoirs are designed completely or partially to aid in flood protection and control. Many large dams have flood-control reservations in which the level of a reservoir must be kept below a certain elevation before the onset of the rainy/summer melt season to allow

4459-823: The construction of the Plaza Church in El Pueblo de Nuestra Señora la Reina de los Angeles de Porciuncula (now just ‘Los Angeles’). It has also been said that timbers for the San Fernando Mission came from the Tujunga Canyons, and for the San Gabriel Mission came from Little Icehouse Canyon and Little Santa Anita Canyon. With the Independence of Mexico in 1821, the area of the Forest came under Mexican control. The Mexican Period

4550-473: The context of natural hazards and disasters , risk management involves "plans, actions, strategies or policies to reduce the likelihood and/or magnitude of adverse potential consequences, based on assessed or perceived risks". Flood control , flood protection , flood defence and flood alleviation are all terms that mean "the detention and/or diversion of water during flood events for the purpose of reducing discharge or downstream inundation". Flood control

4641-552: The dam is intended to catch water within the reservoir. Provisions in the dam's standards of operations promote water conservation efforts coordinated with the Los Angeles County Department of Public Works . The provisions allow the dam to discharge water onto spreading grounds located south of the dam, which then percolates into groundwater recharge basins and is stored as part of the city's water supply. Accumulation of debris from previous floods reduced

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4732-535: The dam. In the mid-1940s, the Hansen Dam Basin's recreational possibilities were considered as it attracted thousands of visitors every year. Development of recreational facilities began in 1952 with the creation of Holiday Lake, which was used by swimmers, boaters, and anglers. By 1991, the lake had become completely filled with sediment and was abandoned. The Hansen Dam Recreation Center and Park are located here, with extensive day use facilities operated by

4823-568: The damage caused by flooding is to remove buildings from flood-prone areas, leaving them as parks or returning them to wilderness. Floodplain buyout programs have been operated in places like New Jersey (both before and after Hurricane Sandy ), Charlotte , North Carolina, and Missouri . In the United States, FEMA produces flood insurance rate maps that identify areas of future risk, enabling local governments to apply zoning regulations to prevent or minimize property damage. Buildings and other urban infrastructure can be designed so that even if

4914-504: The desert. Merchants and landowners settled in communities throughout the southern California region. Miners poured into the mountains primarily following original and modified Indian trails. Large placer and lode mining operations were established in the San Gabriels, with mixed success. Although the mountains were honeycombed with quartz veins, and a host of small mines were gouged out of the slopes in an attempt to strike gold, many of

5005-541: The effects of flood waters or high water levels during a flooding event. They include evacuation plans and rescue operations. Flood relief is part of the response and recovery phase in a flood management plan. Floods are caused by many factors or a combination of any of these generally prolonged heavy rainfall (locally concentrated or throughout a catchment area), highly accelerated snowmelt , severe winds over water, unusual high tides, tsunamis , or failure of dams, levees , retention ponds , or other structures that retained

5096-443: The fast recovery of individuals and communities affected, but their use remains limited. Flooding can occur in cities or towns as urban flooding . It can also take place by the sea as coastal flooding . Sea level rise can make coastal flooding worse. In some areas there are also risks of glacial lake outburst floods . There are many adaptation options for flooding: More frequent drenching rains may make it necessary to increase

5187-761: The fire's effect on dormant seeds, that lasted for several years. The plant produces prolific lavender flowers. Unfortunately, as visitors to the Forest discovered, contact with it may cause a poison-oak-like rash. Tree species for which the forest is important include bigcone Douglas-fir ( Pseudotsuga macrocarpa ), Coulter pine ( Pinus coulteri ), and California walnut ( Juglans californica ). The National Forest also contains some 29,000 acres (12,000 ha) of old growth , with Jeffrey pine ( Pinus jeffreyi ) forests, as well as mixed conifer forests (with Coast Douglas-fir ( Pseudotsuga menziesii var. menziesii ), ponderosa pine ( Pinus ponderosa ), white fir ( Abies concolor ), and lodgepole pine ( Pinus contorta ) being

