CIVE 633 - ENVIRONMENTAL HYDROLOGY

WETLAND HYDROLOGY AND WATER QUALITY

  • The flow and storage volume determine the length of time that water spends in the wetland and, thus, the opportunity for interactions between waterborne substances and the wetland ecosystem.

  • Wetlands lose water via streamflow, groundwater recharge and evapotranspiration.

  • Continuous source treatment wetlands would normally be isolated from groundwater.

  • Constructed treatment wetlands usually have uniform bottoms, and an absence of flow pattern effects.
DEFINITION OF HYDROLOGIC TERMS

  • Hydraulic loading rate q (HLR); cm/d, m/d, m/yr.

q = Q / A

  • Mean water depth h (d): m, cm.

  • Wetland water volume V; m3

  • Nominal detention time t; days.

t = V / Q

  • Superficial velocity v; m/d.

  • Hydroperiod: Used to designate all attributes of the water regime. Also, the number of days per year that there is surface water at a given wetland.
WATER BALANCE

  • Over any budget period, each flow rate adds or removes a corresponding volume of water:

    Vi - Vo + Vc - Vb - Vgw + Vsm + Vr - Ve = ΔVstored

    in which:

    • Vb= bank loss volume

    • Vc= catchment runoff volume

    • Ve= evaporated volume

    • Vgw = volume infiltrated to groundwater

    • Vi = input wastewater volume

    • Vo= output wastewater volume

    • Vr = rain volume

    • Vsm = snowmelt volume

    • ΔVstored = change in water storage in wetland.

WETLAND WATER QUALITY

  • Wetlands often cause improvements in quality for flow-through waters.

  • Wetlands do not produce perfectly pure water.

  • Nutrients are typically present at low levels in natural wetlands.

  • P is at low levels, often below 0.05 mg/L.

  • Organic nitrogen is formed in wetlands as a bioproduct of biomass decomposition.

  • N is low in natural wetlands, from 1 to 2 mg/L.

  • Nitrate and nitrite nitrogen are usually absent from natural wetland waters.

  • Denitrification is efficient in the natural wetland environment because the necessary carbon source is present together with the anoxic conditions that favor the utilization of nitrate as an electron acceptor.

  • Heavy metals are not present in natural wetland waters in high concentrations.

BIOGEOCHEMICAL CYCLING

  • The limnologist views the wetland as a shallow lake and emphasizes the water chemistry.

  • The soil scientist views the wetland as a waterlogged soil and emphasizes the wetland substrate.

  • The engineer views the wetland as a reactor vessel and emphasizes the degradation processes.

  • The botanist views the wetland as a water garden and emphasizes the plants and their taxonomy.

  • The hydrologist views the wetland as a vegetated channel.

  • The ecologist is concerned with types and communities of plants and animal species.

  • All points have merit, and there is danger in a narrow view.

  • Fig. 6-17 shows a simplified view of the wetland biogeochemical cycle.

 
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