Arkansas River Channel Capacity and Riparian Habitat Planning Study

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IJ ARKANSAS RIVER FROM OTERO/PUEBLO COUNTY LINE TO JOHN MARTIN RESERVOIR CHANNEL CAPACITY AND RIPARIAN HABITAT PLANNING STUDY 1. INTRODUCTION The channel capacity of the Arkansas River in Problem Areas 1, 2 and 3 above John Martin Dam, has decreased significantly over time. When Pueblo Darn was completed in 1975, the channel capacity was estimated to be 15,000 cubic feet per second (cfs). By 1965, channel capacity had decreased to about 10,000 cfs due to encroachment on the floodway by development and vegetation (USACE 1983). During the spring of 1999, reported flood flows revealed that the channel was not able to convey flows of even 3,000 cfs, due to decreased ' channel capacities and caused backwater effects, including a high water table and subsurface damage to crops in many areas of the flood plain. 1 In an October 1, 1999, Ietter to the U.S. Army Corps of Engineers, AIbuquerque District (Corps), the Colorado Water Conservation Board (CWCB) formally requested Section 22 planning assistance for restoring hydraulic capacity and riverine /riparian ecosystem values in the Arkansas River above John Martin Dam. A Planning Assistance to the States (Section 22) agreement (50150 cost share) was signed on December 10, 1999. ' 1.1 STUDY AUTHORITY This channel capacity and riparian habitat planning study was performed under authority of the U.S. Army Corps of Engineers, Albuquerque District, Planning Assistance to States Program. The program's authority stems from Section 22. of the Water Resources Development Act of 1974 (Public Law 93 -251), as amended. Section 22 authorizes the Secretary of the Army, acting through the Chief of Engineers, to assist the states in the preparation of comprehensive plans for the development, utilization and conservation of water and related land resources of drainage basins, watersheds, or ecosystems. Section 22 studies are undertaken for planning, not M design and construction, purposes. 1.2 STUDY PURPOSE The study's purpose is to develop and evaluate long -term maintenance plans which, when implemented, can improve channel capacity for flood flows and restore riverine and riparian habitat along the Arkansas River above John Martin Darn. Investigation of changes to the current reservoir operation plan was not a study objective. ' 1.3 STUDY REACH AND TYPICAL PROBLEM AREAS This study will focus on three specific problem areas within the reach of the Arkansas River between the Otero/Pueblo county line and John Martin Reservoir. Two primary problems have been identified within these three problem areas: high groundwater table and reduced channel capacity. This study involved a cooperative effort between the CWCB and the Corps to analyze