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Alluvial Fan Flooding (1996)

Chapter: A Characteristics and Hazards Reported in Published and Unpublished Accounts of Alluvial Fan Flooding

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Suggested Citation:"A Characteristics and Hazards Reported in Published and Unpublished Accounts of Alluvial Fan Flooding." National Research Council. 1996. Alluvial Fan Flooding. Washington, DC: The National Academies Press. doi: 10.17226/5364.
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Appendix A
Characteristics and Hazards Reported in Published and Unpublished Accounts of Alluvial Fan Flooding

Suggested Citation:"A Characteristics and Hazards Reported in Published and Unpublished Accounts of Alluvial Fan Flooding." National Research Council. 1996. Alluvial Fan Flooding. Washington, DC: The National Academies Press. doi: 10.17226/5364.
×

Fan(s)/Location

Hazard(s)a

Reference

Comments

Carefree fan Carefree, Arizona

4,5,8,10

Hjalmarson, 1994b

Storm of October 6, 1993, produced runoff in all of the trenched distributary channels on the alluvial fan. Measurements and estimates of peak discharge show that a significant part of the peak discharge at the fan toe was from runoff on the developed soils of the fan itself. Distributary channels typically were filled to less than about 1/2 of bankfull capacity. Coarse sand deposited along channel beds by previous floods was remobilized and transported further toward and past the fan toe. The Carefree alluvial fan is on a piedmont, and the drainage basin heads on a pediment.

Chicago Creek Hazelton, British Columbia, Canada

1,3,4,5,7,9, 10

Gottesfeld, Mathewes, Gottesfeld, 1991

Major debris flow about 3580 BP covered about 300 ha with deposited debris. The flow was two to three orders of magnitude larger than other historic debris flows. This catastrophic event that formed part of the alluvial fan may be one of the oldest oral records of a major debris flow in North America. The Gitksan people of the area still talk about this debris flow. Major Holocene and historic flows are evident at the mouth of Chicago Creek, a tributary to the Skeena River, in northern British Columbia, Canada. Dating of catastrophic postglacial debris flow deposits indicates 5 major flows during the past 10,000 years, or a recurrence interval of about 2,000 years.

Cottonwood Canyon Bishop, California

1–5,7,9,10

Beaty, 1963

Rare account from eyewitness of debris and mudflows on July 26, 1952. Two hours after a heavy thunderstorm in the White Mountains to the east, a large flow of debris advanced down the alluvial fan. At and below the apex the flow was in a pre-existent defined channel leading from the 9.5-km2 basin. Debris spilled over channel walls and spread laterally to widths of 30 to 120 m. One large distributary channel of debris was formed by concentrated overflow on the outside of a gradual bend. The debris deposit was about 6.9 km long with a deposit of mud 1.1 km long followed by 20 to 25 cm of silt deposits for at least 0.8 km near the fan toe above Benton, Washington. Much of the deposited debris was remobilized by subsequent water flow during the event.

Cottonwood Creek Boise, Idaho

3,8,10

Waananen, Harris, Williams, 1971

Flooding of January 1965 caused local flooding and much sediment deposition in downtown Boise, Idaho. Estimated sediment yield from the 31.1-km2 basin was about 38 metric tons per hectare.

 

3,8,10

Wyle, 1995c, Committee, 1995d

A wildfire burned much of vegetation in basin in 1959. Flood of August 20, 1959, deposited much sediment on fan. The unusual amount of sediment deposited by 1965 flood may be related to large amount of available sediment stored in basin tributaries

Suggested Citation:"A Characteristics and Hazards Reported in Published and Unpublished Accounts of Alluvial Fan Flooding." National Research Council. 1996. Alluvial Fan Flooding. Washington, DC: The National Academies Press. doi: 10.17226/5364.
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Comments

 

 

 

as a result of the wildfire in 1959. Considerably less sediment was deposited below the apexes of the Stuart and Crane Gulch alluvial fans a few miles to the west of the wildfire. The wildfire apparently destabilized the sediment production of an otherwise relatively stable (in an engineering context) drainage basin. The alluvial fans of Cottonwood Creek and Stuart and Crane Gulches are highly urbanized, and the paths of floodwater are significantly controlled by the conveyance capacity of the many streets that cross the fans at various angles relative to the general direction of fan slope.

