Part II LID Hydraulic Impact Analysis Jerry P. Preston, P.E., CFM EHRA, Inc. jpreston@ehrainc.com
South of FM 529 and north of W. Little York Road Blvd is the west boundary Langham Creek is the east boundary Rice University February 26, 2013
Goal of modern conventional drainage is to remove runoff quickly, efficiently and completely Conventional drainage achieves this goal, but requires large infrastructure expense LID DRAINAGE REQUIRES A CHANGE OF PERSPECTIVE EHRA, Inc.
LID DRAINAGE REQUIRES A CHANGE OF PERSPECTIVE LID drainage concepts and principals: decentralize conveyance and detention treat runoff at its source distributed micro-scale practices - spread it out mimic natural drainage processes time of concentration, infiltration, volume and flow time-tested technology, different application like conventional methods, drainage is still designed to avoid flood damages and support mobility slower does not mean less efficient
HCFCD CHANNEL Raingardens Underground storage Pervious pavement (parking) NORTH Vegetated swales
HYDROLOGY Analyzed 2-year (6-hour), 10-year (24- hour) and 100-year (24-hour) events Rational Method Peak Flow for each DA Hydrographs for each DA using Clark s UH Method in HEC-HMS Used actual Tc and calibrated Storage Coefficient R to match Rational Method Peak Flow
HYDROLOGY 7.2-ac site divided into 41 inlet drainage areas: Pervious pavement sections Vegetated swales Raingardens
HYDRAULICS Dynamic routing using EPA-SWMM software System of nodes and links Nodes: Raingardens (storage area) Pervious Pavement (storage area) Manholes/Junctions Links: Underground pipe (6-24 ) Overflow Inlets
HYDRAULICS 3 outfalls into adjacent HCFCD channel 54 nodes 51 links
RAIN GARDEN = DETENTION STORAGE
RAIN TANKS aka DETENTION STORAGE
VOID VOLUME = DETENTION STORAGE
ENGINEERED SOIL FILTER FOR SWQ
ENGINEERED SOIL FILTER with UNDERDRAIN and OVERFLOW INLET
2-year System Hydrographs
10-year System Hydrographs
100-year System Hydrographs
EVALUATING RESULTS Pre- Development Post- Development Peak 100-yr Runoff Rate 11.7 cfs 7.9 cfs Peak 10-yr Runoff Rate 8.5 cfs 6.9 cfs Peak 2-yr Runoff Rate 6.0 cfs 5.9 cfs Time of Concentration 16.7 min. 18.1 min. Total detention storage provided (sum of storage utilized in permeable paver subgrade, raingardens and vegetated swales) = 2.7 ac-ft Total detention storage rate = 0.38 ac-ft/ac (Typical detention storage rate = 0.55 ac-ft/ac)
CONCLUSION Distributed micro-scale features contribute to more efficient detention storage, no adverse impact to receiving stream Engineered soil filter provides dramatically better SWQ benefits compared to conventional trash rack Much greater engineering/analysis effort required than conventional route Net result: more efficient land plan + attractive product = happy client!
Thank You Questions? Edminster Hinshaw Russ & Associates, Inc. Civil Engineering Surveying Land Planning Platting Landscape Architecture Hydrology & Hydraulics Construction Phase Services Public Works Bridges & Structures Transportation Planning Rice University February 26, 2013