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This chapter discusses the endangered rivers of the United States, and the actions required to save them. It reveals that rivers of the Lower Mississippi region were first heavily impacted by dramatically increased sediment yields from lands being cleared of natural vegetation for growing crops. River response to sedimentation prompted humans to undertake widespread channelization, construction of levees, clearing of logjams and naturally occurring wood, and destruction of riverside and floodplain habitats. Rivers of the Central region have been most altered by flow regulation and changes in sediment supply associated with dams, diversions, and channelization, and by contamination from agricultural runoff. The chapter discusses how the big rivers of the Southwestern Canyon region were most heavily affected by the construction of numerous large dams and the removal of water for off-stream agricultural and municipal uses during the twentieth century.

This chapter describes the challenges posed by the Missouri River as Lewis and Clark made their way west. Topics covered include the river's meandering, the treachery of the river, the social consequences of the variability and fickleness of the Missouri, efforts to tame rivers using machine-age technology, and the impact of the straightening and channelization of the Missouri on natural ecological systems of the river valley.

There is a place, about a mile long by a thousand feet wide, that lies in the heart of the Southern Rocky Mountains in Colorado. Here at the eastern margin of Rocky Mountain National Park, along a creek known as North St. Vrain, everything comes together to create a bead strung along the thread of the creek. The bead is a wider portion of the valley, a place where the rushing waters diffuse into a maze of channels and seep into the sediment flooring the valley. In summer the willows and river birch growing across the valley bottom glow a brighter hue of green among the darker conifers. In winter, subtle shades of orange and gold suffuse the bare willow stems protruding above the drifted snow. The bead holds a complex spatial mosaic composed of active stream channels; abandoned channels; newly built beaver dams bristling with gnawed-end pieces of wood; long-abandoned dams now covered with willows and grasses but still forming linear berms; ponds gradually filling with sediment in which sedges and rushes grow thickly; and narrow canals and holes hidden by tall grass: all of these reflect the activities of generations of beavers. This is a beaver meadow. The bead of the beaver meadow is partly hidden, tucked into a fold in this landscape of conifers and mountains. The approach is from Route 7, which runs north–south across the undulating topography of creeks flowing east toward the plains. Coming from the north, as I commonly do, you turn west into the North St. Vrain watershed on an unpaved road perched on a dry terrace above the creek. The road appears to be on the valley bottom, but beyond the terrace the valley floor drops another 20 feet or so to the level at which the creek flows. I instinctively pause at this drop-off. The conifer forest on the terrace is open and the walking is easy. The beaver meadow looks impenetrable and nearly is. I have to stoop, wade, crawl, wind, and bend my way through it, insinuating my body among the densely growing willow stems and thigh-high grasses.

June, when the snows come hurrying from the hills and the bridges often go, in the words of Emily Dickinson. In the beaver meadow, the snows are indeed hurrying from the surrounding hills. Every one of the 32 square miles of terrain upslope from the beaver meadow received many inches of snow over the course of the winter. Some of the snow sublimated back into the atmosphere. Some melted and infiltrated into the soil and fractured bedrock, recharging the groundwater that moves slowly downslope and into the meadow. A lot of the snow sat on the slopes, compacted by the weight of overlying snow into a dense, water-rich mass that now melts rapidly and hurries down to the valley bottoms. North St. Vrain Creek overflows into the beaver meadow, the water spilling over the banks and into the willow thickets in a rush. I can hear the roar of water in the main channel well before I can see it through the partially emerged leaves of the willows. Overhead is the cloudless sky of a summer morning. A bit of snow lingers at the top of the moraines. Grass nearly to my knees hides the treacherous footing of this quivering world that is terra non-firma. I am surrounded by the new growth of early summer, yet the rich scents of decay rise every time I sink into the muck. I walk with care, staggering occasionally, in this patchy, complex world that the beavers have created. I abruptly sink to mid-thigh in a muck-bottomed hole, releasing the scent of rotten eggs, but less than a yard away a small pocket of upland plants is establishing a roothold in a drier patch. A seedling spruce rises above ground junipers shedding yellow pollen dust and the meticulously sorted, tiny pebbles of a harvester ant mound. I extract my leg with difficulty and continue walking. As I walk around the margin of another small pond, the water shakes. Sometimes the bottom is firm in these little ponds, sometimes it’s mucky–I can’t tell simply by looking through the water.

The first week of September mostly feels like summer. The air on the dry terrace bordering the beaver meadow is richly scented with pine. Purple aster, blue harebells, and tall, yellow black-eyed Susan still bloom. Fungi are more abundant on the forest floor, and the tiny, purplish berries of kinnikinnick are sweet to the taste. The air is warm in the sunshine, but strong winds hurry rain showers through at intervals. Patches of last year’s snow linger on the surrounding peaks, even as the first light snows have already fallen in the high country. Down in the beaver meadow, the leaves of aspen, willow, birch, and alder are starting to assume their autumn colors. Here and there a small patch of yellow or orange appears among the green. Blades of grass have a pale orange tint and the strawberry leaves have gone scarlet, even as white asters, purple thistles, and a few other flowers continue to bloom. The creek is noticeably lower, its cobble bed slick with rust-brown algae. Exposed cobble and sandbars have grown wider as the water has shrunk back from the edge of the willows, and the main channel is easy to cross on foot. The clear water is chillingly cold in both the main channel and the side channels. The smaller side channels no longer flow, and a drape of mud mixed with bits of plants covers the cobbles. Wood deposited a year ago has weathered to pale gray. The older, marginal beaver ponds have shrunk noticeably, and the water is lower in the main ponds, where tall sedges now lie bent on the top of the declining water surface. The beavers remain active: following fresh moose tracks, I come on a newly built beaver dam on a small side channel. By the third week of September, autumn has clearly arrived in the mountains. The air remains quite warm during the day, but nights of frost are swiftly bringing out the autumn colors. Whole stands of willows and aspen now glow golden or pumpkin-orange.

The hydrologic, sedimentologic, and geomorphic processes of the Northern Rio Grande as outlined in the previous chapters do not operate under natural, undisturbed conditions. Numerous engineering structures and activities have modified the processes and forms, and so an explanation of the movement and storage of contaminants in the system requires knowledge of the channelization and dam construction in the region. Channelization works are usually directed toward controlling the horizontal position of the channel, keeping it aligned in an economically advantageous arrangement, and maintaining a clear path for floodwaters to prevent them from spilling over the banks. The imposition of an artificial, stable channel on a naturally unstable system is rarely completely successful, but even with partial success, the newly defined system is a radical departure from the natural one. Floodwaters usually flow through modified channels at higher velocities than they do through natural channels, and so they may transmit more sediment in the channel. Low flows, however, may deposit sediment in the engineered channel, thereby reducing its efficiency and raising its bed. The abandonment of previously active minor channels or braided sections provides new areas of colonization for riparian vegetation, which may enhance sedimentation when flows exceed the capacity of the designed channel. The construction of dams obviously disrupts river processes in the reservoir area but has indirect effects throughout the river system because of newly instituted controls on flood flows, normal low flows, and sediment discharges. The first engineering structures on the Rio Grande probably appeared about A.D. 1200. With the collapse of irrigation societies in the Salt and Gila River valleys in Arizona and in tributaries of the San Juan River in Colorado and New Mexico, migrants moved into the Rio Grande Valley. By the time of the Spanish incursions in the middle and late sixteenth century, the native population had developed extensive irrigation systems along the entire Northern Rio Grande to support numerous pueblos.4 Diversion works on the main stream probably consisted of brush and boulder structures that directed the water into canal entrances through the low banks. These structures probably washed away with each spring flood.