Cucamonga Cucamonga, CA

3,4,6,8

Eckis, 1928

During the flood of February 16, 1927, small channels filled with debris and lessened the grade behind deposited debris, and spread floodwater to one or both sides of the debris dams. The spreading of floodwater and debris on the fans in the area, prior to the construction of the several flow control structures, is attributed to the many similar debris dams across channels.

 

3,4,8

Singer and McGlone, 1971

Flood inundation maps for the flood of January 25, 1969, show a wide area of inundation below the apex above a flood control dam. Heavy rainfall from January 18 to 25 produced record flooding at Cucamonga Creek. The peak discharge from the 26.2-km2 basin above the U.S. Geological Survey streamflow gage near Upland (number 11073470) was 399 km3/s, or nearly 1.4 times the previous record flood of 1938. The peak discharge decreased downstream as floodwater was stored in the many percolation basins on the coarse-permeable material of the alluvial fan. Approximately 5.2 km2 of fan area were inundated, mostly behind the percolation dams.

 

8

DMA, 1985

Flow paths are confined by the high banks in the upper fan. Flow paths are relatively stable except for areas affected by structures developed after 1938.

 

 

Committee, 1995d

Aerial photographs of August 3, 1989, reveal nearly all flow paths are affected by structures and floodwater is contained in structures. The compound fan has a large, deep trench in the old fan deposits on the south slopes of the San Gabriel Mountains. The region is geologically complex with marked differences among fans that form a bajada between the mountains and the Santa Ana River to the south. The Sierra Madre fault with a differential vertical movement of 1200 to 1500 m. forms the contact between the rugged mountains and steep piedmont (Eckis, 1928, p. 226). The hydrographic apex of the younger Cucamonga Fan cannot be precisely defined

Suggested Citation:"A Characteristics and Hazards Reported in Published and Unpublished Accounts of Alluvial Fan Flooding." National Research Council. 1996. Alluvial Fan Flooding. Washington, DC: The National Academies Press. doi: 10.17226/5364.
×

Fan(s)/Location

Hazard(s)a

Reference

Comments

 

 

 

because many detention dam-type percolation basins have been constructed in the trench and fan and the mid and lower fan is extensively urbanized. The hydrographic apex may be from about 0.8 to about 2.4 km below the mountain front, where there is little channel incision. The old trench is about 27 m deep and 270 m wide near the mountain front, about 9 to 12 m deep and 340 m wide 900 m below where it expands to a width of 760 m with an average depth of about 1.5 m 2,100 m below the mountain front.

Day and Deer creeks Etiwanda, CA

3,4,5,

Waanamen, 1969

Floodflows of January 25, 1969, discharged onto the alluvial fans, which coalesced and overflowed through residential areas. The peak discharge of 268 m3/s at the U.S. Geological Survey streamflow gaging station on Day Creek near Etiwanda, California (no. 11067000) was greater than the 100-year flood.

 

3,4

Singer and McGlone, 1971

Flood inundation maps show extensive flooding in the coalescing systems of distributary channels in the upper fan areas. Floodwaters of the two fans coalesced about 0.2 km below the mountain front. At the time of the flooding, there was a levee along the upper west side of the Deer Creek fan to divert flow to the east toward Day Creek. There also were two constructed flood channels on the western part of the Day Creek fan where the present feeder channel directs the flow from the 12.0-km2 basin upslope. Floodflows of January 25, 1969, which were greater than the 100-year flood, exceeded the capacity of the levee and channels on both fans.

