For more information about us and what we do feel free to stop by our website at http://earthfx.com/

1. Analysis of Low Impact Development
(LID) Strategies using Fully-Integrated
Fully-Distributed Surface
Water/Groundwater Models
Mason Marchildon
Earthfx Inc.
IAH 2012 Congress
September 18, 2012

2. Ground water and Surface-water FLOW
GSFLOW:
• Based on the USGS PRMS and MODFLOW
• Released in 2008
• Free and open source
• Modular
• Fully distributed
(Markstrom et.al., 2008)

3. GSFLOW Spatial Conceptualization
Rooftop
Impervious areas &
Depression storage
Pervious area
Tree canopy
(interception)
Micro-topographic
depressions
• Sub-cell components
• Impervious area
• Impervious depression storage
• Pervious area
• Pervious depression storage
• Canopy interception

4. GSFLOW: Cascading Flow Paths
• Allows for a many-to-many
pathway definition
• Runoff and
subsurface/interflow are
routed along these
pathways
• The cascade is continued
until a stream segment
reached or a swale
(depression) is reached
• Cascading flow will infiltrate
downslope if there is
available capacity
(Markstrom et.al., 2008)

5. GSFLOW: Cascading Flow Paths
Accumulated flow

6. Low Impact Development (LID) Strategies
(CVC & TRCA, 2010)
Select examples:
• Rainwater harvesting
• Green roofs
• Bioretention
• Permeable pavement
• Infiltration galleries
• Swales
• Etc.
Means of stormwater management
• Rainfall collection
• Runoff reduction
• Infiltration enhancement
• Evapotranspiration (ET) enhancement
(CVC & TRCA, 2010)

7. LIDs: GSFLOW Conceptualization
Manabe (1969) type reservoir
• Implemented into the GSFLOW code
• Distributed on a cell-by-cell basis
• Simple design, yet powerful

8. LIDs: GSFLOW Conceptualization
Manabe (1969) type reservoir
input

9. LIDs: GSFLOW Conceptualization
Manabe (1969) type reservoir
input

10. LIDs: GSFLOW Conceptualization
Manabe (1969) type reservoir
input

11. LIDs: GSFLOW Conceptualization
Manabe (1969) type reservoir

12. LIDs: GSFLOW Conceptualization
Manabe (1969) type reservoir
D Drainage (specified rate, scheduled rate, or dependent on
model state)
D

13. LIDs: GSFLOW Conceptualization
Manabe (1969) type reservoir
D Drainage
E Evaporative loss
E
D

14. LIDs: GSFLOW Conceptualization
Manabe (1969) type reservoir
D Drainage
E Evaporative loss
Q Overflow
E
D
Q

15. LIDs: GSFLOW Conceptualization
Manabe (1969) type reservoir
D Drainage
E Evaporative loss
Q Overflow
Smax Storage capacity
S(t) Current storage E
D
Q
S(t)
Smax
𝑺 𝒕 = 𝑺 𝒕 − 𝟏 − 𝑬 − 𝑫 − 𝑸|𝑺 𝒕 >𝑺 𝒎𝒂𝒙

16. LIDs: Green Roofs
E
Q
E>0, Q>0, D=0
(CVC & TRCA, 2010)

17. LIDs: Bioswales, Bioretention, etc.
E
Q
Enhanced Grass Swales, Dry Swales, and
Vegetated Filter Strips
E>0, Q>0, D=K
K
(CVC & TRCA, 2010)

18. LIDs: Rain Barrels and Cisterns
Q
E=0, Q>0, D>0
D

19. LIDs: Infiltration Galleries, etc.
Q
Trenches, and Chambers, and
Soakaways
E=0, Q>0, D=K
K
(CVC & TRCA, 2010)

20. LIDs: Retention Ponds
E>0, Q=0 (Smax=∞), D>0
D
E

21. LIDs: Detention Ponds
E>0, Q>0, D>0
D
E
Q

22. LIDs: Underground rain harvesters
Q
E=0, Q>0, D=D(t)
(CVC & TRCA, 2010)
D(t)

23. Additional LID Conceptualization:
Permeable Pavement
Achieved by decreasing the (effective)
percent imperviousness
Roof Downspout Disconnection
Achieved by routing impervious runoff to
(same-cell) pervious area
(CVC & TRCA, 2010)
(CVC & TRCA, 2010)

