Transcript The Bay Area Hydrology Model: A Tool for Analyzing Hydromodification

The Bay Area Hydrology Model: A
Tool for Analyzing Hydromodification
Effects of Development Projects
and Sizing Solutions
Jill C. Bicknell, P.E., EOA , Inc.
Santa Clara Valley Urban Runoff Program
Doug Beyerlein, P.E., Clear Creek Solutions, Inc.
The Bay Area Hydrology Model: A
Tool for Analyzing Hydromodification
Effects of Development Projects
and Sizing Solutions
This presentation given by Jill Bicknell and Doug Beyerlein at
the September 2006 CASQA Conference in Sacramento, CA.
Acknowledgements
 Funding Agencies
– Santa Clara Valley Urban Runoff Pollution
Prevention Program (SCVURPPP)
– Alameda Countywide Clean Water
Program (ACCWP)
– San Mateo Countywide Stormwater
Pollution Prevention Program (STOPPP)
 Arleen Feng (ACCWP)
 Tony Donigian (Aqua Terra Consultants)
 Gary Palhegyi (GeoSyntec Consultants)
Presentation Overview
 Background / Permit Requirements
 Technical Approach to Control of
Hydromodification
 Design Challenges / Need for BAHM
 Overview of the BAHM
 BAHM Parameter Development
 BAHM Application
BAHM = Bay Area Hydrology Model
What is Hydromodification?
 Change in the runoff hydrograph (flow
pattern) from an area due to development
 Impacts of land development:
–
–
–
–
Increase in impervious surface
Decrease in amount of vegetation
Grading and compaction of soils
Construction of drainage facilities
What is Hydromodification?
(continued)
 Effects of land development on the site
runoff hydrograph:
– Less infiltration / evapotranspiration
– More surface runoff (increased volume)
– Runoff leaves the site faster (increased
peak flows)
– Runoff occurs more often (increased
duration)
– Runoff conveyed directly to creek (increased
connectivity)
Hydromodification Control
Requirements
SF Bay Area Phase 1 MS4 Permits
Permit Provision C.3.f.i.:
 Increases in runoff peak flow, volume,
and duration shall be managed for all
Group 1 Projects*, where such increased
flow and/or volume can cause increased
erosion of creek beds and banks…
* Group 1 = > 1 acre impervious surface
Hydromodification Control
Requirements
Permit Provision C.3.f.i. (continued):
 Post-project runoff shall not exceed
estimated pre-project rates and/or
durations, where the increased storm
water discharge rates and durations will
result in increased potential for erosion…
 Must develop and implement HydroModification Management Plans (HMPs)
Hydromodification Control
Requirements
Permit Provision C.3.f.ii. (Exemptions):
 Projects that discharge to tidal area, channel
continuously hardened to the Bay, or directly to
the Bay
 Projects that are “infill projects” in “highly
developed watersheds”
 Other projects where potential for increased
erosion is minimal (e.g., no increase in
impervious area)
Segment 5
Stable stream, bed close to old tree
Segment 4
Channel incision
on Yerba Buena
Creek
Segment 1
Undermining outfall protection structure
Pre- and postproject runoff
characteristics
All Events Flood Frequency
1000
Peak Q, cfs
900
800
Future Peak Q
Existing Peak Q
700
600
500
Pre-Urban Peak Q
400
300
200
100
0
Flow Duration
1
10
10000
1000
Return Period, months
Critical flow (Qc=15 cfs)
Durations (hrs)
100
1000
2-year
100
Pre-Urban
Existing
Frequency of
events and duration
10
1
10
80
150
220
290
360
Flows (cfs)
430
500
570
640
Control Strategies
 Peak flow control - not effective for erosion
control (low flows matter)
 Single event/design storm approaches –
not adequate hydromod control
 Flow duration control - recommended
– Maintain magnitude and duration of postproject flows same as pre-project
– Considers multi-year discharge record
 Site design (LID) measures – effective in
reducing flow, use to supplement flow
duration control facility
Flow Duration Histograms
Histogram of Discharge from the 716 Acre Test Subcatchment
10000
10-year
Peak Flow
5-year
Peak Flow
2-year
Peak Flow
Pre-Project Discharge
Post-Project Discharge
Frequency (hours)
1000
Post-Project w/Control
100
10
1
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
Flow Bin (cfs)
80
85
90
95 100 105 110 115 120 125 130 135
Flow Duration Curve Matching
San Jose Small 12-lot Residential Example
3
Pre-Project
Post-Project
2.5
Post-Project w/BMP
Discharge (cfs)
2
1.5
1
0.5
0
1
10
100
Frequency (hours)
1000
10000
Range of Storms to Manage
(Set of Design Storms)
 Qc to the 10-year event
Percentage of Total Work Done
100%
90%
80%
70%
60%
50%
40%
30%
20%
2-Year Peak
Flow
10%
5-Year Peak
Flow
10-Year Peak
Flow
0%
0
500
1000
Flow (cfs)
1500
2000
Tale of Five HMPs
 Santa Clara Valley
– Submitted Final HMP Report April 2005
– RWQCB adopted July 2005
 Contra Costa County
– Submitted Final HMP May 2005
– RWQCB adopted July 2006
 San Mateo & Alameda Counties, Fairfield-Suisun
– Submitted final HMPs, under review by RWQCB
– Adopt December 2006?
