analysis of low impact development (lid) strategies using fully-integrated fully-distributed surface...

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

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)

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

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)

GSFLOW: Cascading Flow Paths

Accumulated flow

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)

LIDs: GSFLOW Conceptualization

Manabe (1969) type reservoir • Implemented into the GSFLOW code

• Distributed on a cell-by-cell basis

• Simple design, yet powerful


Manabe (1969) type reservoir

input



D Drainage (specified rate, scheduled rate, or dependent on

model state)

D



D Drainage

E Evaporative loss

E

D



D Drainage

E Evaporative loss

Q Overflow

E

D

Q



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 >𝑺𝒎𝒂𝒙

LIDs: Green Roofs

E

Q

E>0, Q>0, D=0

(CVC & TRCA, 2010)

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)

LIDs: Rain Barrels and Cisterns

Q

E=0, Q>0, D>0

D

LIDs: Infiltration Galleries, etc.

Q

Trenches, and Chambers, and Soakaways

E=0, Q>0, D=K

K

(CVC & TRCA, 2010)

LIDs: Retention Ponds

E>0, Q=0 (Smax=∞), D>0

D

E

LIDs: Detention Ponds

E>0, Q>0, D>0

D

E

Q

LIDs: Underground rain harvesters

Q

E=0, Q>0, D=D(t)

(CVC & TRCA, 2010)

D(t)

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)

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’

Case Study: Seaton Lands

• Complex hydrogeology: 3 Aquifers day-lighting along Duffins Creek

• Extensive wetland connectivity and riparian zones

A A’

Case Study: Seaton Lands – Current Land use

Case Study: Proposed Development

Case Study: Predicted Drawdown no LIDs (m)

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.

Case Study: Infiltration Gallery

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

Case Study: Predicted Drawdown (m)

Case Study: Predicted Drawdown with LIDs (m)

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

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

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

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

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

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

analysis of low impact development (lid) strategies using fully-integrated fully-distributed surface...

Environment