Harris, John AllenMany rivers along the Atlantic Coast contain major knickpoints, which define the Fall Zone. These often-urbanized rivers straddle multiple physiographic regions with spatial variations in lithology, topography, and hydrology. This research evaluates the effects of mainstem channel incision and urbanization on channel and catchment morphology, bed substrate mobility, catchment water storage dynamics, and hydrologic response in tributaries of the Northwest Branch of the Anacostia River above and below the Fall Zone knickpoint. Topographic analyses show that differential incision below the mainstem knickpoint has initiated steep secondary channels incised into bedrock. Measurements at representative reaches show that bankfull shear stress exceeds critical shear stress in these newly initiated tributaries, resulting in erosive channels outside of threshold conditions. Increased urban runoff introduced at storm drain outfalls maintains these non-steady state conditions. Geophysical surveys reveal that regolith depth for water storage capacity is primarily below the flatter ridgetops of the tributary catchments, where development is concentrated. The secondary tributaries cannot access these upland storage zones, and thus have limited infiltration and recharge capacity. I installed streamgages in the tributaries and constructed catchment water balances to study storage dynamics and hydrologic response. Hydrologic consequences of urbanizing the steep secondary tributaries include flashy, elevated stormflows, greater total runoff, and reduced baseflows that are not maintained during drought periods. The combination of steep channels, thin regolith, and urban overprint limits infiltration to moderate storm responses and recharge storage. These effects were not seen in non-urbanized secondary tributaries, urbanized tributaries above the knickpoint, or the forested reference streams above the Fall Zone. These findings define the geomorphic adjustment of tributaries to differential mainstem incision and explore the hydrologic impacts of urbanizing small steep catchments with limited effective storage capacity. Supplementary files:S1: Table with the location, drainage area, stream gradient, bankfull hydraulic values, and grain size values at each Northwest Branch tributary and reference reach used in the study. S2: Spreadsheet with the water level logger gage height values collected at 5-minute intervals from April 2023-March 2024 and calculated discharge from the Northwest Branch tributary streamgages. S3: Spreadsheet with the monthly water balance values for the Northwest Branch tributary catchments and reference watersheds from April 2023-March 2024. S4: Table with the depth to bedrock values and corresponding slope angles measured from the seismic profiles and LiDAR-derived digital elevation models.enThesisHydrologic sciencesGeomorphology