5278-547: The flood control basin and surrounding slopes behind the dam. Hansen Dam and its once-designed lake are now seasonal flood spreading grounds in the San Fernando Valley on Tujunga Wash . Tujunga Wash begins between the San Gabriel Mountains and Verdugo Mountains . The dam is 1 mile (1.6 km) downstream from the confluence of the Big Tujunga Creek and Little Tujunga Creek-Wash. The dam contains

5369-758: The flow", and deliberately flood some low-lying areas, ideally vegetated, to act as sponges, letting them drain again as the floodwaters go down. Excess water can be used for groundwater replenishment by diversion onto land that can absorb the water. This technique can reduce the impact of later droughts by using the ground as a natural reservoir. It is being used in California, where orchards and vineyards can be flooded without damaging crops, or in other places wilderness areas have been re-engineered to act as floodplains. In many countries, rivers are prone to floods and are often carefully managed. Defenses such as levees, bunds , reservoirs, and weirs are used to prevent rivers from bursting their banks. A weir, also known as

5460-435: The forest is diverse, both in appearance and terrain. Elevations range from 1,200 to 10,064 ft (366 to 3,068 m). The Pacific Crest Trail crosses the forest. Much of this National Forest is covered with dense chaparral shrub forests with oak woodlands , which changes to pine and fir-covered slopes in the higher elevations. Subsequent to the fire there was a heavy growth of poodle-dog bush , apparently triggered by

5551-441: The gate. A flood barrier , surge barrier or storm surge barrier is a specific type of floodgate , designed to prevent a storm surge or spring tide from flooding the protected area behind the barrier. A surge barrier is almost always part of a larger flood protection system consisting of floodwalls , levees (also known as dikes), and other constructions and natural geographical features. The self-closing flood barrier (SCFB)

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5642-520: The human and socio-economic losses caused by flooding and is part of the larger field of risk management . Flood risk management analyzes the relationships between physical systems and socio-economic environments through flood risk assessment and tries to create understanding and action about the risks posed by flooding. The relationships cover a wide range of topics, from drivers and natural processes, to models and socio-economic consequences. This relationship examines management methods which includes

5733-535: The incident. The fire was brought under control at 1:00   p.m. on 2 November, having burned 2,028 acres (8.21 km ). In the Station Fire, more than 161,000 acres (650 km ) of the forest were burned by an arson fire that began on August 26, 2009, near Angeles Crest Highway in La Cañada and quickly spread, fueled by dry brush that had not burned for over 150 years. The fire burned for more than

5824-411: The increasing numbers of hikers and campers who forged into the wilderness.  In 1889, the first telescope made its arduous journey up to the summit of Mt. Wilson. A small observatory of canvas and wood, run by Harvard and USC astronomers, was later replaced in 1904 by the more famous institution run by George Ellery Hale. Mount Wilson Observatory would quickly rise to dominate astronomy worldwide. It

5915-488: The integration of flood risks and required policies. In flood management, stakeholder engagement is seen as an important way to achieve greater cohesion and consensus. Integrating stakeholder engagement into flood management often provides a more complex analysis of the situation; this generally adds more demand in determining collective solutions and increases the time it takes to determine solutions. Angeles National Forest The Angeles National Forest ( ANF ) of

6006-587: The lowlands but relied heavily on the mountains for water, building supplies, and game. By 1800, local Native American traditional cultural lifestyles of had largely disappeared due to devastating European influences, including diseases and incorporation into the Mission System. The first documented instance of timber activity in the local mountains was in 1819 when Joseph Chapman cut down timber in Millard Canyon (also called Church Canyon) for use in

6097-422: The main drivers of floods interact with each other. Flood modelling combines factors such as terrain, hydrology , and urban topography to reproduce the evolution of a flood in order to identify the different levels of flooding risks associated with each element exposed. The modelling can be carried out using hydraulic models, conceptual models, or geomorphic methods. Nowadays, there is a growing attention also in

6188-625: The most abundant trees). This forest is home to black bears , gray foxes , bobcats , mountain lions , mule deer , bighorn sheep , rattlesnakes and coyotes . A National Forest Adventure Pass is required for parking at many locations in the Angeles National Forest and other National Forests in Southern California , and this can be obtained online or from visitor centers and local merchants. Los Angeles County has declared that passes are not required on county-maintained roads. There are also many other areas that do not require

