Linking Water Treatment with Wetland Restoration - Restorative Redevelopment of Devastated Ecocultural Landscapes - page 368

Some design suggestions can be offered about how to distribute flow in created
or restored wetlands (Bays 2004). It is critically important to do everything possible
to promote an even sheet flow by making maximal use and efficiency of the area
available in order to maximize remedial treatment by bacteria and plants through
minimizing the potential for short circuiting. It is also important to maintain low
flow velocities to minimize erosion and sediment resuspension. Sheet flow can be
maintained through the use of multiple outlets which have the effect of reducing
corner dead zones by ensuring a uniform pattern in movement or by installing a deep
zone collector system at the end of the wetland.
Water movement in wetlands is not uniform due to the fact that with increasing
depth in a system, drag increases in proximity to the sediments and bottom veg-
etation. In larger open-water wetlands such as those in Iraq, wind-induced mix-
ing occurs which differentially circulates water through the wetlands depending
on bottom topography. Because deeper areas get preferential flow, this turns into
a major design issue since there is need to ensure adequate flow to all regions of
the wetland. Work is currently underway on developing a hydrodynamic model
(Lightbody, S., pers. comm.) that will be a major step forward in how to approach
managing surface-flow wetlands by generating models to predict water move-
ment patterns through these systems under different design scenarios. For exam-
ple, one approach to improving hydraulic efficiency in wetlands is to create deep
zones that are akin, for example, to the kind of pathways seen in pictures (France
2007) of how the marsh Arabs used their boats to travel around the islands and
along the canals within the system. These different deep zones, if oriented per-
pendicular to flow, turn into opportunities for re-areated water to slow down and
respread out through the system as well as providing habitat areas for fish and
other wildlife and also opportunities for solid settling and removal in the system
(Bays 2004).
Such wetland design components are typically brought into a wetland to respond
to these hydraulic issues, as, for example, at the Tres Rios wetlands in Arizona,
a water treatment project built by CH2MHILL in an arid region receiving scant
rainfall. The demonstration project, which has provided great insight into how to
operate wetlands in this arid region, is characterized by alternating deep and shallow
zones as well as habitat islands and outlet control structures. Hydraulic analysis has
shown that adding deep zones served to increase the hydraulic efficiency and led to
improvements in water quality performance (Bays 2004).
In terms of distributing water to wetlands, solutions can be simple up-flow stand
pipes, initial spreader swales, or the more costly grated pipes. Shallow marsh zones are
required for the best water quality treatment (France 2003). Water collection follow-
ing transport through wetlands can be simple open pools, ponds, or collector swales.
PLANTING DESIGN
Plants can be installed or allowed to colonize naturally. In the United States, it is
extremely rare to adopt a completely natural colonization approach because many
plants that would become established may actually be somewhat deleterious to the
cover and development of other more desirable plant communities (Bays 2004).