"土砂流量" can be translated as "sediment flow rate" or "soil and sand flow rate" in English, depending on the specific context and the level of technicality required.
"Sediment flow rate" is a more technical and precise term, often used in engineering, geology, or environmental science contexts when referring to the quantity of sediment (which can include soil, sand, and other particulate matter) moving through a particular area or channel over a certain period of time.
"Soil and sand flow rate" is a more straightforward and descriptive translation, which might be preferred in less technical or more general contexts where clarity is key.