Hydrology and Hydrodynamics

Human Activities Affect Watershed Hydrology

Regional changes in climate have led to a trend of increasing precipitation in PIE watersheds.  At the same time suburbanization has increased the acreage of impervious surfaces and resulting runoff, as well as the channelization of flow into streams for storm water management.  However these trends are masked by the effects of other water management practices  that  divert water away from the watershed.  These activities include pumping of groundwater, cross basin transfers, and most dramatically, water withdrawals for municipal water supplies. 

There have also been local water shortages in summer, thought to be driven by lawn irrigation.  These “suburban droughts” have led to policy changes regulating water use at the town and state level.  Interestingly, our social science research reveals that intensive yard care practices, such as irrigation and fertilizer application, occur less often in the PIE watersheds than expected.  Our surveys and interviews with homeowners suggest that (1) PIE lawn cover patterns may not be as strongly linked to lifestyle patterns as in other areas, (2) an innovative residential water pricing scheme has been effective in reducing the importance of lawn cover on local water use.  Even though policy and recent price changes have reduced residential water-use, in the coming decades water-use may exceed mandated limits.  More info… Williams et al. 2004; Williams et al. 2005; Claessens et al. 2006) (Pellerin et al. 2008; Claessens et al. 2006; Schneider and Pontius 2001; Polsky et al., 2012; Schneider and Pontius 2001; Polskyet al., 2012; Polsky et al. 2009; Hill and Polsky 2005, 2007; Guha 2009

 

Wave erosion of marsh enhanced by sea level rise

Salt marshes and tidal flats co-evolve over long time frames, with oneretreating or expanding at the expense of the other.  The trajectory of this evolution results from complex interactions among physical and biological processes, including tidal currents, wind waves, sediment erosion or deposition, and vegetation.  This balance may be shifted as a function of sea level rise.   Geomorphologists at PIE are exploring the effects of tidal currents and wave sheer stress on the erosion of marsh edges and how the importance of these forces differs depending on the size of the tidal flats, which in turn may depend on relative sea level.  Models show that at lower sea level states, tidal basins are shallower, increasing dissipation of wave energy and therefore erosion.  At higher sea level, tidal basins are deeper, leading to higher waves and increased erosion at marsh boundaries.   When sea level rise becomes too high, marshes drown and are transformed into tidal flats.   Future 3D modeling at PIE will  quantify the exchange of sediments between Plum Island Sound and the marshes.  More info...See Mariotti and Fagherazzi (2010), Fagherazzi et al 2006; Fagherazzi et al 2007.