Changes

==Post-to-predevelopment water balance matching==

==Post-to-predevelopment water balance matching==

The amount of infiltration required on a given site is determined by comparing water balance estimates before and after development. Ideally, the volume of water infiltrated and evapotranspired prior to development would remain the same afterwards.  

The amount of infiltration required on a given site is determined by comparing water balance estimates before and after development. Ideally, the volume of water infiltrated and evapotranspired prior to development would remain the same afterwards.  

In practice, increased impervious cover normally results in lower post development evapotranspiration. Best efforts should be made to match pre-development water balance components.  However, in some cases maintaining runoff volumes at predevelopment levels may require that more water is infiltrated after development than under the predevelopment condition.   

In practice, increased impervious cover normally results in lower post development [[evapotranspiration]]. Best efforts should be made to match pre-development water balance components.  However, in some cases maintaining runoff volumes at predevelopment levels may require that more water is infiltrated after development than under the predevelopment condition.   

Under natural conditions, sites with fine textured native soils will have lower infiltration volumes (and higher runoff) than those with coarse textured soils. On fine textured soils with very low permeability (hydrologic D type soils), the measured infiltration rate may even approach zero. Under these conditions, the stormwater management approach should focus on runoff prevention and volume reduction through evapotranspiration or water reuse, rather than infiltration.

Under natural conditions, sites with fine textured native soils will have lower infiltration volumes (and higher runoff) than those with coarse textured soils. On fine textured soils with very low permeability (hydrologic D type soils), the measured infiltration rate may even approach zero. Under these conditions, the stormwater management approach should focus on runoff prevention and volume reduction through evapotranspiration or water reuse, rather than infiltration.