CIVE 633 - ENVIRONMENTAL HYDROLOGY
WETLAND HYDROLOGY AND WATER QUALITY
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- 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
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- Hydraulic loading rate q (HLR); cm/d, m/d, m/yr.
- Mean water depth h (d): m, cm.
- Wetland water volume V; m3
- Nominal detention time t; days.
- 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.
- Over any budget period, each flow rate adds or removes a corresponding volume of water:
Vi - Vo + Vc - Vb - Vgw + Vsm + Vr - Ve = ΔVstored
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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.
- 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.
- 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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