National Water Summary 1988-89--Floods and Droughts: WSP 3675

 

Prepared by S.D. Waltemeyer and R.L. Gold, U.S. Geological Survey; "General Climatology" section by K.E. Kunkel, State Climatologist

New Mexico

Floods and Droughts

New Mexico’s topography has a major effect on its climate.  Mountainous terrain, which extends from the northern to the central part of the State, combines with wind and moisture to produce diverse weather and climate. Principal moisture-delivery systems in New Mexico (fig. 1) vary seasonally in importance. Snowfall in the mountains is largely the result of midwinter storm systems from the Pacific Ocean. Intense rainfall during the summer is usually moisture from the Gulf of Mexico.

Regional thunderstorms develop over the mountains during early and late summer. Significant floods, such as the early summer flood of 1965 and the early fall flood of 1904, have occurred during these times. However, the greatest monthly precipitation, although mostly of irregular regional extent, typically is received in July and August. Intense, convective midsummer storms commonly are preceded by mild rainfall, which saturates the ground and thus increases surface runoff. Melting of snowpack in the mountains may combine with spring rainfall to produce severe flooding, particularly in the northern part of the State.

The State was affected by major droughts during 1931–41 and 1942–79. The duration, areal extent, and severity of these events were determined from streamflow records collected at gaging stations on the State’s rivers and streams. The droughts affected the entire State; however, their severity varied both areally and temporally.

Management of New Mexico’s water resources during floods and droughts is shared by Federal, State, and local agencies. The New Mexico State Engineer Office, the U.S. Bureau of Reclamation, and the U.S. Army Corps of Engineers cooperate to transfer water among the State’s reservoirs during floods and droughts. Flood-plain insurance activities are directed, in part, by the Federal Emergency Management Agency. The National Weather Service provides flood-warning information.

GENERAL CLIMATOLOGY

New Mexico is in a subtropical region that has meager precipitation statewide. Average annual precipitation ranges from about 7 inches in the northwest to about 20 inches in some mountains. The statewide average annual precipitation is about 14 inches.

The local topography significantly modifies New Mexico’s regional weather and climate. Mountain ranges, which trend generally northward, are barriers to the prevailing westerly winds in the winter. The mountains force low-level air to rise and cause an orographic effect along the mountain slopes. As the air cools, condensation and precipitation result if sufficient moisture is present. Consequently, in the winter, more precipitation (mostly snow) falls on the mountains than on the surrounding valleys and plains. The topography also affects the spatial distribution of precipitation in the summer. Because of the uneven land surface, daytime heating of air generates thermal instability above the mountains more quickly than above the surrounding valleys and plains. Thus, convective ­showers are most common over the mountains.

During the summer, the principal source of moisture for the entire State is the Gulf of Mexico. The gulf also is a significant source of year-round moisture for the eastern plains of New Mexico. Precipitation occurs primarily from scattered thunderstorms that are produced by daytime heat. The areal coverage and intensity of these systems can ­increase as a result of tropical disturbances. Rarely, the remnants of tropical cyclones from the Gulf of Mexico or Pacific Ocean move across the State. Tropical cyclones, which include tropical storms and hurricanes, dissipate either over the ocean or in coastal areas of other States, and the residual moisture is transported into New Mexico.

During the fall, precipitation can occur when southward-moving frontal systems interact with residual moisture originating in the Gulf of Mexico, particularly in the eastern plains and central mountains. The principal moisture from late fall to early spring originates in the Pacific Ocean and affects the western part of the State. Pacific moisture also contributes to precipitation in the eastern plains, although the Pacific is not as important a source as the Gulf of Mexico. Occasionally, the remnants of an eastern Pacific tropical cyclone bring locally intense rain in the fall.

During the winter, the circumpolar jetstream is north of New Mexico and the weather usually is clear and mild. Ocassionally ­however, the jetstream dips southward over the State and the weather becomes cooler. Then the potential for substantial precipitation is increased particularly in the mountains. By late spring, the cir­cumpolar jetstream has moved well to the north of New Mexico. From late spring through early summer a subtropical high-pressure system generally predominates. The result is warm to hot weather and little precipitation. Precipitation in the winter and early spring in the western part of the State usually is produced by storms from the ­Pacific. The eastern plains may receive significant snowfall from arctic cold fronts moving southward. By late spring, moisture from the Gulf of Mexico can extend to the eastern border of New Mexico. Eastward-moving frontal systems interact with this moisture to produce thunderstorms that produce hail and even tornadoes, particularly in May. As summer progresses, the Bermuda High, a high-pressure system over the ­Atlantic Ocean, causes low-level winds to shift from the west and southwest to the south and southeast and carry moisture from the Gulf of Mexico. The arrival of this moisture signals the beginning of the summer rainy season. Statewide, July and August generally are the wettest months.

