Misplaced Pages

#574425

56-518: Lake Hodges has a total capacity of 30,251 acre-feet of water. Water level elevation in the lake is maintained at a maximum of 280 feet (85 m) above sea level, 35 feet (11 m) lower than the dam's maximum of 315 feet (96 m) spillway to ensure safe operations. The lake level can fluctuate significantly, depending upon the amount of runoff received from the San Dieguito River drainage basin. Interstate 15 crosses Lake Hodges via

112-402: A fuse plug . If present, the fuse plug is designed to wash out in case of a large flood, greater than the discharge capacity of the spillway gates. Although many months may be needed for construction crews to restore the fuse plug and channel after such an operation, the total damage and cost to repair is less than if the main water-retaining structures had been overtopped. The fuse plug concept

168-443: A baffle of concrete blocks but usually have a "flip lip" and/or dissipator basin, which creates a hydraulic jump , protecting the toe of the dam from erosion. Stepped channels and spillways have been used for over 3,000 years. Despite being superseded by more modern engineering techniques such as hydraulic jumps in the mid twentieth century, since around 1985 interest in stepped spillways and chutes has been renewed, partly due to

224-506: A battlefront that covers many miles. While the battles of other ant species generally constitute colony raids lasting a few hours, or skirmishes that occur periodically for a few weeks, Argentine ants clash ceaselessly; the borders of their territory are a site of constant violence and battles can be fought on top of hundreds of dead ants. Fights may be halted by adverse weather such as rain. In contrast, native populations are genetically more diverse and form colonies that are much smaller than

280-431: A deeper nesting ant species abandons their nest, Argentine ant colonies will readily take over the space. Because the native habitat for this species is within riparian floodplains, colonies are very sensitive to water infiltration within their nests; if their nests become inundated with water, workers will collect the brood and the entire colony will move to dry ground. Austrian entomologist Gustav L. Mayr identified

336-463: A few dams lack overflow spillways and rely entirely on bottom outlets. The two main types of spillways are controlled and uncontrolled. A controlled spillway has mechanical structures or gates to regulate the rate of flow. This design allows nearly the full height of the dam to be used for water storage year-round, and flood waters can be released as required by opening one or more gates. An uncontrolled spillway, in contrast, does not have gates; when

392-565: A plunge pool, or two ski jumps can direct their water discharges to collide with one another. Third, a stilling basin at the terminus of a spillway serves to further dissipate energy and prevent erosion. They are usually filled with a relatively shallow depth of water and sometimes lined with concrete. A number of velocity-reducing components can be incorporated into their design to include chute blocks, baffle blocks, wing walls, surface boils, or end sills. Spillway gates may operate suddenly without warning, under remote control. Trespassers within

448-628: A population of nearly one trillion individuals. Conflict does occur between members of different supercolonies. In 1997, UC San Diego researchers observed fighting between different Argentine ants kept in lab, and in 2004 scientists began to map out the boundaries of the different supercolonies that clashed in San Diego. On the border of the Very Large Colony and the Lake Hodges Colony thirty million ants die each year, on

504-604: A retreating motion in the winter. This has to do with soil moisture and temperature conditions. At the edges of these borders are either rival L. humile colonies or other obstacles that prevent further expansion, such as an inhospitable environment for nests. The ants are ranked among the world's 100 worst invasive animal species . In its introduced range, the Argentine ant often displaces most or all native ants and can threaten native invertebrates and even small vertebrates that are not accustomed to defending against

560-523: A spillway gate can result in the stranding of fish, and this is usually avoided. Argentine ant The Argentine ant ( Linepithema humile , formerly Iridomyrmex humilis ) is an ant native to northern Argentina , Uruguay , Paraguay , Bolivia and southern Brazil . This invasive species was inadvertently introduced by humans on a global scale and has become established in many Mediterranean climate areas, including South Africa , New Zealand , Japan , Easter Island , Australia,

616-419: A spillway to regulate downstream flow—by releasing water in a controlled manner before the reservoir is full, operators can prevent an unacceptably large release later. Other uses of the term "spillway" include bypasses of dams and outlets of channels used during high water, and outlet channels carved through natural dams such as moraines . Water normally flows over a spillway only during flood periods, when

