Assessing environmental flows (e-flows) for urban rivers is important for water resources planning and river protection. Many e-flow assessment methods have been established based on species’ habitat provision requirements and pollutant dilution requirements. To avoid flood risk, however, many urban rivers have been transformed into straight, trapezoidal-profiled concrete channels, leading to the disappearance of valuable species. With the construction of water pollution-control projects, pollutant inputs into rivers have been effectively controlled in some urban rivers. For these rivers, the e-flows determined by traditional methods will be very small, and will consequently lead to a low priority being given to river protection in future water resources allocation and management. To more effectively assess the e-flows of channelized urban rivers, we propose three e-flow degrees, according to longitudinal hydrological connectivity (high, medium, and low), in addition to the pollutant dilution water requirement determined by the mass-balance equation. In the high connectivity scenario, the intent is for the e-flows to maintain flow velocity, which can ensure the self-purification of rivers and reduce algal blooms; in the medium connectivity scenario, the intent is for the e-flows to permanently maintain the longitudinal hydrological connectivity of rivers that are isolated into several ponds by means of weirs, in order to ensure the exchange of material, energy, and information in rivers; and in the low connectivity scenario, the intent is for the e-flows to intermittently connect isolated ponds every few days (which is designed to further reduce e-flows). The proposed methods have been used in Shiwuli River, China, to demonstrate their effectiveness. The new methods can offer more precise and realistic e-flow results and can effectively direct the construction and management of e-flow supply projects.