In addition to the oceans, important moisture sources include local and upwind land surfaces, as well as lakes and reservoirs, from which moisture evaporates into the atmosphere.  Typically, as a moisture-laden ocean airmass moves inland, it is modified to include some water that has been recycled one or more times through the land-vegetation-air interface.

The origin of individual floods in New Mexico depends on the local topography and the moisture source. Some mountain valleys are susceptible to spring snowmelt flooding; however, the system of dams and reservoirs on New Mexico rivers alleviates this threat for most of the State. During late spring and summer, isolated, intense, slow-moving thunderstorms occasionally cause local flooding. Also, tropical disturbances sometimes dominate a region during late spring and late summer, and cause widespread rainfall that can last for several days. In the fall and winter, frontal systems from the Pacific Ocean cause flooding if sufficient moisture is transported into the State from the southwest. The orographic effect caused by the southwestern mountains generally produces extreme precipitation and runoff, which sometimes give rise to flooding and property damage.

MAJOR FLOODS AND DROUGHTS

The most significant floods and droughts in New Mexico are listed chronologically in table 1; rivers and cities are shown in figure 2. The floods listed are those having recurrence intervals greater than 25 years; the droughts listed are those having recurrence intervals greater than 10 years. Records from 53 streamflow-gaging stations were used to determine the duration, areal extent, and severity of floods; records from 17 gaging stations were used to determine the same characteristics for droughts. Streamflow data are collected, stored, and reported by water year (a water year is the 12-month period from October 1 through September 30 and is identified by the calendar year in which it ends).

From the gaging stations studied, six were selected to depict floods (fig. 3) and six were selected to depict droughts (fig. 4); three of the gaging stations were used for both analyses. The gaging stations are located on largely unregulated streams and were selected on the basis of areal distribution, diversity of basin size, and hydrologic setting. The existence of substantial regulation eliminated from consideration the following major rivers: the San Juan, Pecos, and Canadian Rivers and the Rio Grande. Long-term trends in periods of declining streamflows may be discerned from gaging-station records for the regulated streams, but individual droughts are difficult to define.

FLOODS

The areal extent and severity of major floods and the annual peak discharges at the selected gaging stations are shown in figure 3. Also shown on the peak-discharge hydrographs are the magnitudes of discharges having 10- and 100-year recurrence intervals.

Two large floods affecting the eastern part of the State were those of 1904 and June 17, 1965. In 1904, few gaging stations were in operation in New Mexico. Consequently, the period of record for the six gaging stations used to depict floods does not include the 1904 flood; however, other stations in operation recorded streamflow conditions during the 1904, 1941, 1942, and 1965 floods. Records from those stations indicate that the 1904 flood peak discharges generally were larger than those of the 1965 flood. Major damage was reported along the Pecos, Canadian, Cimarron, Red, Gallinas, Mora, Sapello, and Santa Fe Rivers; along Rayado and Manuelitas Creeks; and along the Rio Grande (Monk, 1904). Information from eyewitnesses provided a basis for determining flood damage, which was estimated to be at least $1 million; of this amount, one-half was damage to railroads (Monk, 1904).

The flood of September 23, 1941, affected mostly the central part of the State. On September 23, 1941, the peak discharge of the Rio Puerco near Bernardo (fig. 3, site 3) was 18,800 ft3/s (cubic feet per second). Peak discharges of most streams in the affected areas had recurrence intervals greater than 50 years. Other areas that had peak discharges with recurrence intervals of less than 50 years probably also were affected by the flood; however, records do not exist to document streamflow conditions.

The September 1, 1942, flood affected the central and eastern parts of the State and, to a lesser extent, the northeastern part. Streamflow records indicate that peak discharges at most gaging stations had recurrence intervals of 50–75 years. On September 1, 1942, the peak discharge of the Pecos River near Puerto de Luna
(fig. 3, site 4) was 48,600 ft3/s, which has a recurrence interval greater than 100 years. Accounts by local residents indicate that the 1942 flood was of lesser magnitude than the 1904 flood.