SECTION 10

#1732801387575

672-499: Is a structure used to provide the controlled release of water downstream from a dam or levee , typically into the riverbed of the dammed river itself. In the United Kingdom, they may be known as overflow channels . Spillways ensure that water does not damage parts of the structure not designed to convey water. Spillways can include floodgates and fuse plugs to regulate water flow and reservoir level. Such features enable

728-460: Is designed like an inverted bell , where water can enter around the entire perimeter. These uncontrolled spillways are also called morning glory (after the flower ), or glory hole spillways. In areas where the surface of the reservoir may freeze, this type of spillway is normally fitted with ice-breaking arrangements to prevent the spillway from becoming ice-bound. Some bell-mouth spillways are gate-controlled. The highest morning glory spillway in

784-443: Is set by dam safety guidelines, based on the size of the structure and the potential loss of human life or property downstream. The United States Army Corps of Engineers bases their requirements on the probable maximum flood (PMF) and the probable maximum precipitation (PMP). The PMP is the largest precipitation thought to be physically possible in the upstream watershed. Dams of lower hazard may be allowed to have an IDF less than

840-469: Is significantly out of their reach. The city has a volunteer program, managed by Kayaking For The Birds , which maintains all of the lake's shoreline areas, keeping it free of discarded fishing line and other angling supplies, as well as all other litter which could pose a threat to birds and wildlife. It is home to the Lake Hodges Colony of Argentine ants. Spillway A spillway

896-604: Is used where building a spillway with the required capacity would be costly. A chute spillway is a common and basic design that transfers excess water from behind the dam down a smooth decline into the river below. These are usually designed following an ogee curve . Most often, they are lined on the bottom and sides with concrete to protect the dam and topography. They may have a controlling device and some are thinner and multiply-lined if space and funding are tight. In addition, they are not always intended to dissipate energy like stepped spillways. Chute spillways can be ingrained with

952-461: The Azores , Europe , Hawaii , and the continental United States . Argentine ants are significant pests within agricultural and urban settings, and are documented to cause substantial harm to communities of native arthropods , vertebrates, and plants within their invaded range. Linepithema humile is a small-bodied (2.2–2.6 mm) ant species, dull light to dark brown in color. Within

1008-662: The Lake Hodges Bridge . Approximately 1,000 feet (300 m) west of the I-15 freeway bridge is a bicycle/pedestrian bridge which opened on May 15, 2009, and is the longest stressed ribbon bridge in the world. Lake Hodges Dam is a multiple-arch dam that sits on the San Dieguito River. It was commissioned by the Volcan Water Company and designed by John S. Eastwood . It was completed in 1918 (106 years ago)  ( 1918 ) , and later purchased by

1064-410: The Argentine ant has in some cases displaced native ants that disperse the seeds of Fynbos plants like Mimetes cucullatus . The Argentine ants don't take the seeds underground and are left on the surface, resulting in ungerminated plants and the dwindling of Fynbos seed reserves after veld fires . Argentine ants sometimes tend aphid , mealybug , and scale insect colonies, sometimes relocating

1120-463: The PMF. As water passes over a spillway and down the chute, potential energy converts into increasing kinetic energy . Failure to dissipate the water's energy can lead to scouring and erosion at the dam's toe (base). This can cause spillway damage and undermine the dam's stability. To put this energy in perspective, the spillways at Tarbela Dam could, at full capacity, produce 40,000 MW; about 10 times

1176-430: The ability to store 20,000 acre-feet (25,000,000 m) of water at Hodges Reservoir for emergency use. This system is also used to provide electrical power to the grid during high demand times of the day. Water is pumped from Lake Hodges to Olivenhain at night when demand (and rates) for electricity is low. It is then flowed back down through generators during peak demand times. In 2019 a hypolimnetic aeration system

SECTION 20

#1732801387575

1232-418: The aggressive ants. This can, in turn, imperil other species in the ecosystem , such as native plants that depend on native ants for seed dispersal, or lizards that depend on native ants or invertebrates for food. For example, the recent severe decline in coastal horned lizards in southern California is closely tied to Argentine ants displacing native ant species on which the lizards feed. In South Africa,

