Landscape Urbanism Studio | UW Dept of Landscape Architecture | Winter 2005
performance analysis

Evaluation showed design interventions to be moderately to highly successful at meeting detention requirements while using non-traditional stormwater strategies (shown as % of detention requirement met):

By surface type:

 

 

 

By landuse type:

Roofs (13):

Parking lots (7):

R.O.W. (7)

 

Public Spaces (3):

Commercial/Retail (5):

Mixed Use/Residential (3):

Industrial/Warehouse (5):

R.O.W. (7):

80 – 500+%

70 – 300+%

90 – 600+%

 

80 – 200+%

90 – 1000+%

80 – 500+%

70 – 600+%

90 – 500+%

(numbers in parentheses show the number of students whose design addressed a category)

 

 

Design performance for detention/retention of stormwater was evaluated using methods outlined in Seattle's Flow Control Manual including:

i. design hyetograph determination

ii. modeling of stormflow/detention needed for target site

Further work included:

iii. calculating water quality treatment (when provided in a design)

iv. experimental measurement of other parameters

 

 

I. Design Hyetograph

Design Storm - 24-hr duration with recurrence intervals:

Private Parcels : 25-yr storm

R.O.W. : 2-yr storm

Two unit-hyetographs were provided:

1). the Flow Control Manual storm

2). a storm obtained from analysis of precipitation data from Seattle sub-basins (Precip Analysis Report).

<< Comparison showed the Flow Control Manual storm to be more intense

- all comparison percentages are derived from the Flow Control Manual hyetograph -

 

 

II. Stormwater Model

To determine impact at the site-scale, Flow Control Manual numbers for allowable site discharge were used to calculate the detention needed to lighten impact on the entire system, yielding:

Private Parcels : 0.2 cfs/acre

R.O.W. : 0.15 cfs/acre

<<This information was incorporated into a user-friendly Excel model

 

 

 

 

IV. Physical Experiments

Since information (such as void space of locally-available landscape materials) were not available, a team of students measured some of these parameters to improve performance calculations in the stormwater model.

 

<< results in Excel

 

 

 

students in action >>