The flood of June 17, 1965, likewise was not as severe as the flood of 1904. There was no loss of human life, but property damage was estimated to be tens of millions of dollars (Snipes and others, 1974). Streamflow records indicate that the 1965 flood had a recurrence interval greater than 100 years in many areas across the eastern part of the State. For example, on June 17, 1965, the peak discharge of the Vermejo River near Dawson (fig. 3, site 1) was 12,600 ft3/s, the peak discharge of record for that gaging station. This flood occurred during a major drought but did not have an appreciable effect on the drought because of the relatively short duration of the increased streamflows.

In addition to the floods previously described, severe flooding occurred in parts of the State on October 6, 1911 (water year 1912), June 29, 1927, April 24, 1942, December 19, 1978 (water year 1979), and June 9, 1988. In those instances, however, flooding was localized and did not cause widespread damage. The peak discharge of the October 6, 1911, flood has remained undetermined. However, the peak stage of the Animas River at Farmington (fig. 3, site 5) during the 1911 flood was about twice the stage of the flood of June 29, 1927, which had a peak discharge of about 25,000 ft3/s. The recurrence interval for the flood of June 29, 1927, on the Animas and San Juan Rivers exceeded 100 years, as did that of the flood of April 24, 1942, on the Rio Grande in the central part of the State. Major flooding on the Gila River near Redrock (fig. 3, site 6) on December 19, 1978, resulted in a peak discharge of 48,800 ft3/s. The flood of June 9, 1988, on the Vermejo River near Dawson (fig. 3, site 1) had a peak discharge of about 10,400 ft3/s. Floods of both the Gila River near Redrock on December 19, 1978, and the Vermejo River near Dawson on June 9, 1988, had recurrence intervals between 75 and 100 years.

DROUGHTS

Droughts are common in New Mexico. The normally meager annual precipitation causes extended periods of scant flow in the State’s unregulated rivers. Streamflow records can be used as one means to determine the duration and areal extent of droughts.

The duration, areal extent, and severity of major droughts in New Mexico are shown in figure 4. The areas of drought delineated on the maps are based on data from the six gaging stations shown in the figure and from other gaging stations statewide. However, only the gaging stations shown are used to describe the general severity of droughts.

The annual departure from average stream discharge for any year is the difference between the average discharge for that year, which is determined from daily streamflow records, and the average discharge for the period of record. Annual departures for the six selected gaging stations are shown in figure 4. A bar above the zero line is a positive departure from normal, and a bar below the zero line is a negative departure from normal. An extended period of negative departures indicates a hydrologic drought. Records for some gaging stations indicate an almost continuous deficiency of streamflow throughout a given drought, whereas records for other stations may indicate 1 or more years when streamflow was average or greater than average during a drought.

Such short-term reversals in trend can indicate two separate droughts or a short recovery period within the major drought. A study that employed a 5-year moving average to analyze streamflow within the Rio Grande basin showed that such reversals did not constitute recovery periods (Waltemeyer, 1987). Therefore, in this study, streamflow deficiencies were computed for each drought within the longer drought period to determine a recurrence interval.

Major long-term droughts occurred in New Mexico during 1931–41 and 1942–79. The duration of the two droughts differed among streamflow-gaging stations, and the dates represent the earliest beginning date and latest ending date common to most stations. For example, at five of the six gaging stations, the 1942–79 drought ended in 1979, but the start of the drought ranged from 1942 to 1948. Most gaging-station records from the statewide network indicate a sustained drought from 1950 to 1979.

The drought of 1931–41 affected the entire State. The Dust Bowl conditions in the Plains States probably are the most memorable aspect of this drought. Streamflow deficiencies in New Mexico during this period were significant but less severe than those during the subsequent drought. Streamflow records for the Vermejo River near Dawson (fig. 4, site 1), Rio Hondo near Valdez (fig. 4, site 3), and Pecos River near Pecos (fig. 4, site 4) indicate that the drought had recurrence intervals of 10–25 years in north-central New Mexico. In most of the State, however, the drought was severe and had a recurrence interval greater than 25 years. Nevertheless, no annual precipitation minimums were recorded at any weather station in the vicinity of the gaging stations during the 1931–41 drought.

An extended period of deficient streamflow affecting all of New Mexico lasted from the early 1940’s to late 1970’s (fig. 4). The 1942–79 drought greatly affected nonirrigated agricultural areas in New Mexico. Although farmers in the State have minimized the effect of drought on their crops by irrigating, dryland farming is still practiced for some crops, such as wheat. Wheat production in the 1950’s was the smallest since 1909 (Cockril, 1959). By the end of the 1950’s, about 2,000 wells had been drilled to supplement surface-water irrigation allotments, which had been decreased in response to the drought (Wayne Cunningham, Elephant Butte Irrigation District, oral commun., 1988). Precipitation records indicate the severity of the 1942–79 drought:  annual precipitation minimums were recorded at Albuquerque (4.06 inches in 1956), Farmington (4.07 inches in 1950), Carlsbad (4.40 inches in 1956), and Glenwood (6.90 inches in 1956) (Kunkel, 1984).