1288-449: The amount of food available to the larvae. Argentine ant colonies almost invariably have many reproductive queens, as many as eight for every 1,000 workers. The seasonal low occurs in mid-winter, when 90% of a representative colony consists of workers and the remainder of queens, and no reproductive activity and minimal birthing. Eggs are produced in late-winter, nearly all of which hatch into sexual forms by May(*). Mating occurs after

1344-496: The bait is 25% water, with 0.5–1.0% boric acid or borate salts . In spring, during a colony's growth phase, protein based baits may be more effective due to much higher demand from the egg-laying queens. Due to their nesting behavior and presence of numerous queens in each colony, it is generally impractical to spray Argentine ants with pesticides or to use boiling water as with mound building ants. Spraying with pesticides has occasionally stimulated increased egg-laying by

1400-407: The capacity of its power plant. The energy can be dissipated by addressing one or more parts of a spillway's design. First, on the spillway surface itself by a series of steps along the spillway (see stepped spillway ). Second, at the base of a spillway, a flip bucket can create a hydraulic jump and deflect water upwards. A ski jump can direct water horizontally and eventually down into

1456-508: The city expects to complete construction of a new dam to replace this one. The reservoir has to be kept at a low elevation of 280 feet due to safety concerns, which means that the city can't access the water. Lake Hodges is a popular location for hiking, birding, fishing, kayaking, windsurfing, photography, and picnicking. It is surrounded by the hiking trails of the San Dieguito River Park and those trails are connected to

1512-873: The city of San Diego. Water from the Lake Hodges Reservoir services the customers of the Santa Fe Irrigation District and the San Dieguito Water District. The dam is 131 ft tall and 729 ft wide. In 2005, the San Diego County Water Authority , in conjunction with the City of San Diego , began work on a pipeline to connect Hodges Reservoir with Olivenhain Reservoir . The project was completed in 2012. The connection provides

1568-509: The diet were eventually incorporated into the cuticle of the subjects. Those that had the same diet appeared to recognize one another as kin. Those who had at least some overlap in dietary composition also appeared to react non-aggressively to one another. These interactions contrasts drastically with the groups that fed on completely different sources, such as those who lived off flies and those that fed on grasshoppers . The groups appeared to have incorporated hydrocarbons that were not similar to

1624-414: The difference in height between the intake and the outlet to create the pressure difference required to remove excess water. Siphons require priming to remove air in the bend for them to function, and most siphon spillways are designed to use water to automatically prime the siphon. One such design is the volute siphon, which employs volutes or fins on a funnel to form water into a vortex that draws air out of

1680-474: The females emerge. Worker production increases steadily from mid-March(*) to October(*), after which their numbers are not replenished; thus, their numbers drop steadily over the winter months. ((*) Note that the information regarding the months May, March, and October in this paragraph, as well as the entire Month axis in the graph, are most likely not worldwide correct, in special in Southern hemisphere, due to

1736-778: The first specimens of Hypoclinea humilis in the vicinity of Buenos Aires , Argentina in 1866. This species was shortly transferred to the genus Iridomyrmex , and finally to Linepithema in the early 1990s. The native range of Argentine ants is limited to riparian habitats in the lowland areas of the Paraná River drainage, which stretches across northern Argentina, Uruguay, Paraguay, and southern Brazil. Within South America, this species has spread into parts of Chile , Colombia , Ecuador , and Peru . Linepithema humile thrives in Mediterranean climates, and over

Lake Hodges - Misplaced Pages Continue

1792-423: The flood is sometimes expressed as a return period . A 100-year recurrence interval is the flood magnitude expected to be exceeded on the average of once in 100 years. This parameter may be expressed as an exceedance frequency with a 1% chance of being exceeded in any given year. The volume of water expected during the design flood is obtained by hydrologic calculations of the upstream watershed. The return period

1848-425: The introduced Argentine ants seldom attack or compete with each other, unlike most other species of ant. In their introduced range, their genetic makeup is so uniform that individuals from one nest can mingle in a neighboring nest without being attacked. Thus, in most of their introduced range, they form supercolonies . The Very Large Colony, which covers territory from San Diego to beyond San Francisco , may have

