ArkNavReport_TOC_Acronyms_ExecSummary.doc

Common characteristics of these two components

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Common characteristics of these two components include: New disposal sites to accommodate continuing channel maintenance dredging (primarily in Oklahoma), and Construction of additional river training structures to facilitate the maintenance of the navigation channel (primarily in Arkansas). Flow Management Feature: On the MKARNS navigation traffic is severely restricted when flows reach 100,000 cubic feet per second (cfs) and tow owners generally reduce tow sizes when flows are above 60,000cfs. The proposed River Flow Management Action is to improve the safety and efficiency of commercial navigation operations by managing the MKARNS to limit periods of sustained high flows. This could be achieved by reducing the number of days when river flows exceed 100,000 cfs and the number of days exceeding 60,000cfs at Van Buren. In addition, other authorized project purposes, including flood control, recreation; hydropower; water supply; and fish and wildlife would be maintained. The existing operation plan of the MKARNS has been in place since 1986. Key characteristics of the existing plan are: 150,000 cfs releases. When flood storage in the controlling reservoirs is above 10 percent in the spring or 18 percent the remainder of the year, releases from the reservoirs are set at approximately 150,000 cfs which corresponds to the 22-foot stage at Van Buren, AR. A 75,000 cfs bench. When the 11 controlling reservoirs’ flood storage falls to within the range of 3 – 10 percent in the spring or 9 - 10 percent the rest of the year, the flow is held constant at 75,000 cfs at Van Buren, AR. The purpose of the bench is to accomplish water releases from flood storage while lowering the rate of release to below 80,000 cfs for the benefit of navigation and low-lying farms along the river. A taper operation of 40,000 cfs to 20,000 cfs. When the flood storage remaining in the 11 controlling reservoirs fall to below 3 percent in the spring, below 11 percent in the summer, or below 9 percent the remainder of the year; the target flow at Van Buren, AR is gradually reduced from 40,000 cfs to 20,000 cfs. Dredging operations can occur on the river to remove sediment deposited during high flows when flows fall below 40,000 cfs. Twenty three possible components of the flow management feature were evaluated. These components were developed with input from local, xiii
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State and Federal agencies, as well as the public. These 23 components were compared using the USACE SUPER (Southwestern Division Modeling System for the Simulation of the Regulation of a Multipurpose Reservoir System) Model. The SUPER Model program was run for each of the initial components. Key information derived by the model to screen each component included: River flow and duration, The 11 controlling reservoirs stage and duration, and Operational damages within the system (including to public and private lands) Of the 23 river flow components, four operational components were evaluated in detail. With the exception of the No Action Component, the bench was changed from 75,000 cfs to 60,000 cfs.
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