During the drought, streamflow deficiencies were recorded at all six gaging stations, and periods of greater than average annual departures generally did not exceed about 2 years. At Ute Creek near Logan (fig. 4, site 2), however, periods in which sustained streamflow deficiencies exceeded surpluses did not begin until 1961.

WATER MANAGEMENT

Federal, State, and local government agencies, acting on the authority of various statutes, are responsible for flood-plain management, flood-warning systems, and water-use management during drought. Historical records of streamflow provide much of the basis for New Mexico’s management of surface water during floods and droughts.

Flood-Plain Management.—The New Mexico State Engineer Office coordinates the National Flood Insurance Program, and the Federal Emergency Management Agency administers the program for participating counties. Insurance needs in special flood-hazard areas were met by the National Flood Insurance Act of 1968. The National Flood Disaster Protection Act of 1973 expanded the availability of insurance to other areas but imposed flood-plain management activities on property owners and communities. In addition, the Flood Control Act (P.L. 93–234) authorized the U.S. Army Corps of Engineers to provide flood-plain studies. These studies are similar to those conducted under the authority of the National Flood Insurance Program and are performed under the authority of the Federal Emergency Management Agency.

Flood-Warning Systems.—In conjunction with the U.S. Bureau of Reclamation, the U.S. Army Corps of Engineers operates multiple-purpose reservoirs throughout the State to provide water storage during floods. State statutes provide the State Engineer with authority to administer dam safety programs that provide for adequate design inflow and seismic stability. Flood-warning activities in the State are provided under the direction of the River Forecast Center of the National Weather Service. This flood-warning system issues current rainfall and streamflow data for strategic points statewide that can be used to alert reservoir managers in the event of a flood.

Water-Use Management During Droughts.—Most small streams in the State, excluding those in mountainous areas, are ephemeral. In contrast, the larger perennial streams have become water-transmission systems because of the construction of reservoirs. These reservoirs were designed and are operated, in part, to decrease streamflow variability and to ensure water supply for a multitude of purposes. State and Federal agencies determine who receives the water and in what quantities. The agencies acquire their authority from interstate compacts and State laws enacted through many years. The result is a system that minimizes the effect of droughts. For example, the agriculture industry, which is the largest user of surface and ground water in the State, minimizes the effect of drought on crop production through irrigation. In recent years the major controversy concerning water supply has been the overabundance of water within the water-distribution network (Hester, 1987).

SELECTED REFERENCES

Cockril, P.W., 1959, A statistical history of crop and livestock production in New Mexico: New Mexico State University, New Mexico Agricultural Experiment Station Bulletin 438, 35 p.

Hester, Nolan, 1987, Who are the outsiders?, in Harris, L.G., ed., Managing the river: Las Cruces, New Mexico, 31st Annual New Mexico Water Conference, Water Resources Research Institute, Proceedings, 264 p.

Kunkel, K.E., 1984, Temperature and precipitation summaries for selected New Mexico locations: New Mexico Department of Agriculture, Climate Report, 190 p.

Monk, G.B., 1904, Report of floods in New Mexico during September and October 1904: U.S. Geological Survey files, 25 p.

Snipes, R.J., and others, 1974, Floods of June 1965 in Arkansas River basin, Colorado, Kansas, and New Mexico: U.S. Geological Survey Water-Supply Paper 1850–D, 97 p.

U.S. Geological Survey, 1973, Hydrologic unit map of New Mexico: U.S. Geological Survey Hydrologic Unit Map, scale 1:500,000.

______1976–87, Water resources data for New Mexico, water years 1975–86: U.S. Geological Survey Water-Resources Data Reports NM–75–1 to NM–86–1, published annually.

______1986, National water summary 1985—Hydrologic events and surface-water resources: U.S. Geological Survey Water-Supply Paper 2300, 506 p.

______1990, National water summary 1987—Hydrologic events and water supply and use: U.S. Geological Survey Water-Supply Paper 2350, 553 p.

Waltemeyer, S.D., 1986, Techniques for estimating flood-flow frequency for unregulated streams in New Mexico: U.S. Geological Survey Water-Resources Investigations Report 86–4104, 56 p.