6279-427: The mouth of streams or small rivers, where an estuary begins or where tributary streams, or drainage ditches connect to sloughs . Tide gates close during incoming tides to prevent tidal waters from moving upland, and open during outgoing tides to allow waters to drain out via the culvert and into the estuary side of the dike. The opening and closing of the gates is driven by a difference in water level on either side of

6370-489: The nearby Angeles National Forest , and a walking pathway along the dam's top. The habitats include montane chaparral and woodlands and riparian in the rustic areas. The basin is a resource of large open space for the Los Angeles region. A large portion of the area remains undeveloped in an effort to conserve natural habitats and maintain the diverse animal and plant species. The Hansen Dam Park natural area's ecology

6461-439: The path of floodwaters. Other solutions, such as HydroSack , are polypropylene exteriors with wood pulp within, though they are one-time use. There are several methods of non-structural flood management that form part of flood risk management strategies. These can involve policies that reduces the amount of urban structures built around floodplains or flood prone areas through land zoning regulations. This helps to reduce

6552-539: The production of maps obtained with remote sensing . Flood modelling is helpful for determining building development practices and hazard mitigation methods that reduce the risks associated with flooding. Stakeholder engagement is a useful tool for flood risk management that allows enhanced public engagement for agreements to be reached on policy discussions. Different management considerations can be taken into account including emergency management and disaster risk reduction goals, interactions of land-use planning with

6643-402: The region. In the first two decades of the 19th Century, the Mission System drew in large numbers of Indian neophytes for baptism, completely changing the cultural landscape of the area. A number of subordinate Missions, or Estancias, were built with native labor as outposts to serve as mission-affiliated ranchos, overseeing localized operations. The Spanish Missions generally occupied the lands in

6734-551: The remainder of the observatory and its historic 30-inch Carroll telescope survived. In September and October 2020, the Bobcat Fire burned 115,796 acres (180.931 sq mi) (468 km ) in the central San Gabriel Mountains of the Angeles National Forest. It was one of the largest wildfires in Los Angeles County history. On September 8, 2024, the Bridge Fire broke out near East Fork and Glendora Mountain roads in

6825-402: The resource base in response to population pressure and resource stress. This period is represented by a large array of specialized subsistence sites, characterized as villages, base camps, food processing and procurement sites, special use sites, rockshelters, pictographs, ovens, and cemeteries. A Late Period (800 BP to AD 1769) proliferation of sites within the Angeles National Forest indicates

6916-572: The risk to people and property is through the production of flood risk maps. Most countries have produced maps which show areas prone to flooding based on flood data. In the UK , the Environment Agency has produced maps which show areas at risk. The map to the right shows a flood map for the City of York , including the floodplain for a 1 in 100-year flood (dark blue), the predicted floodplain for

7007-455: The river spreading over a floodplain) will slow some of the flow more than other parts, spreading the flow over time and blunting the spike. Even slightly blunting the spike significantly decreases the peak flood level. Generally, the higher the peak flood level, the more flood damage is done. Straight, clear, smooth concrete-walled channels speed up flow, and are therefore likely to make flooding downstream worse. Modern flood control seeks to "slow

7098-490: The ruins of the St. Francis Dam in the Forest's San Francisquito Canyon . The Angeles National Forest contains five nationally designated wilderness areas . Two of these also extend into neighboring San Bernardino National Forest : Early Native American cultural sites in the inland mountain regions corresponding with the Angeles National Forest are sparse, Radiocarbon dates of 7675 and 7600 years Before Present (BP), taken from

7189-502: The site is located a smaller swim lake which features water that is filtered and chlorinated and has a capacity of 2,800 swimmers. The City of Los Angeles Department of Recreation and Parks provides lifeguards who service to the three lakes within the flood control basin. The recreation center and park areas also have: picnic tables and barbecue pits, children's play areas; and baseball diamonds and soccer fields. The park features equestrian and walking trails, that link to those exploring

7280-724: The southern section of the present day Angeles and portions of the San Bernardino Forest. In 1908, the name was changed to Angeles National Forest. In 1926, the eastern area was divided and San Bernardino National Forest recreated. At this time, the Saugus (now part of the Santa Clara-Mojave Rivers Ranger District) was detached from the Santa Barbara Reserve and joined with the Angeles. The San Gabriel Forest Reserve

