1. Impacts of Low Impact Development (LID) Techniques on Urban Hydrology
Dawit Melaku and Manoj K. Jha
Graduate Student and Assistant Professor; Civil, Architectural and Environmental Engineering; North Carolina A&T State Univ., Greensboro, NC
Introduction
Study Area
• The study area is composed of different land use cover. It constitutes an intense urban infrastructure in the
neighborhood of Georgetown, northern part of the watershed. This urban structures includes residential houses,
apartments and institutions like Georgetown university. There are also roadways, parkways and also federal
buildings. These account approximately 60% of the total land use. parks and vegetation will constitute about 30-
35% of the total watershed area. There is also a local stream that intersects and mixes with Rock Creek river.
• The surrounding area including the study watershed have similar rainfall characteristic as of District of
Columbia’s. According to USGS, the a maximum discharge of 2777 ft3/s has been recorded in 2012 that drained
from more than 63 mi2 area.
Methodology and Results`
• Watershed delineation was performed using ArcGIS by utilizing the digital elevation model (DEM) and contour
map of the city. A Flow direction and flow accumulation were developed which finally led to the delineation of
the contributing area.
• Sub catchment discretization was achieved based on the information of land cover, percent of imperviousness
and soil type, which resulted in a total of 48 subcatchments
• Three stormwater models: Rational Method, HEC-HMS and Storm Water Management Model (SWMM) were
used to estimate the peak discharge and flow volume of stormwater in the watershed subcatchments. Outputs
from Rational method and HMS models were comparted with SWMM outputs for model validation.
• Precipitation data and IDF (Intensity-Duration-Frequency) chart of the study area was obtained from the
National Oceanic and Atmospheric Administration (NOAA)’s website for estimating a design storm in
simulation.
• Four types of LIDs: bioretention cells, infiltration trench, rain gardens, and porous pavements were
implemented individually and in combination throughout the watershed to evaluate the impact on peak
discharge and runoff volume.
• A cost-benefit analysis was conducted to develop a trade-off relationship between LID implementation cost and
associated benefits in reducing peak discharge and runoff volume in the watershed.
• SWMM: Peak discharge at the outlet of the watershed was found to be 282 ft3/s and the total volume was
2,081,000 ft3. The variation of the hydrographs is shown in Fig. 4 where the peak flow as well as the
volume increases from 62 ft3/s (upstream point 1), 133 ft3/s (midstream point 2) to 282 ft3/s (downstream
point 3).
• HEC-HMS: A relatively higher peak discharge than that of the SWMM. Peak flow at the downstream
section 3 was found to be 291 ft3/s and the total volume of runoff was found to be 2,988,216 ft3 (Fig. 5).
• Compared with SWMM, HEC-HMS output produced a higher magnitude in peak flow and volume of
runoff. This could be due to the fact that HEC-HMS behaves well in pure natural channels than pipe
(conduit) network while SWMM performed better in urban drainage systems.
1
2
3
(3)(2)
(1)
Fig. 4. SWMM Rainfall - runoff hydrograph distribution across the subcatchments; (1) upstream section, (2) mid-
stream section & (3) downstream end
0
10
20
30
40
50
60
70
80
90
100
0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00 3:00
Flowincfs
Time
(1)
-10
10
30
50
70
90
110
130
150
0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00 3:00
Flowincfs
Time
(2)
Flowincfs
Time
0
50
100
150
200
250
300
0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00 3:00
(3)
(3)
(1)
(2)
Rational method produced the highest subcatchment peak discharge of 35 ft3/s. In contrast, SWMM and
HEC-HMS produced 20 ft3/s and 25 ft3/s of peak discharge respectively (above figure).
Land Cover
Legend
Study Area
NHDWaterbody
NHDFlowline
SoilPly
SLOPE
0
B
C
D
Soil Type
Imperviousness
Fig. 3. Watershed delineation and Subcatchment discretization
• Development of cities involves intensive use of land and design of the urban infrastructures, which create more
impervious area leading to substantial increase in peak and quantity of stormwater runoff.
• Substantial increase in peak discharge and runoff volume will potentially cause downstream flooding, accelerate
channel erosion, and impair aquatic habitat.
• Low Impact Development [LID] is an approach to land development that minimizes the impacts of urbanization
in stormwater generation. Some of the the widely used practices (also evaluated in this study) are bioretention
cells, infiltration trenches, vegetative swales, rain gardens and porous pavements (Fig. 1).
Study Objective
Evaluate the effects of implementing LIDs on peak discharge and runoff volume of stormwater in an urban water
system through application of a mathematical model. We applied Storm Water Management Model (SWMM)
developed by U.S. Environmental Protection Agency (EPA) in Dumbarton Watershed located in Metropolitan
Washington, D.C.
