Restoring ecological integrity of great rivers: historical hydrographs aid in defining reference conditions for the Missouri River

Abstract

Restoring the ecological integrity of regulated large rivers necessitates characterizing the natural flow regime. We applied 'Indicators of Hydrologic Alteration' to assess the natural range of variation of the Missouri River's flow regime at 11 locations before (1929-1948) and after (1967-1996) mainstem impoundment. The 3768 km long Missouri River was divided into three sections: upper basin least-altered from flow regulation, including the lower Yellowstone River; middle basin inter-reservoir, and lower basin channelized. Flow regulation was associated with a reduction in magnitude and duration of the annual flood pulse, an increase in magnitude and duration of annual discharge minima, a reduction in frequency of annual low-flow pulses, earlier timing of March-October low-flow pulses, and a general increase in frequency of flow reversals with a reduction in the rate of change in river flows. Hydrologic alterations were smallest at two least-altered upper-basin sites and most frequent and severe in interreservoir and upper-channelized river sections. The influence of reservoir operations on depressing the annual flood pulse was partially offset by tributary inflow in the lower 600 km of river. Reservoir operations could be modified to more closely approximate the 1929-1948 flow regime to establish a simulated natural riverine ecosystem. For inter-reservoir and upper channelized-river sections, we recommend periodic controlled flooding through managed reservoir releases during June and July; increased magnitude, frequency and duration of annual high-flow pulses; and increased annual rates of hydrograph rises and falls. All of the regulated Missouri River would benefit from reduced reservoir discharges during August-February, modified timing of reservoir releases and a reduced number of annual hydrograph reversals. Assessment of ecological responses to a reregulation of Missouri River flows that more closely approximates the natural flow regime should then be used in an adaptive fashion to further adjust reservoir operations.

Growth rate responses of Missouri and Lower Yellowstone River fishes to a latitudinal gradient

“…Hesse & Mestl (1993), Pegg (2000) and Galat & Lipkin (2000) reported that the hydrologic regime along the upper channelized portion of the Missouri River has been drastically altered from the pre-impoundment condition. Some of these changes include higher flow rates, reduced flow variability and loss of slack water habitats for refugia suggesting a more extreme environment than was historically present.…”

Hydrological alteration along the Missouri River Basin: A time series approach

“…In this regard, we present an alternative method in an attempt to validate previous work assessing hydrological alteration along the Missouri River. Hydrological alterations made on the Missouri River have been qualitatively and/or regionally evaluated in several studies (Slizeski et al, 1982;Hesse and Mestl, 1993), but few published studies have attempted a more quantitative approach to assessing the extent of these alterations (e.g., Galat and Lipkin, 2000). Here, we present a different approach (time series modeling) than that of Galat and Lipkin (2000) to quantitatively test for differences in flow patterns associated with large-scale structural changes throughout the mainstem Missouri River.…”

“…Hydrological alterations made on the Missouri River have been qualitatively and/or regionally evaluated in several studies (Slizeski et al, 1982;Hesse and Mestl, 1993), but few published studies have attempted a more quantitative approach to assessing the extent of these alterations (e.g., Galat and Lipkin, 2000). Here, we present a different approach (time series modeling) than that of Galat and Lipkin (2000) to quantitatively test for differences in flow patterns associated with large-scale structural changes throughout the mainstem Missouri River. Our specific objectives were to (1) develop time series models of daily mean flow for 10 Missouri River locations with data series encompassing pre-and post-alteration periods, (2) test for significant differences in daily mean flow between pre-and post-alteration periods using data from the entire year, and (3) test for differences in daily mean flow between pre-and post-alteration periods using data restricted to the spring fish spawning season (1 April -30 June).…”

“…Poff et al (1997) identified magnitude of discharge, frequency of flow extremes, duration of a given flow condition, timing of extremes, and the rate of change from one flow to another as major components of flow that regulate ecological processes. All or part of these five components have been used to evaluate various aspects of how flow has changed before and after large-scale management in lotic systems (Richter et al, 1996;Galat and Lipkin, 2000). Most of these studies used summary statistics and indices that define general hydrological conditions from daily flows to characterize the degree of hydrological alteration at several gauges within a system.…”

“…Most of these studies used summary statistics and indices that define general hydrological conditions from daily flows to characterize the degree of hydrological alteration at several gauges within a system. For example, using the Index of Hydrological Alteration (IHA), Galat and Lipkin (2000) reported that Missouri River flows were most affected in reaches that were heavily influenced by reservoirs.…”