 

3,4,8

Committee, 1995d

The flow paths of the several distributary channels on the fans apparently did not move during the flooding of 1969. The flow paths were examined using aerial photography on February 2, 1953, and August 3, 1989 (U.S. Natural Resources Conservation Service, Salt Lake City, Utah) and in the flood map report by Singer and McGlone (1971). The active appearing channels of both fans are interlacing over a width of 0.8 to 1.6 km within 3.2 km of the mountain front. Major channels of the two fans combine about 1.6 km below the mountain front. The pre-and post-floodflow paths are surprisingly similar, especially for such a large volume of floodwater and the reported tremendous quantities of transported sediment (Waananen, A.O., 1969, p. 14). The alteration of the natural drainage system by the levee and flood channels had some effect on the flow paths, but breaching occurred where major channels were intersected. With the exception on some minor effect of the structures, no change of flow paths over the fans was gleaned from the photographs. Clearly, even with the extensive and interlacing network of distributary channels, the

Suggested Citation:"A Characteristics and Hazards Reported in Published and Unpublished Accounts of Alluvial Fan Flooding." National Research Council. 1996. Alluvial Fan Flooding. Washington, DC: The National Academies Press. doi: 10.17226/5364.
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Fan(s)/Location

Hazard(s)a

Reference

Comments

 

 

 

floodwater has followed the existing network of channels during the 36 years spanned by the photographs.

 

3,4,8

DMA, 1985

Also concluded the flood channels in the area are rather stable. Five sets of aerial photographs taken over the period 1935 to 1969 were examined, and only one small new channel appeared to have formed on the Day Creek fan during the large flood of 1938. Except for the areas affected by the levees and channels constructed after the flood of March 2, 1938, no change in the channel pattern was detected.

Devil Canyon San Bernardino, California

4,8

DMA, 1985

Aerial photographs of distributary channels taken shortly before and after the second largest flood of record on March 2, 1938 show no movement of flow paths.

 

 

Commitee 1995d

The flow paths on the alluvial fan are significantly altered by construction of recharge basins and a flood channel that conveys floodwater past the fan.

Furnace Creek Death Valley, California

1,2,4,5,9

Crippen, 1979

Flood hazard area estimated and mapped. Author mentions the ''random" appearance of debris paths in upper very active portion of the fan.

 

1,2,10

Miller, 1997

Account of July 1968 flood.

 

1,3,4,5,9,10

Anstey, 1965

Flow of July 25, 1950, spread at apex and was lost to infiltration with deposited debris the result. Gorge near Furnace Creek Inn filled to a depth of 7.6 m. Gravel and rock rubble were deposited 3.2 km below apex.

 

3,5,10

Hunt and Mabey, 1966

Probable flow of July 25, 1950, eroded about 30 percent of small 25 year-old earth embankments on fan. Also eroded about 15 percent to 29 percent of tributary wash crossings on 50 year-old trails in basin. Veneer of recent clay in places on upper fan. Flood boundaries are clearly defined by new erosion or deposition.

Glendora, California

1,3,8,10

Geisner and Price, 1971

Flood inundation maps show flooding of urban area on small fan. Flow paths were significantly influenced by street pattern that was about parallel and perpendicular to the fan axis.

Glenwood Springs Glenwood Springs, Colorado

3,4,9,10

Mock and Pawlak, 1983

Map of alluvial fans and debris flows of storm of July 24, 1977, which inundated about 0.8 km2 of city with debris deposits. The city, which is located in western Colorado at 1,770-m elevation, is built on several alluvial fans that are active. Debris

Suggested Citation:"A Characteristics and Hazards Reported in Published and Unpublished Accounts of Alluvial Fan Flooding." National Research Council. 1996. Alluvial Fan Flooding. Washington, DC: The National Academies Press. doi: 10.17226/5364.
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Fan(s)/Location

Hazard(s)a

Reference

Comments

 

 

 

flows are generated by soil slumps usually in colluvium and move at velocities from 0.3 to 12 m/s. The city experiences a debris flow about once every 4 years (since 1903). There are at least 32 streams that drain the steep surrounding slopes that have produced debris flows. The storm of July 24, 1977, produced debris flows from 20 tributary streams to the Roaring Fork River and the Colorado River.

