Technical Abstract: Experiments were conducted using a soil-mantled flume subjected to simulated rain and downstream baselevel lowering to quantify the growth, development, and evolution of rills and rill networks. Digital elevation models constructed using photogrammetric techniques greatly facilitated data acquisition and analysis. Results show that: (1) headcuts formed by baselevel lowering were the primary drivers of rill incision and network development, and the communication of this wave of degradation occurred very quickly and efficiently through the landscape, (2) rill networks extended upstream by headcut erosion, where channels bifurcated and filled the available space, (3) rill incision, channel development, and peaks in sediment efflux occurred episodically, linked directly to the downstream baselevel adjustments, and (4) sediment discharge and rill drainage density approached nearly constant or asymptotic values with time following baselevel adjustments despite the continuous application of rainfall. These findings have important implications for the prediction of soil loss, rill network development, and landscape evolution where headcut erosion can occur.