24. Case Study: Proposed Town of Seaton
• Proposed Town of roughly 70,000 residents
• Currently agriculture and natural areas
• GSFLOW used to test the impact of development and the
mitigative effects of LIDs
A
A’

25. Case Study: Seaton Lands
• Complex hydrogeology: 3 Aquifers day-lighting along Duffins
Creek
• Extensive wetland connectivity and riparian zones
A A’

26. Case Study: Seaton Lands – Current Land use

27. Case Study: Proposed Development

28. Case Study: Predicted Drawdown no LIDs (m)

29. Case Study: Implemented LIDs
• Employment areas: Rooftop capture and 90% of the overflow
being redirected to bioswales;
• Residential, recreational and school areas : Roof-to-lawn
routing of impervious runoff (amount dependent on roof
coverage as a proportion of modelled cell);
• Unlined (leaky) storm water management ponds;
• Infiltration gallery; and
• Road side ditches along rural cross sections as opposed to
serviced roadways.

30. Case Study: Infiltration Gallery

31. Case Study: Infiltration Gallery
• Requires adequate depth to watertable (>2 m)
• Requires a relatively high potential recharge rates (Iroquois
beach deposits 𝐾𝑣 ≅ 1 × 10−7 m/s ≅ 3.3 m/yr)
• Needs to be situated in a topographic low to increase
contributing area

32. Case Study: Predicted Drawdown (m)

33. Case Study: Predicted Drawdown with LIDs (m)

34. Case Study: Reduction in GW Discharge to
Streams due to Development without LIDs

35. Case Study: Improvement on GW Discharge to
Streams & Wetlands with LID mitigation

36. Case Study: Resulting LID-Mitigated Impact to
GW Discharge to Streams & Wetlands

37. Case Study: Conclusions
With LID implementation:
• Groundwater drawdowns were reduced by 86%;
• Groundwater discharge to streams was increased by 42%; and
• Urban runoff generation was reduced by 80%
relative to urban development without LIDs

38. In Summary
• Cascading flow routine can allow for any proportion of
generated runoff to be routed to any LID feature
• Fully-integrated and distributed modeling is required in order
to test the feasibility of specific LID strategies, and their local
impacts
• GSFLOW is Open Source: otherwise this assessment tool
would not have been possible

39. References
Credit Valley Conservation and the Toronto and Region Conservation Authority, 2010. Low Impact Development
Stormwater Management Planning and Design Guide, version 1.0. 300 pp.
Manabe S., 1969. Climate and the ocean circulation 1. The atmospheric circulation and the hydrology of the
Earth’s surface. Monthly Weather Review 97(11). pp. 739-774.
Markstrom, S.L., Niswonger, R.G., Regan, R.S., Prudic, D.E., and Barlow, P.M., 2008. GSFLOW: Coupled ground-
water and surface-water flow model based on the integration of the Precipitation-Runoff Modeling System
(PRMS) and the Modular Ground-Water Flow Model (MODFLOW-2005): U.S. Geological Survey Techniques and
Methods 6-D1, 240 pp.
For more on GSFLOW:
TH1-B: E.J. Wexler, Jacek Strakowski, Dirk Kassenaar, Mason Marchildon, Pete
Thompson & Rich Niswonger. Integrated Groundwater-Surface Water Modelling
with GSFLOW in a Complex Watershed on the Niagara Escarpment
TH2-A: Dirk Kassenaar, Mason Marchildon & E.J. Wexler. Rethinking recharge
For more on Urban Hydrology:
F3-G: Peter J. Thompson & William K. Annable. Characterizing change in baseflow
interactions with urbanization through event-based hydrograph separation
and analysis