Development and Demonstration of a GIS-Based Cumulative Effectiveness Approach to Buffer Design and Evaluation

A methodology for incorporating site-specific landscape characteristics into vegetated stream buffer design has been developed. This methodology consists of calculations within a geographic information system format, and applies a sequential accumulation of the contribution of individual pixels of buffer width to overall performance. A demonstration of the application of the methodology to a watershed expecting development is presented here and implications for decision making are discussed. Information layers derived from landscape data layers and used in buffer-performance calculations are displayed. Specific calculations performed in the demonstration are buffer delineation, with implications related to the potential impact of variable versus fixed width buffers, to the impact of assumptions with respect to the type of sediment needing to be settled out, and to the need to mandate wider buffer widths adjacent to lower order streams. Sediment-trapping efficiency calculations can be used to set performance standards and assess the viability of certain criteria in terms of areas potentially available for buffers. The reduction in peak discharges of storm-water runoff ( through some combination of infiltration and detention) is becoming a surrogate water-quality parameter for non-point-source pollution in recent total maximum daily load determinations. Infiltration-volume estimation can be used in assessing the feasibility of such a surrogate approach. (C) 2014 American Society of Civil Engineers.