Hanapah Canyon Death Valley, California

1,4,5,8

Hooke, 1995e

Personal eyewitness account of January 1969 flooding. Flow in many distributaries. Velocities of 5.5 and 7.7 m/s measured with the use of surface flouts in channel visually estimated to be 3.5 m wide and 0.4 m deep.

 

4,5,8,9

Committee, 1995d

An excellent example of a fully trenched alluvial fan with shifting of the hydrographic apex far below the topographic apex. Large portions of the fan (the relict parts of the fan) are not subject to alluvial fan flooding. Numerous debris flow deposits with rounded lobes on the active portion of the fan.

Henderson Canyon Borrego Springs, CA

3,4,10

San Diego County, 1977; Committee, 1995d

Peak discharge on August 17, 1977, was 93.5 m3/s from the 16.3-km2 basin and upper fan. The hydrographic apex of the active alluvial fan is located on the lower south side of the relict fan, and floodflow split into two channels below the apex. Flow fanned out and became sheetflow below the hydrographic apex, and fine sediment was deposited over a large area. The young active fan is on the right or south side of the relict fan that was formed by debris flow deposits. Incision of stable channels in the older boulder deposits has shifted the apex of active deposition.

Horseshoe Park Estes Park, Colorado

1,2,3,5,10

Tunbridge, 1983

An earth dam broke on July 15, 1982, in Rocky Mountain National Park, producing a 6- to 10-m-high wall of water and debris in the Roaring River. In just a few hours an alluvial fan covering 70 ha was formed in a valley at the mouth of the river 10 km below the dam. Much of the material that formed the fan was from incision in the glacial till along the river. The "instant" fan was up to 10 m thick.

 

1–5,9,10

Blair, 1987

Peak water discharge at the fan was 340 m3/s based on dambreak model calibrated to eyewitness accounts. Released volume from dam of 830,000 m3. Eyewitness account at fan of leading edge of water, logs, and tree limbs followed by the flood peak 25 minutes later. Aerial photograph taken 5 hours after the flood arrived showed most of the fan had been formed. Most of fan building was from expanding sheetflooding that occurred in three phases. Some deposition was by supercritical flow on the flood recession. Following the major discharge the flood deposit was modified by erosion and redeposition of the sheetflood deposits.

Suggested Citation:"A Characteristics and Hazards Reported in Published and Unpublished Accounts of Alluvial Fan Flooding." National Research Council. 1996. Alluvial Fan Flooding. Washington, DC: The National Academies Press. doi: 10.17226/5364.
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Fan(s)/Location

Hazard(s)a

Reference

Comments

Howgill Fells Northwest England

3–10

Wells and Harvey, 1987

Storm of June 1982 destabilized hillslopes and produced both debris flows and water floods from a group of small basins. Thirteen fans with widely different physical characteristics were formed at tributary junctions. The new fans were up to 3 m thick and 100 m across. Fan processes were related to intrinsic fan-basin differences and to extrinsic characteristics such as sheep overgrazing by the Vikings in the 10th century. The 2.5-hour storm, with a recurrence interval of at least 100 years, produced extensive overland flow according to an eyewitness.

Lone Tree Creek Bishop, California

1–4,5,9,10

Beaty, 1963

See Cottonwood and Millner Canyons. The debris flow split near the mountain front forming an arm of debris deposits. Below the split the flow widened from 60 m to 150 m followed by mud and silt deposits similar to those at Cottonwood and Millner Canyons.

Lytle Creek San Bernardino, California

4,5,8

DMA, 1985

Largest two floods since 1920 were confined to defined channels between the mountain front and confluence with Cajon Creek. Based on comparison of aerial photographs taken shortly before and after floods of March 2, 1938, and January 25, 1969.

 

5,8

McGlashan and Ebert, 1918

Bank erosion is suggested in account of bridge failure.

 

4,8

Troxell, 1942

Bank erosion suggested during 1938 flood. Overbank flow near the Santa Anna River reported for great flood of 1861–62.

 

8

Eckis, 1928

Description of channel below the apex suggests the channel is the same as present (1996) channel.

