Effects of distributed and centralized stormwater best management practices and land cover on urban stream hydrology at the catchment scale

This is a paired watershed research study to compare stormwater management strategy effects, including riparian buffer and tree canopy cover, on urban hydrology.

Key Findings:

• Predominant catchment treatments included

o Centralized (gray infrastructure) BMPs

With little tree canopy cover (~15% UTC)

With greater tree canopy cover (~57% UTC)

o Distributed (GSI) BMPs (~21% UTC)

o Non-urbanized, forested landscape (~85% tree canopy cover)

• Results

o Compared with centralized treatments, GSI provided

 Slightly less stormwater runoff (6.5%)

 Significantly greater base flow (36%) and total water runoff (20%)

o GSI BMPs provided better hydrologic control for storms <27mm

o Centralized BMPs enabled better hydrologic control for storms >27mm

o Watersheds with greater tree cover (57% and 85%) had about 33% lower runoff volumes for stormflow, baseflow, and total flow

• Conclusions

o GSI BMPs compared with centralized BMPs

 Had increased baseflow

 Reduced maximum volume discharge (during smaller rain events)

 Reduced stream response (during smaller rain events)

 More closely resembles hydrologic response of forested catchment

o Increased tree canopy cover

 Reduced total stormwater runoff volume

 Decreased stream response during rain events

o Important considerations for urban stream hydrology

 Land cover is an effective stormwater BMP

• Reduced impervious cover

• Increased tree canopy cover

 Implement distributed (GSI) BMPs with land cover consideration

o Implications of GSI BMPs (engineered and natural)

 Less intense discharge

 Reduced erosion and particulate transport

 Improved stream hydrology

 Increased nutrient retention and removal