Figure 1 shows the Norman WFO’s area of river forecasting responsibility. This large area includes more than 50 river forecast locations and consists of the western two-thirds of Oklahoma and a portion of northcentral Texas. The Norman WFO is responsible for four major river systems from where they enter western Oklahoma and end in eastern Oklahoma in flood storage pools of three large reservoirs. Starting in the northwest corner, these rivers are the Cimarron and Salt Fork of the Arkansas Rivers, which drain into Keystone Lake. Next is the Canadian River that feeds Eufaula Lake. Finally, the Red River runs along the WFO’s southern border and enters Lake Texoma. Together these rivers provide drainage for more than 135,000 square miles of Oklahoma, northeast New Mexico, southeast Colorado, southwest Kansas, and the Texas Panhandle.

Upper reaches of the drainage basins in New Mexico and Panhandles of Texas and Oklahoma have soils with high infiltration rates, and therefore are non-contributing to the floods in central Oklahoma. The fall of the rivers gradually decreases from about 6 feet per mile in western Oklahoma to less than 2 feet per mile as they enter eastern Oklahoma. Channels are broad, meandering and sand-filled with the active water courses only occupying a small portion of the flood plain. Low water channels are continually shifting with variations in stream flow.

Compared to eastern Oklahoma, the flood control capacity of central Oklahoma is limited. Other than a few large dams in far western Oklahoma, most of the flood retaining structures in the Norman WFO area are small dams with drainage areas of one to ten square miles. More than two thousand of these

As shown in Figure 2, average annual rainfall amounts across the Norman WFO increase from about 20 inches in the west to more than 35 inches in the east. In late spring or early fall, storms can often produce locally heavy rains which create a high potential for uncontrolled flooding in most of central and western Oklahoma.

The Enid Storm of 1973 produced 15-20 inches of rainfall over a 100-square-mile area, with 12 inches falling in three hours. Flooding may become widespread when storms repeatedly develop over the same terrain or move slowly eastward along the drainage courses of the major rivers. This type event occurred in October 1986 when the remnants of Hurricane Paine dropped from 10 inches of rain in southwestern Oklahoma to almost 20 inches in north-central Oklahoma to southern Kansas with nearly a 10-inch basin average for the area above Keystone Lake.

Norman WFO Service Hydrologist, Steven Kruckenberg, identified non-supported river gage stations as the major forecasting challenge for his area. These are gages that may only have a wire-weight and require an observer to make a reading or an automated gage where flows are not measured. Without measurements, stage-discharge ratingsare difficult to determine accurately. At wire weight stations, the data is usually only collected during a significant flood event and even then may be sporadic. Additionally, some of the stations are located in regions where flood events are infrequent, making the limited data even more important. Models used at the ABRFC for river forecasting are impossible to calibrate accurately without this important data. Fortunately, the USGS has developed a plan to provide reliable stream flow data for all river forecast locations, but so far the funding only allows for a few stations to be added to their system every year. Two stations are to be upgraded by this plan in FY 2002. They are Cimarron River near Buffalo, which is a forecast point, and Skeleton Creek near Lovell which will aid forecasting the Cimarron River at Perkins.

In early 2000, hydrologists from both the ABRFC and West Gulf RFC (WGRFC) in Fort Worth, Texas joined forces and created a categorical river forecast verification system. This new system, created after countless hours of development and testing, promises to provide useful statistics to RFCs about how well they are forecasting rivers when forecasts are needed the most, during flooding.