 

1,4,5,8

Committee, 1995d

Based on comparison of aerial photographs of 1967 and 1989, flow paths are unchanged. The developed Soboba soils (NRCS, 1980) adjacent to the channel suggest the flow paths are stable. Channel capacity below the apex is about three times the magnitude of the largest flood of record since 1920 (U.S. Geological Survey gage no. 11062000).

Suggested Citation:"A Characteristics and Hazards Reported in Published and Unpublished Accounts of Alluvial Fan Flooding." National Research Council. 1996. Alluvial Fan Flooding. Washington, DC: The National Academies Press. doi: 10.17226/5364.
×

Fan(s)/Location

Hazard(s)a

Reference

Comments

Magnesia Spring Canyon Rancho Mirage, California

1–5,7,10

FEMA, 1989; Committee, 1995d

Major flood of July 1979 breached the levee at the apex and flooded urban development in the city of Rancho Mirage. The estimated peak discharge of the flood was 170 m3/s (Anderson-Nichols and Co.) from the 10.7-km2 mountainous drainage basin, or nearly 3 times the magnitude of the 100-year flood (Thomas, Hjalmarson, and Waltemeyer, 1994). One death and $7 million in damage resulted. The effect of the breached levee on the distribution of flow in the several distributary channels is difficult to assess, but, based on comparison of aerial photographs for 1955 and 1982, the floodflow followed the pre-levee channel network, while some floodflow may have been directed from the right side of the fan to an existing large, incised channel on the left. Under natural conditions the flood hazard of this alluvial fan may be especially severe because the 2.6-km2 fan area is relatively small for the drainage basin area. The peak discharge intensity, discharge per unit fan area, of the fan is fairly large, mostly because the fan is kept small as deposited material is periodically removed by Whitewater River, which forms the fan toe. A major flood and debris control structure has been constructed at the topographic apex.

Millner Canyon Bishop, California

1–5,9,10

Beaty, 1963

See Cottonwood Canyon. Large debris flow from the 26.2-km2 basin deposited debris within and adjacent to the defined front where the flow split into three distributary channels. The debris overtopped the walls of the distributary channels for another 2 miles, covering a total width of about 0.8 km as observed by an eyewitness. Like the Cottonwood Canyon fan, there were mudflow deposits below the debris deposits followed by silt deposits.

 

3,4,7,9,10

Beaty, 1970

The 1952 deposits and older deposits clearly described. The estimated recurrence interval of fan building events like the 1952 flood was 350 years.

 

3,4,7,9,10

Beaty, 1989

Major debris flows can be expected at intervals of a few hundred years. The recurrence interval for Millner Canyon fan was 320 years based on C-14 dating.

Montrose

1–5,7,10

Chawner, 1935

Abnormally large volumes of sediment and floodflow were produced from a recently burned basin during storm of December 31, 1933, and January 1, 1934. A 4.6-m wall of water carrying houses, trees, boulders, and people was reported. The deposited sediment on the alluvial fan was equivalent to a 0.02-m layer from the 7.8-km2 basin.

Suggested Citation:"A Characteristics and Hazards Reported in Published and Unpublished Accounts of Alluvial Fan Flooding." National Research Council. 1996. Alluvial Fan Flooding. Washington, DC: The National Academies Press. doi: 10.17226/5364.
×

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Reference

Comments

Northumberland Canyon Austin, Nevada

3,4

DMA, 1985

Flow paths depicted on aerial photograph of June 19, 1981 suggest flood of August 7, 1979 of 217 m3/s was confined in channel 4.42 km below the mountain front where a young fan has formed. Channel patterns on the fan suggest flow initially spread in several distributary channels and eventually became sheetflow.

