Monitoring sediment yield is necessary for assessing erosion induced land degradation and used for planning conservation measures. Collecting time and space integrated as well as time distributed runoff samples cost-effectively is still a challenge for hydrologists, civil engineers, soil scientists, and environmentalists. A low-cost automatic runoff sampler for quantifying suspended sediment using simple mechanical and hydraulic principles was designed, and a prototype developed. The procedure of runoff sampling involves the interception of a defined portion of the runoff exiting the crest of a gauging structure through the triangular sectioned interceptors. The intercepted volume was reduced to a manageable quantity by multiple splitting using a series of diamond sectioned interceptors. After the collection of a representative volume, the sample was delivered to a time-stamped storage system through a clock-driven arm tube. The mathematical design principles at each stage defined the hydraulic and mechanical dimensions of the components which were assembled to develop the complete prototype. Furthermore, field-scale modifications to accommodate any special situations and conditions were also presented. The prototype of the sampling device endured rigorous laboratory-scale validation tests and was found to perform reasonably well. The performance of the new sampling device was evaluated against the fine resolution manual discrete sampling. The temporal resolution of 15 min adopted by the sampler was found reasonably comparable to further finer resolution options with discrepancies contained within a ± 10% error envelope (R2 = 0.983). The equipment was validated in field-scale experiments both in plot and natural watershed and performance metrics were found to be acceptable (R2 = 0.78 to 0.99). Moreover, low cost and easy maintenance requirements indicate the high potential and field applicability of this new device.