U.S. Department of Defense
Date of this Version
2011
Abstract
Spring pulse releases for the benefit of the endangered pallid sturgeon were planned for March and May 2009 to mimic historic natural spring rises that occurred on the Missouri River before the closure of the main stem dams. The March spring pulse from Gavins Point Dam was not released in 2009 due to high downstream flows and the possibility of flow-limit violations. A 6.1 -kcfs May spring pulse was released in 2009.
The May spring pulse was monitored at 44 sites along the Missouri River. Nineteen of these were interior-drainage sites that were monitored for possible socioeconomic impacts to landowners. Socioeconomic impacts include gate closures, pumping, and overbank flooding. To help identify socioeconomic impacts, berm and field elevations were surveyed near the installed gages in March 2009 to better characterize possible overbank flooding. The location of the created spring pulse in the record was determined through the use of travel times from Gavins Point Dam.
The 2009 May spring pulse created no socioeconomic impacts at any of the monitored sites.
A flow attenuation rate was estimated for the May 2009 spring pulse using observed flow records at eight main stem gages along the Missouri River. The 6.1-kcfs spring pulse was estimated to attenuate at a rate of 1.1 kcfs for every 100 river miles in May 2009. The observed May 2009 spring pulse was 1.5 kcfs at Kansas City, MO and is estimated to have attenuated by 77%. Similar results were determined for the 4.5-kcfs March 2008 spring pulse in the 2008 monitoring report. The March 2008 spring pulse attenuated at a rate of 1.1 kcfs for every 100 river miles and was not distinguishable by Kansas City, MO.
A stage attenuation rate was also estimated for the May 2009 spring pulse. In general, the 1.8-ft May 2009 spring pulse attenuated at an approximate rate of 0.4 ft for every 100 river miles. This analysis was also completed for the March 2008 and May 2006 spring pulses. The 1.5-ft March 2008 spring pulse attenuated at a rate of 0.4 ft for every 100 river miles, and the 2.7-ft May 2006 spring pulse attenuated at a rate of 0.3 ft for every 100 river miles.
Flow reductions were made from dams tributary to the Missouri River to eliminate the created spring rise below Kansas City, MO. This reduction lowered the stage of the created spring rise. A stage change due to the created spring rise is still visible below Kansas City, MO, but the created spring rise is effectively reduced in elevation.
The effects of additional natural-spring rises were monitored at each site to help quantify flows that would result in landowner impacts. Where socioeconomic impacts (i.e. gate closures, pumping, and overbank flooding) did occur due to these flows, the duration of the impacts and impact-flow thresholds were estimated. Impact-flow thresholds are flows in the Missouri River at the river mile of the impacted site when the stage over the sensor of the gage becomes high enough to cause gate closures, pumping, or overbank flooding at a site.
The durations of high flows in the Missouri River in 2009 were much shorter than they were in 2008. The 2008 record experienced a long duration large rise that began in late May and continued through mid-June or early July depending on the river location. In contrast, the 2009 record experienced several shorter duration rises scattered throughout the record.
Table 1 summarizes the results for the 2006, 2008, and 2009 monitoring periods. Natural spring rise results are not shown for 2006 because only the spring pulse was monitored that year. Figure E1 shows the sites impacted by natural spring rises in 2009 and 2008 plotted by their RM locations along the Missouri River and the estimated flows in the Missouri River at the sites that resulted in gage closures.
Comments
Published by the U.S. Army Corps of Engineers (2011) 1-281