Chapter 16: Running Water

Water collected in drainage basins or watersheds flows toward outlets, with drainage patterns revealing underlying geology: dendritic networks form on uniform materials, radial patterns radiate from domes and volcanic cones, rectangular patterns follow jointed rock systems, and trellis patterns develop in folded mountain terrain. Rivers function through three distinct zones where sediment is produced in steep headwater regions, transported along main channels, and deposited near river mouths. Stream velocity depends on multiple factors including channel gradient, cross-sectional shape, surface roughness, and discharge volume, and paradoxically increases downstream despite declining gradient due to larger channels and reduced friction. Streams erode landscapes through mechanical quarrying of bedrock, abrasion of channel surfaces, and chemical dissolution of soluble rock types. Sediment movement occurs in three forms: dissolved materials invisible in water, suspended sediment that clouds the water column, and bed load particles rolling and bouncing along the bottom. Stream capacity refers to total sediment load potential while competence indicates the largest particle size a stream can transport, both increasing dramatically during flood events. Channel morphology varies between bedrock channels with steep gradients and rapids, and alluvial channels that develop characteristic meandering patterns with cut banks and point bars, or braided patterns when sediment supply fluctuates. Valley development progresses from narrow V-shaped canyons with waterfalls to broad floodplains shaped by lateral migration of meanders. Changes in base level fundamentally alter erosional processes: lowering base level causes vertical incision and creates terrace features, while raising it reduces stream power and promotes sediment deposition. Major depositional features include deltas with distinctive foreset and bottomset bed structures, natural levees along channel margins, and alluvial fans at mountain fronts. The chapter concludes by addressing flood hazards and management strategies, distinguishing between regional floods from sustained precipitation or snowmelt, flash floods from intense storms, ice-jam floods on frozen rivers, and catastrophic dam-failure floods, with control approaches ranging from structural solutions like levees and dams to nonstructural management emphasizing appropriate land use zoning and floodplain preservation.