Designing stormwater controls to protect streams from erosion—A simple (and implementable) channel-protection strategy

Stormwater control measures (SCM) must restrict erosive flows to reduce stream erosion in developed watersheds. Over 20 y ago, Bledsoe (2002) proposed the erosion potential approach, which suggests managing excess stormwater runoff to mimic the sediment transport capacity of the undeveloped flow regime. Subsequent research has documented that the benefits of this approach extend beyond stable streams and include improvements to biotic integrity and water quality. However, the lack of its widespread implementation, or that of any SCM approach that successfully limits stream erosion, underscores its challenges. In this paper we document the mechanics of integrating the erosion potential approach into stormwater management programs in northern Kentucky (NKY) and Austin, Texas, USA. We applied a simple strategy of capturing excess stormwater runoff and releasing it below the critical discharge for streambed erosion (Qc) for a single design storm. We calibrated the Qc design targets with local streambed mobility monitoring and sediment transport modeling, an important step in this relatively straightforward approach. The field-validated Qc threshold in NKY was ∼45% of the undeveloped 2-y peak discharge (Q2). The Qc threshold in Austin was 2% of Q2. Sediment transport modeling indicated that excess stream erosion can be mitigated by designing SCMs to restrict the 2-y design storm to be discharged at <Qc (0.45 × Q2) in NKY and to restrict the 2-mo design storm to be discharged at <Qc (0.02 × Q2) in Austin. In both cases, the cumulative sediment transport capacity for all standard design storms was less than the undeveloped flow regime. Designing stormwater features to incorporate a field-validated Qc threshold, in addition to meeting the local water-quality and flood-control design criteria, can achieve the intent of the erosion potential approach. Importantly, these 2 case studies illustrate that this approach does not appreciably increase SCM basin sizes or add burdensome design criteria on stormwater practitioners relative to standard flood-control and common water-quality criteria.