Oligohaline tidal channels (sloughs) in the Pacific Northwest were shown to have allometric form with respect to outlet width and depth, channel length, perimeter, and surface area. In contrast, an artificial slough, excavated to mitigate port improvements, did not conform to natural slough allometry, resulting in high retention of allochthonous inputs and sediment accumulation. Additionally, intertidal sedge habitat abundance was related to slough size for smaller sloughs, but larger sloughs did not fit this allometric pattern. This suggests that sedge habitat in large sloughs has been destroyed due to extensive log storage and transportation from the 1890s to the 1970s. Finally, the abundance of salmonid prey of terrestrial origin—aphids and adult flies—in slough surface waters was correlated with slough perimeter and, for aphids, with the amount of intertidal sedge habitat. An allometric perspective on landscape form and function has several implications for habitat restoration and mitigation: (1) Size-related constraints on replication for landscape-scale studies are loosened (e.g., rather than requiring reference sites that are similar in size to experimental sites, analysis of covariance can be used to control size effects); (2) physical processes, such as sedimentation and erosion, affect landscape form, whereas landscape form can affect ecological processes, so design of restoration or mitigation projects should conform to allometric patterns to maximize physical and ecological predictability; (3) landscape allometry may provide insight into undocumented human disturbances; and (4) allometric patterns suggest design goals and criteria for success.