1904-687: The introduced range, first reported in California in 2000, then in Europe in 2002, Japan in 2009, and Australia in 2010. Several subsequent studies used genetic , behavioral, and chemical analyses to show that introduced supercolonies on separate continents actually represent a single global supercolony. The researchers stated that the "enormous extent of this population is paralleled only by human society", and had probably been spread and maintained by human travel. They have been extraordinarily successful, in part, because different nests of

1960-473: The invasion zone, ant colonies are large and include many workers and multiple queens. Argentine ants are opportunistic with regard to nesting preferences. Colony nests have been found in the ground, in cracks in concrete walls, in spaces between boards and timbers, even among belongings in human dwellings. In natural areas, they generally nest shallowly in loose leaf litter or beneath small stones, due to their poor ability to dig deeper nests. However, if

2016-438: The lake is home to nesting pairs of the least Bell's vireo , an endangered species. Two other threatened bird species, the California gnatcatcher and the coastal cactus wren , can be found in the areas around the lake. When water levels are up, and remain consistent, it is possible to observe the courtship and parenting behaviors of the western grebe as well as Clark's grebe . Both species can be seen seasonally nesting at

2072-408: The larvae of the pollinators . Argentine ants are a common household pest, often entering structures in search of food or water (particularly during dry or hot weather), or to escape flooded nests during periods of heavy rainfall. When they invade a kitchen, it is not uncommon to see two or three queens foraging along with the workers. Borate -sucrose water baits are toxic to Argentine ants, when

2128-455: The maximum level of the lake 20 feet below the spillway. Due to its advanced age, Lake Hodges had been closed to the public so the dam could undergo repair work. The water level was lowered in May 2022, when routine maintenance revealed cracks and defects, which turned the dam repairs into a yearlong process. On June 2, 2023, the dam, lake, and recreation area opened to the public again. Around 2034,

2184-404: The others and created an unfamiliar identity cue. These groups reacted violently towards each other. This suggests that dietary factors affect the recognition cues for colony members. Like workers in many other ant species, Argentine ant workers are unable to lay reproductive eggs but can direct the development of eggs into reproductive females; the production of males appears to be controlled by

2240-409: The parasites to unaffected plants, and their protection of these plant pests from predators and parasitoids can cause problems in agricultural areas. In return for this protection, the ants benefit by feeding off an excretion known as "honeydew" . There is also evidence that the presence of Argentine ant may decrease the number of pollinators that visit natural flowering plants via predation on

2296-404: The park's 65 miles of trails . The Audubon Society has proclaimed Lake Hodges and vicinity to be a Globally Important Bird Area . The ability to see almost 200 bird species attracts many birders as well as amateur and professional photographers. Fishing is allowed 9 months of the year and near record sized Largemouth Bass have been caught in the lake. The riparian habitat surrounding

Lake Hodges - Misplaced Pages Continue

2352-515: The past century it has spread to across the globe by human-mediated transport. The species has become established to every continent except Antarctica and includes many oceanic islands . The absence of aggression within Argentine ant colonies was first reported in 1913 by Newell & Barber, who noted "…there is no apparent antagonism between separate colonies of its own kind". Later studies showed that these " supercolonies " extend across hundreds or thousands of kilometers in different parts of

2408-468: The queens, compounding the problem. Pest control usually requires exploiting their omnivorous dietary habits, through use of slow-acting poison bait (e.g. fipronil , hydramethylnon , sulfluramid ), which will be carried back to the nest by the workers, eventually killing all the individuals, including the queens. Researchers from the University of California, Irvine , have developed a way to use

2464-428: The reservoir has reached its capacity and water continues entering faster than it can be released. In contrast, an intake tower is a structure used to control water release on a routine basis for purposes such as water supply and hydroelectricity generation. A spillway is located at the top of the reservoir pool. Dams may also have bottom outlets with valves or gates which may be operated to release flood flow, and