______1987, Trends in streamflow and reservoir contents in the Rio Grande basin, New Mexico: Las Cruces, 31st Annual New Mexico Water Conference, Water Resources Research Institute, Proceedings, 264 p.

New Mexico’s topography has a major effect on its climate.  Mountainous terrain, which extends from the northern to the central part of the State, combines with wind and moisture to produce diverse weather and climate. Principal moisture-delivery systems in New Mexico (fig. 1) vary seasonally in importance. Snowfall in the mountains is largely the result of midwinter storm systems from the Pacific Ocean. Intense rainfall during the summer is usually moisture from the Gulf of Mexico.

Regional thunderstorms develop over the mountains during early and late summer. Significant floods, such as the early summer flood of 1965 and the early fall flood of 1904, have occurred during these times. However, the greatest monthly precipitation, although mostly of irregular regional extent, typically is received in July and August. Intense, convective midsummer storms commonly are preceded by mild rainfall, which saturates the ground and thus increases surface runoff. Melting of snowpack in the mountains may combine with spring rainfall to produce severe flooding, particularly in the northern part of the State.

The State was affected by major droughts during 1931–41 and 1942–79. The duration, areal extent, and severity of these events were determined from streamflow records collected at gaging stations on the State’s rivers and streams. The droughts affected the entire State; however, their severity varied both areally and temporally.

Management of New Mexico’s water resources during floods and droughts is shared by Federal, State, and local agencies. The New Mexico State Engineer Office, the U.S. Bureau of Reclamation, and the U.S. Army Corps of Engineers cooperate to transfer water among the State’s reservoirs during floods and droughts. Flood-plain insurance activities are directed, in part, by the Federal Emergency Management Agency. The National Weather Service provides flood-warning information.

GENERAL CLIMATOLOGY

New Mexico is in a subtropical region that has meager precipitation statewide. Average annual precipitation ranges from about 7 inches in the northwest to about 20 inches in some mountains. The statewide average annual precipitation is about 14 inches.

The local topography significantly modifies New Mexico’s regional weather and climate. Mountain ranges, which trend generally northward, are barriers to the prevailing westerly winds in the winter. The mountains force low-level air to rise and cause an orographic effect along the mountain slopes. As the air cools, condensation and precipitation result if sufficient moisture is present. Consequently, in the winter, more precipitation (mostly snow) falls on the mountains than on the surrounding valleys and plains. The topography also affects the spatial distribution of precipitation in the summer. Because of the uneven land surface, daytime heating of air generates thermal instability above the mountains more quickly than above the surrounding valleys and plains. Thus, convective ­showers are most common over the mountains.

During the summer, the principal source of moisture for the entire State is the Gulf of Mexico. The gulf also is a significant source of year-round moisture for the eastern plains of New Mexico. Precipitation occurs primarily from scattered thunderstorms that are produced by daytime heat. The areal coverage and intensity of these systems can ­increase as a result of tropical disturbances. Rarely, the remnants of tropical cyclones from the Gulf of Mexico or Pacific Ocean move across the State. Tropical cyclones, which include tropical storms and hurricanes, dissipate either over the ocean or in coastal areas of other States, and the residual moisture is transported into New Mexico.

During the fall, precipitation can occur when southward-moving frontal systems interact with residual moisture originating in the Gulf of Mexico, particularly in the eastern plains and central mountains. The principal moisture from late fall to early spring originates in the Pacific Ocean and affects the western part of the State. Pacific moisture also contributes to precipitation in the eastern plains, although the Pacific is not as important a source as the Gulf of Mexico. Occasionally, the remnants of an eastern Pacific tropical cyclone bring locally intense rain in the fall.

During the winter, the circumpolar jetstream is north of New Mexico and the weather usually is clear and mild. Ocassionally ­however, the jetstream dips southward over the State and the weather becomes cooler. Then the potential for substantial precipitation is increased particularly in the mountains. By late spring, the cir­cumpolar jetstream has moved well to the north of New Mexico. From late spring through early summer a subtropical high-pressure system generally predominates. The result is warm to hot weather and little precipitation. Precipitation in the winter and early spring in the western part of the State usually is produced by storms from the ­Pacific. The eastern plains may receive significant snowfall from arctic cold fronts moving southward. By late spring, moisture from the Gulf of Mexico can extend to the eastern border of New Mexico. Eastward-moving frontal systems interact with this moisture to produce thunderstorms that produce hail and even tornadoes, particularly in May. As summer progresses, the Bermuda High, a high-pressure system over the ­Atlantic Ocean, causes low-level winds to shift from the west and southwest to the south and southeast and carry moisture from the Gulf of Mexico. The arrival of this moisture signals the beginning of the summer rainy season. Statewide, July and August generally are the wettest months.

