Arkansas River Channel Capacity and Riparian Habitat Planning Study

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ARKANSAS RIVER FROM OTERO/PUEBLO COUNTY LINE i 7 6 1J TO JOHN MARTIN DAM CHANNEL CAPACITY AND RIPARIAN HABITAT PLANNING STUDY Prepared for the ' Colorado Water Conservation Board by the U.S, Army Corps of Engineers, Albuquerque District under the authority of the Planning Assistance to States Program August 2001 SUMMARY OF FINDINGS AND RECOMMENDATIONS The channel capacity of the Arkansas River above John Martin Dam has decreased significantly over time. In the early 1900's the channel capacity for Problem Areas 1, 2 and 3 i was 15,000 cubic feet per second (cfs). By 1965, channel capacity had decreased to about 10,000 cfs and since the 1999 flood flows the channel capacity is now between 1,000 and 3,000 cfs due to encroachment on the floodway by development and vegetation and sediment. Other ' studies also showed a problem with high water table resulting in subsurface damage to crops in many areas of the flood plain. In October, 1999, the Colorado Water Conservation Board (CWCB) requested planning assistance from the U.S. Army Corps of Engineers, Albuquerque District (Corps) for restoring hydraulic capacity and riverine /riparian ecosystem values in the Arkansas River above John Martin Dam. A Planning Assistance to States (Section 22) agreement (50150 cost share) was signed by the CWCB and Corps in December 10, 1999. This study's purpose is to develop and evaluate plans which, when implemented, can improve channel capacity for flood flows and restore riverine and riparian habitat along the Arkansas River above John Martin Dam. Changes in current reservoir operation plans were not a study objective. The Arkansas River study reach extends between the Otero/Pueblo county line and John Martin Reservoir. The CWCB and Corps coordinated with local and state interests to identify three specific problem areas to investigate, totaling approximately 11 river - miles. The three I areas selected for study do not include all known problems within the reach upstream of John Martin Reservoir, nor are they necessarily the most crucial, Rather, they were selected as examples of typical problems within the reach. A geomorphological assessment, which included the study reach was completed in 1997 by the U.S. Army Corps of Engineers Waterways Experiment Station and provided an overview of the geologic, climatologic, and hydrologic forces influencing the Arkansas River during the past century. The Albuquerque District conducted all hydraulic and ecological investigations. 0 ff I