2520-411: The reservoir is controlled by the mechanical gates. In this case, the dam is not designed to function with water flowing over the top if it, either due to the materials used for its construction or conditions directly downstream. If inflow to the reservoir exceeds the gate's capacity, an artificial channel called an auxiliary or emergency spillway will convey water. Often, that is intentionally blocked by

2576-459: The river downstream. One parameter of spillway design is the largest flood it is designed to handle. The structures must safely withstand the appropriate spillway design flood (SDF), sometimes called the inflow design flood (IDF). The magnitude of the SDF may be set by dam safety guidelines, based on the size of the structure and the potential loss of human life or property downstream. The magnitude of

2632-422: The scent of Argentine ants against them. The exoskeletons of the ants are covered with a hydrocarbon-laced secretion. They made a compound that is different, but similar, to the one that coats the ants. If the chemical is applied to an ant, the other members of the colony will kill it. Another approach for a large scale control of the Argentine ant has been proposed by researchers from Japan, who showed that it

2688-404: The shallow eastern end of the lake. However, the lake's pumping system can raise or lower the water level by quite a few inches every day; these fluctuations can potentially cause the raft-like, floating grebe nests to float to shore, run aground, and be at risk of predation by carnivorous animals. In the event that a nest is beached, it will be subsequently abandoned by the parents, especially if it

2744-421: The shift of six months in seasons between the two hemispheres.) Colonies in the Argentine ant's native habitat are kept within a range of ten to one hundred meters by colonies of interspecific and intraspecific rivals. As the colonies expand, they appear to form fluctuating territory borders, which contract and expand on a seasonal and conditional basis. There is an expansive push outward in the summer months, with

2800-414: The spillway are at high risk of drowning. Spillways are usually fenced and equipped with locked gates to prevent casual trespassing within the structure. Warning signs, sirens, and other measures may be in place to warn users of the downstream area of sudden release of water. Operating protocols may require "cracking" a gate to release a small amount of water to warn persons downstream. The sudden closure of

2856-441: The supercolonies that dominate the introduced range. Colonies living in close proximity are territorial and aggressive toward one another. Argentine ants in their native South America also co-exist with many other species of ants, and do not attain the high population densities that characterize introduced populations. In a series of experiments, ants of the same colony were isolated and fed different diets. The hydrocarbons from

SECTION 50

#1732801387575

2912-424: The system. The priming happens automatically when the water level rises above the inlets. The ogee crest over-tops a dam, a side channel wraps around the topography of a dam, and a labyrinth uses a zig-zag design to increase the sill length for a thinner design and increased discharge. A drop inlet resembles an intake for a hydroelectric power plant, and transfers water from behind the dam directly through tunnels to

2968-474: The use of new construction materials (e.g. roller-compacted concrete , gabions ) and design techniques (e.g. embankment overtopping protection). The steps produce considerable energy dissipation along the chute and reduce the size of the required downstream energy dissipation basin. Research is still active on the topic, with newer developments on embankment dam overflow protection systems, converging spillways and small weir design. A bell-mouth spillway

3024-474: The water rises above the lip or crest of the spillway, it begins to be released from the reservoir. The rate of discharge is controlled only by the height of water above the reservoir's spillway. The fraction of storage volume in the reservoir above the spillway crest can only be used for the temporary storage of floodwater; it cannot be used as water supply storage because it sits higher than the dam can retain it. In an intermediate type, normal level regulation of

3080-695: The world is at Hungry Horse Dam in Montana, U.S., and is controlled by a 64-by-12-foot (19.5 by 3.7 m) ring gate. The bell-mouth spillway in Covão dos Conchos reservoir in Portugal is constructed to look like a natural formation. The largest bell-mouth spillway is in Geehi Dam , in New South Wales, Australia, measuring 105 ft (32 m) in diameter at the lake's surface. A siphon uses

3136-400: Was installed at the site of the former Reservoir keeper's house with a Speece cone installed at the bottom of the lake between that location and Alva canyon. Following the 2017 Oroville Dam crisis , the state of California conducted spillway inspections on all dams in the state. Hodges Dam did not pass inspection and, as a result, San Diego Public Utilities Department was ordered to keep

#574425