The Abundance, Size, and Spacing of Lakes and Reservoirs Connected to River Networks

Descriptions of river network topology do not include lakes/reservoirs that are connected to rivers. We describe the properties and scaling patterns of river network topology across the contiguous United States: how lake/reservoir abundance, median lake/reservoir size, and median lake/reservoir spacing change with river size. Typically, lake/reservoir abundance decreases, median lake/reservoir size increases, but median lake/reservoir spacing is uniform across river size. There is a characteristic lake/reservoir size of 0.01–0.05 km2 and a characteristic lake/reservoir spacing of 1–5 km that shifts to 27–61 km in larger rivers. Climate explains more of the variance in river network topology than both glacial history and constructed reservoirs. Our results provide conceptual models for building river network topologies to assess how lake/reservoir abundance, size, and spacing effect the transport, storage, and cycling of water, materials, and organisms across networks. Plain Language Summary Rivers and lakes/reservoirs serve different hydrologic, ecologic, and economic roles and are often studied as separate systems. Yet there are many lakes/reservoirs connected to rivers and this connectivity has profound impacts on sediment storage and transport, biogeochemical cycles, and aquatic habitat in both rivers and lakes/reservoirs. Defining the topology of river networks is critical for understanding these processes across entire networks of connected rivers and lakes/reservoirs. We defined river network topology by scaling the abundance, size, and spacing of lakes/reservoirs with river size and identified broadscale controls of network topology. Key Points Lakes/reservoirs connected to rivers decrease in abundance, increase in size, but are uniform in spacing as river size increases River network topology with lakes/reservoirs can be classified into four types across the contiguous United States Climate is a major control of river network topology with lakes/reservoirs