 

1,3,4,7,10

Committee, 1995d

An approximately 0.8-km2 area of recent deposits and a larger area of older oxidized deposits form the active alluvial fan, which is inset in the older deposits of this compound fan. The most recent deposits probably are from the 1979 flood that was about 10 times the magnitude of the 100-year flood for the 41.3-km2 basin (Thomas, Hjalmarson, and Waltemeyer, 1994). The active alluvial fan is inset in the relict fan piedmont between the steep mountains to the east and salt marshes of a bolsom-like area to the west, which form much of the Big Smoky Valley. The large, deep trench in the relict deposits on the western slopes of the Toquima Mountain Range is incised for 4.4 km below the mountain front to the hydrographic apex. Trenching is restricted by a large bedrock outcrop 1.2 km below the mountain front. The cross section area of the trench is smaller but somewhat comparable in size to the trenches at the Cucamonga and Hanapah Canyon alluvial fans.

Picacho Peak Eloy, Arizona

4,6,9,10

Hjalmarson and Kemna, 1991

A small debris flow sometime between April and June 1989 followed the crest of alluvial fan in line with the channel axis at the fan apex. Deposited debris split 120 m below apex into two distinct lobes 60 and 45 m long. About 140 m3 of debris was deposited at average depths of 0.10 m with little, if any, water leaving the deposit bounds on the fan surface. The debris flow did not follow the axis of maximum slope below the topographic apex.

Saddle Mountain Arlington, AZ

1,3,4,6,8,10

USNRCS, 1987; Hjalmarson, 1995d

Major flood of September 2, 1984, filled and in places overflowed stable-trenched channels of relict fan. The peak discharge of the flood was 351 m3/s from the 22.3-km2 upper relict fan and steep mountainous drainage basin. A conveyance-slope estimate on a trenched-tributary stream draining a small mountainous basin suggests the unit discharge of 15.7 m3/s/km2 was nearly uniform over the mountains and upper piedmont, which are covered with varnished stones. Floodwater eroded several rills on the steep mountain slopes. Floodflow on the piedmont overtopped banks of stable distributary channels and inundated developed soils covered with varnished stones. A small amount of coarse material was deposited on varnished stones at one location where floodflow overtopped a relatively stable channel bank and spread over adjacent developed soils as sheetflow. No new distributary channels were formed. Floodwater

Suggested Citation:"A Characteristics and Hazards Reported in Published and Unpublished Accounts of Alluvial Fan Flooding." National Research Council. 1996. Alluvial Fan Flooding. Washington, DC: The National Academies Press. doi: 10.17226/5364.
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Fan(s)/Location

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Comments

 

 

 

at nearly bankfull depths was in all defined distributary channels with sheetflow on much of the developed soils of the relict fan. There was some erosion damage to the side inlets and upslope banks of the Saddleback floodwater diversion channel located across the lower portion of the relict fan (U.S. Natural Resources Conservation Service, 1987). Much of the flood damage to the diversion structure was the result of inadequately sized floodwater inlets or because inlets were not located on some of the deceptively small distributary channels, which can convey shallow floodflow at near-critical velocities.

San Fernando Valley Los Angeles, California

3,4

King et al., 1981

Both confined flow and sheetflow are shown on maps of several riverine and alluvial fan areas flooded during 1934 through 1956.

Santa Monica Creek Carpinteria, California

3,4,8

Fenzel and Price, 1971

Flood of January 1969 overtopped stream banks at apex of alluvial fan and moved overland in thin sheets. Map of flooded area shows that most of flooding was in an agricultural area.

Sydney fans Australia

3–8,9

Scott and Erskine, 1994

Storm of February 2–4, 1990, caused a variety of responses on 12 small fans including avulsions, progressive aggradation, localized erosion, and fanhead trench reworking. One fan experienced no detectable change, while 7 with trenches experienced trench reworking. Three fans had localized deposition, 2 had spatially disjunct erosion and deposition and/or channel avulsions. Avulsion was related to channel filling with a steeper alternate path leading from the newly formed topographic high to a topographic low. Although the 12 fans are very small and formed by water flood processes, a potentially significant result identified by the authors was a threshold slope for fanhead trench initiation.

