Amarillo is located in an area known as the High Plains of Texas, which is located in the southern part of the Great Plains. Flat prairies characterize this area with slopes in the range of 0.2%. Elevations of the City are in the general range of 3500 ft. Mean Sea Level (MSL). Naturally, runoff generally follows a poorly defined pattern, flowing into the playas from the surrounding nearly level areas. There are areas in town located among the Canadian River Breaks, which naturally have a well-developed drainage system, however, a large portion of the City lies upon the plains. A unique characteristic of this area is the playas. These are dish-shaped depressions ranging in size from a few square yards to several square miles in size. Most of the playas within the City are considered medium to large playas. These are sometimes called wet weather lakes because of the method by which the lakes receive water. Playas are unique because the typical playa loses the majority of its water to infiltration and evaporation. These lakes normally are not interconnected to one another by creeks or streams and have no definite outlet. Extremely heavy rains for a very extended period of time would be required in order for one playa to breech its drainage basin and drain into another basin within the City. Due to the flat slopes of the plains and the general infeasibility of draining from one playa to another, the design of storm water systems can be extremely challenging. Feasible design alternatives quickly become limited. Flat slopes make it difficult to provide detention or retention facilities economically. In effect, each playa is a retention facility in itself.
The City encompasses approximately 58,000 acres of land area at this time. Not all of the incorporated area is served by storm water conveyances, and there is a significant portion of the City that is used as agricultural land. Current estimates are that the MS4 serves approximately 40 percent of the area within the City limits, or about 23,000 acres.
Most of the regulated storm water runoff drains to playa lakes located throughout the City. The surface areas of the playas range from a few acres to over 100 acres. There are 18 major playas that function as part of the City’s MS4 at this time. Under normal conditions, the playas have no discharge, and therefore provide terminal storage for their respective drainage basins. Accumulated runoff is managed by evaporation to the atmosphere or infiltration to the subsurface.
Urbanization around most playas is at a sufficient distance from the playas to minimize the chance of flooding of buildings or infrastructure from accumulated water.
Within the more urbanized portions of the City, however, the City has constructed pumping and piping systems to move water from one playa to another, and eventually to man-made impoundments located within the Canadian River watershed in the northern portion of the City. These lakes then discharge into natural drainage-ways that drain eventually into the Canadian River. One outfall is Thompson Park, designated as Outfall 001, and the second outfall is Medi-Park, designated as Outfall 002. Both of these facilities have a series of reservoirs on the upstream side of the outfall acting as retention facilities.
Amarillo averages approximately 19.5 inches of rain per year. Rains typically occur as intense thundershowers, usually accompanied by intense electrical storms. Annual snowfall averages approximately 17 inches. Individual snowfall events range in depth from trace amounts to rare events of slightly more than 20 inches. Temperature ranges from approximately 105° F down to –10° F throughout the year.