Name: _____________________
Date: _____________________
Module 3.6: Intermediate LID Design: Hydrologic Modeling
General instructions: You may model facility dimensions to the nearest half foot.
Site:
WSU Extension in Everett
2000 Tower St. Everett, WA 98201
Site Design Assumptions:
Predominant Soil:
Till
Pre-developed Land Cover:
Forest
Site:
Post-developed Land Cover:
Impervious
Design Standard:
Water Quality Treatment (91% Infiltration)
Project:
New construction of 5,000 square foot moderately sloped parking lot. Design a
bioretention system to provide water quality treatment for all 5,000 sf of
parking area.
Facility Design Assumptions:
Sideslopes:
3:1
Ponding Depth:
6 inches
Freeboard:
6 inches
BSM Thickness:
18 inches
BSM Porosity:
40 % effective porosity (“porosity” – “wilting”)
(46 % porosity in WWHM)
BSM Infiltration Rate:
6 inches/hour
Native Soil Infiltration Rate:
0.5 inches/hour
Overflow pipe diameter:
12 inches
Assume:
No underdrain permitted
Square facility geometry
Neglect facility footprint in post-developed area
15 minute computational timestep
Results:
WWHM
Facility Bottom Area:
___________ square feet
Facility Footprint:
___________ square feet
Percent of Development:
___________ % (top area)
MGSFlood
Facility Bottom Area:
___________ square feet
Facility Footprint:
___________ square feet
Percent of Development:
___________ % (top area
Exercise #2: Modeling Bioretention and Permeable Pavement
Exercise #2a: Bioretention (Water Quality)
Module 3.6: Intermediate LID Design: Hydrologic Modeling
Site:
Post-developed Land Cover:
Impervious
Design Standard:
Flow Control (match predeveloped flows and
durations from 50% 2-year to full 50-year
recurrence interval flow)
Project:
New construction of 5,000 square foot moderately sloped parking lot. Design a
bioretention system to provide flow control for all 5,000 sf of parking area. Use
same facility assumptions as Exercise 1a.
Use a 15 minute computational timestep.
Results:
MGSFlood
Facility Bottom Area:
___________ square feet
Facility Footprint:
___________ square feet
Percent of Development:
___________ %
Exercise #2b: Bioretention (Flow Control)
Module 3.6: Intermediate LID Design: Hydrologic Modeling
Site:
Post-developed Land Cover:
Impervious/Permeable Pavement
Design Standard:
Flow Control (match predeveloped flows and
durations from 50% 2-year to full 50-year
recurrence interval flow)
Project:
New construction of 5,000 square foot parking lot. Design permeable pavement
facility to provide flow control for 2,000 square feet of permeable pavement
(parking stalls) and run-on from 3,000 square feet of adjacent impervious
parking area (driving lanes).
Facility Design Assumptions:
Pervious Area:
2,000 square feet
Pavement Slope:
2 % (model as flat, layout check dams outside
of model to provide required ponding)
Pavement Infiltration Rate:
50 inches/hour
Gravel Porosity:
30%
Native Soil Infiltration Rate:
0.5 inches/hour
Use a 15 minute computational timestep.
Results:
WWHM
Average Ponding Depth:
___________ feet
MGSFlood
Average Ponding Depth:
___________ feet
Exercise #2c: Permeable Pavement