Wadi Mikeimin Sinai Desert

1,3,7,9,10

Schick and Lekach, 1989

An alluvial fan was formed during the flood of January 1971 at the confluence of Wadi Mikeimin and Wadi Watir. The fan dammed Wadi Watir for 21 months before it was washed out by a major flood. The peak of 68.5 m3/s from the 13-km3 basin deposited 6,200 m3 of coarse predominantly stratified sediment. The total flow of the flood was in excess of 100,000 m3. The slope of the channel at the fan apex was 0.087.

Suggested Citation:"A Characteristics and Hazards Reported in Published and Unpublished Accounts of Alluvial Fan Flooding." National Research Council. 1996. Alluvial Fan Flooding. Washington, DC: The National Academies Press. doi: 10.17226/5364.
×

Fan(s)/Location

Hazard(s)a

Reference

Comments

Wasatch Front Salt Lake City, Utah

2,7,9,10

Patton and Baker, 1976

Between 1847 and 1938, over 500 cloudburst floods were recorded along the Wasatch mountain front with reports of damage. Although not specifically given, many, if not most, of these floods were on alluvial fans because of the great concentration of fans along the front. Between 1939 and 1969, accounts of 836 flash floods were reported, the majority of which were along the front. Flash floods commonly cause debris flows, which greatly increase property damage.

 

9,10

Mathewson and Keaton, 1990

Based on historic records of flood damage, the damaging debris flows during the springs of 1983 and 1984 may have a recurrence interval of 100 years if the type of initiating mechanism is considered irrelevant. However, only 3 to 5 prehistory debris flows have occurred during the past 12,000 years. Many large debris flows occurred in the 1920s and 1930s that were triggered by thunderstorms. At that time the slopes had been cleared of dense vegetation by burning to encourage new growth of grasses and improve grazing. The debris flows of the 1920s and 1930s were totally different from those of 1983 and 1984. Recurrence intervals (RI) of Davis County debris flows along the Wasatch mountain front are difficult to define as shown by the following: RI = 100 years based on historic record, RI = 3,000 years based on stratigraphic record, RI = 10,000 years based on phenomena causing the 1983 and 1984 flows.

White Tanks Phoenix, Arizona

1,3,4,5,7,10

Hjalmarson and Kemna, 1991

Active alluvial fan with evidence of recent channel movement within active fan boundaries probably as a result of frequent floods. Hydrologic apex is below trenched channel in relict deposits where there was no evidence of flow path movement. Also, no evidence of recent channel movement in lower portion of active alluvial fan where there has been little recent floodflow because floodwater of the common floods that passes the hydrographic apex is lost to infiltration.

 

1,3,4,5,7,10

CH2M HILL, 1992

Aerial photographs for 1942 through 1979 comparison shows that about 24 percent of the 35 km of channels shifted location or were formed. Paleoflood analysis indicates no major floods during this period.

Wild Burro Tucson, Arizona

3,4,5,8

Pearthree et al., 1995

Flood 1988 on the southern piedmont of the Tortolita Mountains followed distinct and existing flow paths separated by large dry areas. Floodflow of the rare flood (p < 0.01) split into 42 paths. Dry areas separating the flow were more than one half of the alluvial fan. Surfical geology and flood boundaries were mapped to produce a rare display of alluvial fan flooding on a system of trenched distributary channels.

Suggested Citation:"A Characteristics and Hazards Reported in Published and Unpublished Accounts of Alluvial Fan Flooding." National Research Council. 1996. Alluvial Fan Flooding. Washington, DC: The National Academies Press. doi: 10.17226/5364.
×

aReported flood characteristics and hazards:

1. High flow velocities

2. Flash floods and possibly translatory waves

3. Sheetflow and/or sheetflooding

4. Distributary-flow

5. Unstable channel boundaries including bed and bank erosion and remobilization of deposited sediment

6. Stable channel boundaries

7. Movement of flow paths

8. Stable flow paths

9. Debris flow (including hyperconcentrated and mudflows)

10. Alluviation

b Based on unpublished data and observations of H.W. Hjalmarson on file at the Flood Control District of Maricopa County, Arizona.

c Based on oral communication with Jim Wyle of City of Boise Idaho Public Works, April 14, 1995.

d Based largely on unpublished field observations made during the course of this study by one or more members of the Committee on Alluvial Fan Flooding.

e From unpublished observations and measurements in field notes for flood of January 1969.