In addition to the oceans, important moisture sources include local and upwind land surfaces, as well as lakes and reservoirs, from which moisture evaporates into the atmosphere.  Typically, as a moisture-laden ocean airmass moves inland, it is modified to include some water that has been recycled one or more times through the land-vegetation-air interface.

The origin of individual floods in New Mexico depends on the local topography and the moisture source. Some mountain valleys are susceptible to spring snowmelt flooding; however, the system of dams and reservoirs on New Mexico rivers alleviates this threat for most of the State. During late spring and summer, isolated, intense, slow-moving thunderstorms occasionally cause local flooding. Also, tropical disturbances sometimes dominate a region during late spring and late summer, and cause widespread rainfall that can last for several days. In the fall and winter, frontal systems from the Pacific Ocean cause flooding if sufficient moisture is transported into the State from the southwest. The orographic effect caused by the southwestern mountains generally produces extreme precipitation and runoff, which sometimes give rise to flooding and property damage.

MAJOR FLOODS AND DROUGHTS

The most significant floods and droughts in New Mexico are listed chronologically in table 1; rivers and cities are shown in figure 2. The floods listed are those having recurrence intervals greater than 25 years; the droughts listed are those having recurrence intervals greater than 10 years. Records from 53 streamflow-gaging stations were used to determine the duration, areal extent, and severity of floods; records from 17 gaging stations were used to determine the same characteristics for droughts. Streamflow data are collected, stored, and reported by water year (a water year is the 12-month period from October 1 through September 30 and is identified by the calendar year in which it ends).

From the gaging stations studied, six were selected to depict floods (fig. 3) and six were selected to depict droughts (fig. 4); three of the gaging stations were used for both analyses. The gaging stations are located on largely unregulated streams and were selected on the basis of areal distribution, diversity of basin size, and hydrologic setting. The existence of substantial regulation eliminated from consideration the following major rivers: the San Juan, Pecos, and Canadian Rivers and the Rio Grande. Long-term trends in periods of declining streamflows may be discerned from gaging-station records for the regulated streams, but individual droughts are difficult to define.

FLOODS

The areal extent and severity of major floods and the annual peak discharges at the selected gaging stations are shown in figure 3. Also shown on the peak-discharge hydrographs are the magnitudes of discharges having 10- and 100-year recurrence intervals.

Two large floods affecting the eastern part of the State were those of 1904 and June 17, 1965. In 1904, few gaging stations were in operation in New Mexico. Consequently, the period of record for the six gaging stations used to depict floods does not include the 1904 flood; however, other stations in operation recorded streamflow conditions during the 1904, 1941, 1942, and 1965 floods. Records from those stations indicate that the 1904 flood peak discharges generally were larger than those of the 1965 flood. Major damage was reported along the Pecos, Canadian, Cimarron, Red, Gallinas, Mora, Sapello, and Santa Fe Rivers; along Rayado and Manuelitas Creeks; and along the Rio Grande (Monk, 1904). Information from eyewitnesses provided a basis for determining flood damage, which was estimated to be at least $1 million; of this amount, one-half was damage to railroads (Monk, 1904).

The flood of September 23, 1941, affected mostly the central part of the State. On September 23, 1941, the peak discharge of the Rio Puerco near Bernardo (fig. 3, site 3) was 18,800 ft3/s (cubic feet per second). Peak discharges of most streams in the affected areas had recurrence intervals greater than 50 years. Other areas that had peak discharges with recurrence intervals of less than 50 years probably also were affected by the flood; however, records do not exist to document streamflow conditions.

The September 1, 1942, flood affected the central and eastern parts of the State and, to a lesser extent, the northeastern part. Streamflow records indicate that peak discharges at most gaging stations had recurrence intervals of 50–75 years. On September 1, 1942, the peak discharge of the Pecos River near Puerto de Luna
(fig. 3, site 4) was 48,600 ft3/s, which has a recurrence interval greater than 100 years. Accounts by local residents indicate that the 1942 flood was of lesser magnitude than the 1904 flood.

The flood of June 17, 1965, likewise was not as severe as the flood of 1904. There was no loss of human life, but property damage was estimated to be tens of millions of dollars (Snipes and others, 1974). Streamflow records indicate that the 1965 flood had a recurrence interval greater than 100 years in many areas across the eastern part of the State. For example, on June 17, 1965, the peak discharge of the Vermejo River near Dawson (fig. 3, site 1) was 12,600 ft3/s, the peak discharge of record for that gaging station. This flood occurred during a major drought but did not have an appreciable effect on the drought because of the relatively short duration of the increased streamflows.