Performance Criteria
 Applicable projects with on-site flow
controls that are designed to provide flow
duration control to the pre-project condition
are considered to comply with the HMP.
 Flow duration controls shall be designed to
match pre- and post-project flow rates and
durations from 10% of the pre-project 2year peak flow to the pre-project 10-year
peak flow.
On-Site Options
 Use site design techniques to
reduce runoff flow and volume
– Decrease impervious surface area
– Disconnect impervious areas
– Promote infiltration
 Select treatment BMPs
that reduce volume
– swales, detention areas,
bioretention, green roofs
On-Site Options, continued
 Construct flow control structures
– Retention/detention basins
– Underground vaults/tanks
 Combine flow control with flood
control and/or treatment facilities
– Examples: detention basin, wet pond,
constructed wetlands
Overflow provision for peak
events (storage may also be
increased to meet flood
control requirements)
C
Inflows: site runoff after
reductions from site design,
infiltration or other retention
measures
A
D
E - released at
maximum discharge
rate in pipe
Dead storage
(optional)
Discharge to
stream
*
Point of Compliance: drainage
point for comparing post-project
and pre-project Flow Duration
curves
B
Bottom infiltration
where applicable
Legend: A) outlet pipe riser; B) low flow orifice;
C) intermediate orifice (1 shown); D) weir notch
(V-type shown); E) freeboard above riser
(typically 1 foot).
Schematic Flow Duration Control Pond
Integrating Flow Duration Control
(FDC) with Other BMPs
Urban
Runoff
FDC Basin
Bio-infiltration
Swale
FDC
Basin
Stream
FDC
Vault
Bio-infiltration
Swale
On-Site BMPs
LID
Process for Evaluating
Flow Control Requirements
Hydrologic Analysis
 Generate pre- vs. post-project flow
duration curves using hydrologic model
 Continuous simulation required
 Available models:
– Corps of Engineers’ HEC-HMS
– EPA HSPF
– EPA SWMM
– Western Washington Hydrology Model
Design Challenges
 Challenge #1: Flow duration control design
– Requires use of continuous simulation
hydrologic model
– Use of these models is data intensive and time
consuming
– Lack of knowledge and experience
 Challenge #2: Integrating flow controls
with site design and treatment controls
– How to estimate flow reduction benefits of
other BMPs
– How to estimate treatment capability of flow
control facility
BAHM based on WWHM
 BAHM (Bay Area Hydrology Model) uses
the EPA HSPF computational engine and
WWHM (Western Washington Hydrology
Model) software platform.
 BAHM hydrology parameter values are
derived from locally calibrated
watersheds.
WWHM
 Developed for
the Washington
State Department
of Ecology.
 Used in the 19
counties of
Western
Washington.
BAHM
 Designed for the San Francisco Bay
Area
– Alameda County
– Santa Clara County
– San Mateo County
BAHM
 Components
– user-friendly graphical interface
– automatically loads appropriate parameter
values and meteorological data based on
project location
– uses long-term (30+ year) local precip records
and scales precip based on ratio of project site
MAP and precip gage MAP
BAHM
 Graphical interface: Project Site
BAHM
 Graphical interface: Pre-Project Land Use
– Based on soil, vegetation, land slope, impervious
area
BAHM
 Graphical interface: Project Land Use
– Based on soil, vegetation, land slope, impervious
area
BAHM
 Graphical interface: HMP Facility
– Pond, tank, vault, gravel trench bed, bioretention
BAHM
 Graphical interface: Runoff Analysis
– AutoPond optimizes (minimizes) pond dimensions
to meet HMP flow duration criteria
BAHM
 Calibration of local hydrologic parameter values
– Castro Valley Creek watershed
– Alameda Creek watershed
BAHM
 Comparison of simulated and observed
Castro Valley Creek streamflow
BAHM
 Comparison of simulated and observed
Alameda Creek streamflow
WWHM Application Examples
 Commercial site: Costco store, Woodinville,
WA (14.38 acres)
WWHM Application Examples
 Commercial site: Costco store, Woodinville,
WA (6 acre-feet of underground storage)
WWHM Application Examples
 Planned community: Snoqualmie Ridge,
King County, WA (1,343 acres)
WWHM Application Examples
 Planned community: Snoqualmie Ridge,
King County, WA (10 stormwater ponds
ranging in size from 2 to 20 acre-feet)
Conclusion
 BAHM will facilitate compliance with
HMP and design of flow control facilities
in the Bay Area by providing:
– An easier, standardized way to do
continuous simulation modeling
– A means to compute flow control benefits
of site design/LID and treatment measures
– Standardized reporting to assist municipal
staff in design review
For More Information...
Visit our website at:
www.SCVURPPP.org
Click on “New and Redevelopment Related
Products and Reports”