Suggested Citation:"A Characteristics and Hazards Reported in Published and Unpublished Accounts of Alluvial Fan Flooding." National Research Council. 1996. Alluvial Fan Flooding. Washington, DC: The National Academies Press. doi: 10.17226/5364.
×

REFERENCES

Anderson-Nichols and Co. 1981. Floodplain Management Tools for Alluvial Fans. Federal Emergency Management Agency Contract EMW-C-0715.

Anstey, R. L. 1965. Physical Characteristics of Alluvial Fans: United States Army Natick Laboratory, Technical Report ES-20.


Beaty, C. B. 1963. Origin of alluvial fans, White Mountains, California and Nevada. Pp. 66–73 in Modern and Ancient Alluvial Fan Deposits, T. H. Nilsen, ed. New York: Van Nostrand Reinhold Co.

Beaty, C. B. 1970. Age and estimated rate of accumulation of an alluvial fan, White Mountains, California, U.S.A. American Journal of Science 268:50–77.

Beaty, C. B. 1989. Great big boulders I have known. Geology 17:349–352.

Blair, T. C. 1987. Sedimentary processes, vertical stratification sequences, and geomorphology of the Roaring River alluvial fan, Rocky Mountain National Park, Colorado. Journal of Sedimentary Petrology 57(1):1–18.


Chawner, W. D. 1935. Alluvial fan flooding the Montrose, California, flood of 1934: Geological Review, American Geographical Society of New York 25(2):255–263.

CH2M Hill. 1992. Alluvial fan data collection and monitoring study: On file at Flood Control District of Maricopa County, Arizona.

Crippen, J. R. 1979. Potential hazards from floodflows and debris movement in the Furnace Creek area, Death Valley National Monument, California-Nevada: U.S. Geological Survey Open-File Report 79-991. Reston, Va.: U.S. Geological Survey.


DMA Consulting Engineers. 1985. Alluvial Fan Flooding Methodology—An Analysis . Federal Emergency Management Agency Contract EMW-84-C-1488. Washington, D.C.: FEMA.


Eckis, R. 1928. Alluvial fans of the Cucamonga district, Southern California: Journal of Geology 36:224–247.


Federal Emergency Management Agency (FEMA). 1989. Alluvial Fans: Hazards and Management. FEMA Document 165. Washington, D.C.: FEMA.


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Suggested Citation:"A Characteristics and Hazards Reported in Published and Unpublished Accounts of Alluvial Fan Flooding." National Research Council. 1996. Alluvial Fan Flooding. Washington, DC: The National Academies Press. doi: 10.17226/5364.
×

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Suggested Citation:"A Characteristics and Hazards Reported in Published and Unpublished Accounts of Alluvial Fan Flooding." National Research Council. 1996. Alluvial Fan Flooding. Washington, DC: The National Academies Press. doi: 10.17226/5364.
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Alluvial fans are gently sloping, fan-shaped landforms common at the base of mountain ranges in arid and semiarid regions such as the American West. Floods on alluvial fans, although characterized by relatively shallow depths, strike with little if any warning, can travel at extremely high velocities, and can carry a tremendous amount of sediment and debris. Such flooding presents unique problems to federal and state planners in terms of quantifying flood hazards, predicting the magnitude at which those hazards can be expected at a particular location, and devising reliable mitigation strategies.

Alluvial Fan Flooding attempts to improve our capability to determine whether areas are subject to alluvial fan flooding and provides a practical perspective on how to make such a determination. The book presents criteria for determining whether an area is subject to flooding and provides examples of applying the definition and criteria to real situations in Arizona, California, New Mexico, Utah, and elsewhere. The volume also contains recommendations for the Federal Emergency Management Agency, which is primarily responsible for floodplain mapping, and for state and local decisionmakers involved in flood hazard reduction.

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