In addition to the floods previously described, severe flooding occurred in parts of the State on October 6, 1911 (water year 1912), June 29, 1927, April 24, 1942, December 19, 1978 (water year 1979), and June 9, 1988. In those instances, however, flooding was localized and did not cause widespread damage. The peak discharge of the October 6, 1911, flood has remained undetermined. However, the peak stage of the Animas River at Farmington (fig. 3, site 5) during the 1911 flood was about twice the stage of the flood of June 29, 1927, which had a peak discharge of about 25,000 ft3/s. The recurrence interval for the flood of June 29, 1927, on the Animas and San Juan Rivers exceeded 100 years, as did that of the flood of April 24, 1942, on the Rio Grande in the central part of the State. Major flooding on the Gila River near Redrock (fig. 3, site 6) on December 19, 1978, resulted in a peak discharge of 48,800 ft3/s. The flood of June 9, 1988, on the Vermejo River near Dawson (fig. 3, site 1) had a peak discharge of about 10,400 ft3/s. Floods of both the Gila River near Redrock on December 19, 1978, and the Vermejo River near Dawson on June 9, 1988, had recurrence intervals between 75 and 100 years.

DROUGHTS

Droughts are common in New Mexico. The normally meager annual precipitation causes extended periods of scant flow in the State’s unregulated rivers. Streamflow records can be used as one means to determine the duration and areal extent of droughts.

The duration, areal extent, and severity of major droughts in New Mexico are shown in figure 4. The areas of drought delineated on the maps are based on data from the six gaging stations shown in the figure and from other gaging stations statewide. However, only the gaging stations shown are used to describe the general severity of droughts.

The annual departure from average stream discharge for any year is the difference between the average discharge for that year, which is determined from daily streamflow records, and the average discharge for the period of record. Annual departures for the six selected gaging stations are shown in figure 4. A bar above the zero line is a positive departure from normal, and a bar below the zero line is a negative departure from normal. An extended period of negative departures indicates a hydrologic drought. Records for some gaging stations indicate an almost continuous deficiency of streamflow throughout a given drought, whereas records for other stations may indicate 1 or more years when streamflow was average or greater than average during a drought.

Such short-term reversals in trend can indicate two separate droughts or a short recovery period within the major drought. A study that employed a 5-year moving average to analyze streamflow within the Rio Grande basin showed that such reversals did not constitute recovery periods (Waltemeyer, 1987). Therefore, in this study, streamflow deficiencies were computed for each drought within the longer drought period to determine a recurrence interval.

Major long-term droughts occurred in New Mexico during 1931–41 and 1942–79. The duration of the two droughts differed among streamflow-gaging stations, and the dates represent the earliest beginning date and latest ending date common to most stations. For example, at five of the six gaging stations, the 1942–79 drought ended in 1979, but the start of the drought ranged from 1942 to 1948. Most gaging-station records from the statewide network indicate a sustained drought from 1950 to 1979.

The drought of 1931–41 affected the entire State. The Dust Bowl conditions in the Plains States probably are the most memorable aspect of this drought. Streamflow deficiencies in New Mexico during this period were significant but less severe than those during the subsequent drought. Streamflow records for the Vermejo River near Dawson (fig. 4, site 1), Rio Hondo near Valdez (fig. 4, site 3), and Pecos River near Pecos (fig. 4, site 4) indicate that the drought had recurrence intervals of 10–25 years in north-central New Mexico. In most of the State, however, the drought was severe and had a recurrence interval greater than 25 years. Nevertheless, no annual precipitation minimums were recorded at any weather station in the vicinity of the gaging stations during the 1931–41 drought.

An extended period of deficient streamflow affecting all of New Mexico lasted from the early 1940’s to late 1970’s (fig. 4). The 1942–79 drought greatly affected nonirrigated agricultural areas in New Mexico. Although farmers in the State have minimized the effect of drought on their crops by irrigating, dryland farming is still practiced for some crops, such as wheat. Wheat production in the 1950’s was the smallest since 1909 (Cockril, 1959). By the end of the 1950’s, about 2,000 wells had been drilled to supplement surface-water irrigation allotments, which had been decreased in response to the drought (Wayne Cunningham, Elephant Butte Irrigation District, oral commun., 1988). Precipitation records indicate the severity of the 1942–79 drought:  annual precipitation minimums were recorded at Albuquerque (4.06 inches in 1956), Farmington (4.07 inches in 1950), Carlsbad (4.40 inches in 1956), and Glenwood (6.90 inches in 1956) (Kunkel, 1984).

