Large infrequently operated river diversions for Mississippi delta restoration John W. Day a, b , Robert R. Lane a, b, * , Christopher F. D’Elia a , Adrian R.H. Wiegman a , Jeffrey S. Rutherford a , Gary P. Shaffer c , Christopher G. Brantley d , G. Paul Kemp a a Louisiana State University, Department of Oceanography & Coastal Sciences, College of the Coast & Environment, Louisiana State University, Baton Rouge, LA 70803, USA b Comite Resources, Inc.,11831 Port Hudson Pride Rd., Zachary, LA 70791, USA c Dept. of Biological Sciences, Southeastern Louisiana State University, Hammond, LA 70402, USA d U.S. Army Corps of Engineers, New Orleans District, Bonnet Carr e Spillway, PO Box 216, Norco, LA 70079, USA article info Article history: Received 1 March 2016 Received in revised form 25 April 2016 Accepted 3 May 2016 Available online xxx Keywords: Wetland Mississippi delta River diversions Climate change Energy scarcity abstract Currently the Mississippi delta stands as a highly degraded and threatened coastal ecosystem having lost about 25% of coastal wetlands during the 20th century. To address this problem, a $50 billion, 50-year restoration program is underway. A central component of this program is reintroduction of river wa- ter back into the deltaic plain to mimic natural functioning of the delta. However, opposition to di- versions has developed based on a number of perceived threats. These include over-freshening of coastal estuaries, displacement of fisheries, perceived water quality problems, and assertions that nutrients in river water leads to wetland deterioration. In addition, growing climate impacts and increasing scarcity and cost of energy will make coastal restoration more challenging and limit restoration options. We address these issues in the context of an analysis of natural and artificial diversions, crevasse splays, and small sub-delta lobes. We suggest that episodic large diversions and crevasses (>5000 m 3 s 1 ) can build land quickly while having transient impacts on the estuarine system. Small diversions (<200 m 3 s 1 ) that are more or less continuously operated build land slowly and can lead to over-freshening and water level stress. We use land building rates for different sized diversions and impacts of large periodic inputs of river water to coastal systems in the Mississippi delta to conclude that high discharge diversions oper- ated episodically will lead to rapid coastal restoration and alleviate concerns about diversions. Single diversion events have deposited sediments up to 40 cm in depth over areas up to 130e180 km 2 . This approach should have broad applicability to deltas globally. © 2016 Published by Elsevier Ltd. 1.0. Introduction: historical perspective Currently the Mississippi delta stands as a highly degraded and threatened coastal ecosystem. Before human activities impacted the delta, primarily in the 20th century, it was a healthy functioning ecosystem (Kolb and van Lopik, 1958; Condrey et al., 2014; Muth, 2014). In this paper we discuss how the delta was formed and sustained, the causes of deterioration, and the potential use of very large but episodic diversions for wetland creation while minimizing negative impacts that arise when diversions are operated continuously. Since the stabilization of sea level approximately 5000 years ago and prior to massive human impact, mainly in the 20th century, the Mississippi River formed a vast deltaic wetland complex encom- passing about 25,000 km 2 in the north central Gulf of Mexico (Roberts, 1997; Day et al., 2007, 2014). One need only look at the northern Gulf coast to recognize that riverine inputs formed the delta, which protrudes out into the Gulf more than a degree of latitude compared to coastlines east and west of the delta. The coastlines on either side of the delta tend to be coastal bays fronted by linear barrier islands. It is a truism that it was the river that built the delta, but this question bears looking into in more detail. Condrey et al. (2014) used maps and journals of early European explorers to describe what they called the last natural delta of the Mississippi that existed just prior to European settlement. The delta * Corresponding author. Louisiana State University, Department of Oceanography & Coastal Sciences, College of the Coast & Environment, Louisiana State University, Baton Rouge, LA 70803, USA. Contents lists available at ScienceDirect Estuarine, Coastal and Shelf Science journal homepage: www.elsevier.com/locate/ecss http://dx.doi.org/10.1016/j.ecss.2016.05.001 0272-7714/© 2016 Published by Elsevier Ltd. Estuarine, Coastal and Shelf Science xxx (2016) 1e12 Please cite this article in press as: Day, J.W., et al., Large infrequently operated river diversions for Mississippi delta restoration, Estuarine, Coastal and Shelf Science (2016), http://dx.doi.org/10.1016/j.ecss.2016.05.001