John Martin Reservoir is a reservoir on the Arkansas River in Bent County in southeastern Colorado. Built and managed by the U.S. Army Corps of Engineers, it is used for flood control, irrigation, and recreation. John Martin Reservoir State Park lies on its shore.
History
In the 1930s, U.S. Representative from Colorado John Martin successfully advocated for legislation in the U.S. Congress approving the building of a reservoir on the Arkansas River for the purposes of flood control. Signed into law in 1939 by President Roosevelt, the legislation assigned the task of construction to the U.S. Army Corps of Engineers. The effort required the U.S. government to buy more than of land, including most of the town of Caddoa, and relocate of Santa Fe Railway track.
Construction of Caddoa Dam and Reservoir started in the fall of 1939. Rep. Martin died that year, and, in June 1940, both the dam and reservoir were renamed in his honor. Storage of water in the reservoir began in January 1943. The diversion of resources to fighting World War II caused delays in the project until 1946. The dam was finally completed in October 1948.
In 1935 the U.S. Army Corps established the Tucumcari District to develop the Conchas Project in Eastern New Mexico. At the conclusion of the construction of the Conchas Project the focus of the District moved to Caddoa, Colorado to construct the Caddoa Reservoir Project. The District staff relocated to Caddoa Colorado on December 4, 1939. At this time the District name was changed to the Caddoa District. In 1942 with the advent of World War Two the District made its final move to Albuquerque, New Mexico and was renamed the Albuquerque District which has remained the same since. At this time the focus of the district switched from Civil Works to Wartime activities which included work to facilitate the development of Los Alamos Laboratory and their development of atomic energy and its application to weapons.
In December 1948, the state governments of Colorado and Kansas signed the Arkansas River Compact, an agreement governing the two states' access to the river's water, including John Martin Reservoir. In 1980, the states developed a plan allocating 60% of the reservoir's water to Colorado and 40% to Kansas. Adherence to the Compact has been a recurrent source of controversy between the two states, serving as a primary factor in the decades-long water conflict litigation Kansas v. Colorado.
Geography
John Martin Reservoir is located at (38.0730328, -103.0279951) at an elevation of . It lies in southeastern Colorado in the Colorado Piedmont region of the Great Plains. The entirety of the reservoir lies within Bent County.
The reservoir is impounded at its eastern end by John Martin Dam. The dam is located at (38.0666741, -102.9371452) at an elevation of . The Arkansas River is both the reservoir's primary inflow from the west and outflow to the east. Smaller tributaries include Rule Creek, which flows into the reservoir from the south, and Gageby Creek, which flows in from the north.
U.S. Route 50 runs generally east-west north of the reservoir. Colorado State Highway 183 runs north-south between U.S. 50 and Fort Lyon immediately northwest of the reservoir. A BNSF Railway line runs generally east-west along the reservoir's southern shoreline, crossing the southern arm fed by Rule Creek.
The city of Las Animas lies on the south bank of the Arkansas River west of the reservoir. Hasty, an unincorporated community, is located on U.S. 50 roughly north of the reservoir's eastern end. Caddoa, also unincorporated, lies immediately east of the dam.
Climate
According to the Köppen Climate Classification system, John Martin Dam has a cold semi-arid climate, abbreviated "BSk" on climate maps. The hottest temperature recorded at John Martin Dam was on July 20, 2019, while the coldest temperature recorded was on January 30, 1949, January 18–19, 1984 and February 15, 2021. The reading is the highest reliably measured temperature ever recorded in the state of Colorado.
Hydrography
The surface area, surface elevation, and water volume of the reservoir fluctuate based on inflow and local climatic conditions. In terms of capacity, the Corps of Engineers vertically divides the reservoir into a set of pools based on volume and water level, and the reservoir is considered full when filled to the capacity of its recreation and conservation pool. When full, John Martin Reservoir has a surface area of , a surface elevation of , and a volume of . When filled to maximum capacity, it has a surface area of , a surface elevation of , and a volume of .