7371-432: The spike. Even slightly blunting the spike significantly decreases the peak flood level. Generally, the higher the peak flood level, the more flood damage is done. Modern flood control seeks to "slow the flow", and deliberately flood some low-lying areas, ideally vegetated, to act as sponges, letting them drain again as the floodwaters go down. Where floods interact with housing, industry and farming that flood management

7462-622: The venture. In its height at the turn of the century, the Mount Lowe Railway was the most popular tourist attraction in California, comparable to a modern-day Disneyland. In its 43 year history, it saw over three million recorded visitors. In 1938, the most destructive rainstorm in recent memory washed away so much of the track that the railway was abandoned. Much of the ruins of the Mt Lowe Railway are still accessible above Pasadena for interpretive hikes. On December 20, 1892,

7553-439: The ventures were inactive by 1896. The last flurries of serious mining in the region largely ended by the late 1930s. Building of major roads began in the 1850s and railroads passed through Soledad Canyon and Cajon Pass a short time later. Don Benito Wilson, in 1864, built a road into the Forest to harvest wood for fence posts, wine barrels, pickets and shingles. With the majority of Forest composed of chaparral, timber has not played

7644-400: The water. Water levels during a flood tend to rise, then fall, very abruptly. The peak flood level occurs as a very steep, short spike; a quick spurt of water. Anything that slows the surface runoff (marshes, meanders, vegetation, porous materials, turbulent flow, the river spreading over a floodplain) will slow some of the flow more than other parts, spreading the flow over time and blunting

7735-461: The water. Flooding can be exacerbated by increased amounts of impervious surface or by other natural hazards such as wildfires, which reduce the supply of vegetation that can absorb rainfall. During times of rain, some of the water is retained in ponds or soil, some is absorbed by grass and vegetation, some evaporates, and the rest travels over the land as surface runoff . Floods occur when ponds, lakes, riverbeds, soil, and vegetation cannot absorb all

7826-500: The world, due to the absence of public accessibility, technical writing and data, and lack of easy-to-understand information. However, revived attention towards flood mapping has renewed the interest in enhancing current flood mapping for use as a flood risk management method. Flood modelling is a tool used to model flood hazard and the effects on humans and the physical environment. Flood modelling takes into consideration how flood hazards, external and internal processes and factors, and

7917-419: The worst floods in recent U.S. history having cost billions of dollars. Property owners may fit their homes to stop water entering by blocking doors and air vents, waterproofing important areas and sandbagging the edges of the building. Private precautionary measures are increasingly important in flood risk management. Flood mitigation at the property level may also involve preventative measures focused on

8008-766: Was a movement to create the Sierra Madre National Park, but that never occurred. On September 30, 1925, portions of the Angeles National Forest and the Cleveland National Forest were detached to re-establish the San Bernardino National Forest . Angeles National Forest is registered as California Historical Landmark #717, for being the first National Forest in the state. The campgrounds at Broken Blade, Twisted Arrow and Pima Loops were closed on July 26, 2013, after squirrel infected with bubonic plague

8099-478: Was discovered. On 1 November 1966, a fire started at 5:19   a.m. on the Los Pinetos Nike Site (LA-94). The fire spread, threatening medical facilities and residential areas south edge of the national forest. 12 firefighters with United States Forest Service 's El Cariso "Hot Shot" crew were killed when they were caught in a flare up in a canyon. 11 more firefighters were seriously burned in

8190-672: Was established on December 20, 1892, the San Bernardino Forest Reserve was established on February 25, 1893, and the Santa Barbara Forest Reserve was established on December 22, 1903. Together, they became National Forests on March 4, 1907, and they were combined on July 1, 1908, with all of the San Bernardino forest and portions of San Gabriel forest and Santa Barbara forest composing the new Angeles National Forest. In 1916, there

8281-528: Was home to the world's two largest telescopes as well as the most powerful facilities in existence for studying the sun. In 1891, preliminary work began on an electric cable incline railway from Rubio Canyon to Echo Mountain, a feat never before attempted in the world. Professor Thaddeus S. C. Lowe, an energetic entrepreneur who had garnered fame in the Civil War by ballooning for the Union Army, undertook

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