During the drought, streamflow deficiencies were recorded at all six gaging stations, and periods of greater than average annual departures generally did not exceed about 2 years. At Ute Creek near Logan (fig. 4, site 2), however, periods in which sustained streamflow deficiencies exceeded surpluses did not begin until 1961.

WATER MANAGEMENT

Federal, State, and local government agencies, acting on the authority of various statutes, are responsible for flood-plain management, flood-warning systems, and water-use management during drought. Historical records of streamflow provide much of the basis for New Mexico’s management of surface water during floods and droughts.

Flood-Plain Management.—The New Mexico State Engineer Office coordinates the National Flood Insurance Program, and the Federal Emergency Management Agency administers the program for participating counties. Insurance needs in special flood-hazard areas were met by the National Flood Insurance Act of 1968. The National Flood Disaster Protection Act of 1973 expanded the availability of insurance to other areas but imposed flood-plain management activities on property owners and communities. In addition, the Flood Control Act (P.L. 93–234) authorized the U.S. Army Corps of Engineers to provide flood-plain studies. These studies are similar to those conducted under the authority of the National Flood Insurance Program and are performed under the authority of the Federal Emergency Management Agency.

Flood-Warning Systems.—In conjunction with the U.S. Bureau of Reclamation, the U.S. Army Corps of Engineers operates multiple-purpose reservoirs throughout the State to provide water storage during floods. State statutes provide the State Engineer with authority to administer dam safety programs that provide for adequate design inflow and seismic stability. Flood-warning activities in the State are provided under the direction of the River Forecast Center of the National Weather Service. This flood-warning system issues current rainfall and streamflow data for strategic points statewide that can be used to alert reservoir managers in the event of a flood.

Water-Use Management During Droughts.—Most small streams in the State, excluding those in mountainous areas, are ephemeral. In contrast, the larger perennial streams have become water-transmission systems because of the construction of reservoirs. These reservoirs were designed and are operated, in part, to decrease streamflow variability and to ensure water supply for a multitude of purposes. State and Federal agencies determine who receives the water and in what quantities. The agencies acquire their authority from interstate compacts and State laws enacted through many years. The result is a system that minimizes the effect of droughts. For example, the agriculture industry, which is the largest user of surface and ground water in the State, minimizes the effect of drought on crop production through irrigation. In recent years the major controversy concerning water supply has been the overabundance of water within the water-distribution network (Hester, 1987).

SELECTED REFERENCES

Cockril, P.W., 1959, A statistical history of crop and livestock production in New Mexico: New Mexico State University, New Mexico Agricultural Experiment Station Bulletin 438, 35 p.

Hester, Nolan, 1987, Who are the outsiders?, in Harris, L.G., ed., Managing the river: Las Cruces, New Mexico, 31st Annual New Mexico Water Conference, Water Resources Research Institute, Proceedings, 264 p.

Kunkel, K.E., 1984, Temperature and precipitation summaries for selected New Mexico locations: New Mexico Department of Agriculture, Climate Report, 190 p.

Monk, G.B., 1904, Report of floods in New Mexico during September and October 1904: U.S. Geological Survey files, 25 p.

Snipes, R.J., and others, 1974, Floods of June 1965 in Arkansas River basin, Colorado, Kansas, and New Mexico: U.S. Geological Survey Water-Supply Paper 1850–D, 97 p.

U.S. Geological Survey, 1973, Hydrologic unit map of New Mexico: U.S. Geological Survey Hydrologic Unit Map, scale 1:500,000.

______1976–87, Water resources data for New Mexico, water years 1975–86: U.S. Geological Survey Water-Resources Data Reports NM–75–1 to NM–86–1, published annually.

______1986, National water summary 1985—Hydrologic events and surface-water resources: U.S. Geological Survey Water-Supply Paper 2300, 506 p.

______1990, National water summary 1987—Hydrologic events and water supply and use: U.S. Geological Survey Water-Supply Paper 2350, 553 p.

Waltemeyer, S.D., 1986, Techniques for estimating flood-flow frequency for unregulated streams in New Mexico: U.S. Geological Survey Water-Resources Investigations Report 86–4104, 56 p.

______1987, Trends in streamflow and reservoir contents in the Rio Grande basin, New Mexico: Las Cruces, 31st Annual New Mexico Water Conference, Water Resources Research Institute, Proceedings, 264 p.