Fig 1. Typical residential LID (Source: www.innvoyze.com)
Fig 2. Ariel view of the Dumbarton Watershed and surrounding area
Fig. 5. HEC-HMS Rainfall - runoff hydrograph distribution across the subcatchments; (1) upstream section, (2)
mid-stream section & (3) downstream end
0
5
10
15
20
25
30
35
40
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48
Swmm_Q (cfs)
Rathional_Q (cfs)
Hec-Hms_Q (cfs)
Impacts of LIDs
• The rational method produces higher peak
discharge in comparison with the other two
methods. The SWMM model gives a smallest
value of peak discharge and volume of runoff
where as the HEC-HMS gives a median
result.
• Performing hydrological modeling using three
independent methods can a good pseudo-
validation approach to estimate peak flow and
volume of runoff in cases where field data is
limited or not available.
• LIDs can significantly reduce the volume of
runoff, in this case by more than 30%.
However the impact of LIDs in reduction of
peak discharge is almost negligible.
• Integration of LIDs can be an essential tool in
minimizing the overall cost. The cost-benefit
analysis proves that a trade-off can be applied
to select a relatively optimal range of flow.
Integration of LIDs
PeakDischarge,CFS
Subcatchment ID
Conclusion
![Impacts of Low Impact Development (LID) Techniques on Urban Hydrology
Dawit Melaku and Manoj K. Jha
Graduate Student and Assistant Professor; Civil, Architectural and Environmental Engineering; North Carolina A&T State Univ., Greensboro, NC
Introduction
Study Area
• The study area is composed of different land use cover. It constitutes an intense urban infrastructure in the
neighborhood of Georgetown, northern part of the watershed. This urban structures includes residential houses,
apartments and institutions like Georgetown university. There are also roadways, parkways and also federal
buildings. These account approximately 60% of the total land use. parks and vegetation will constitute about 30-
35% of the total watershed area. There is also a local stream that intersects and mixes with Rock Creek river.
• The surrounding area including the study watershed have similar rainfall characteristic as of District of
Columbia’s. According to USGS, the a maximum discharge of 2777 ft3/s has been recorded in 2012 that drained
from more than 63 mi2 area.
Methodology and Results`
• Watershed delineation was performed using ArcGIS by utilizing the digital elevation model (DEM) and contour
map of the city. A Flow direction and flow accumulation were developed which finally led to the delineation of
the contributing area.
• Sub catchment discretization was achieved based on the information of land cover, percent of imperviousness
and soil type, which resulted in a total of 48 subcatchments
• Three stormwater models: Rational Method, HEC-HMS and Storm Water Management Model (SWMM) were
used to estimate the peak discharge and flow volume of stormwater in the watershed subcatchments. Outputs
from Rational method and HMS models were comparted with SWMM outputs for model validation.
• Precipitation data and IDF (Intensity-Duration-Frequency) chart of the study area was obtained from the
National Oceanic and Atmospheric Administration (NOAA)’s website for estimating a design storm in
simulation.
• Four types of LIDs: bioretention cells, infiltration trench, rain gardens, and porous pavements were
implemented individually and in combination throughout the watershed to evaluate the impact on peak
discharge and runoff volume.
• A cost-benefit analysis was conducted to develop a trade-off relationship between LID implementation cost and
associated benefits in reducing peak discharge and runoff volume in the watershed.
• SWMM: Peak discharge at the outlet of the watershed was found to be 282 ft3/s and the total volume was
2,081,000 ft3. The variation of the hydrographs is shown in Fig. 4 where the peak flow as well as the
volume increases from 62 ft3/s (upstream point 1), 133 ft3/s (midstream point 2) to 282 ft3/s (downstream
point 3).
• HEC-HMS: A relatively higher peak discharge than that of the SWMM. Peak flow at the downstream
section 3 was found to be 291 ft3/s and the total volume of runoff was found to be 2,988,216 ft3 (Fig. 5).
• Compared with SWMM, HEC-HMS output produced a higher magnitude in peak flow and volume of
runoff. This could be due to the fact that HEC-HMS behaves well in pure natural channels than pipe
(conduit) network while SWMM performed better in urban drainage systems.
1
2
3
(3)(2)
(1)
Fig. 4. SWMM Rainfall - runoff hydrograph distribution across the subcatchments; (1) upstream section, (2) mid-
stream section & (3) downstream end
0
10
20
30
40
50
60
70
80
90
100
0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00 3:00
Flowincfs
Time
(1)
-10
10
30
50
70
90
110
130
150
0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00 3:00
Flowincfs
Time
(2)
Flowincfs
Time
0
50
100
150
200
250
300
0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00 3:00
(3)
(3)
(1)
(2)
Rational method produced the highest subcatchment peak discharge of 35 ft3/s. In contrast, SWMM and
HEC-HMS produced 20 ft3/s and 25 ft3/s of peak discharge respectively (above figure).
Land Cover
Legend
Study Area
NHDWaterbody
NHDFlowline
SoilPly
SLOPE
0
B
C
D
Soil Type
Imperviousness
Fig. 3. Watershed delineation and Subcatchment discretization
• Development of cities involves intensive use of land and design of the urban infrastructures, which create more
impervious area leading to substantial increase in peak and quantity of stormwater runoff.
• Substantial increase in peak discharge and runoff volume will potentially cause downstream flooding, accelerate
channel erosion, and impair aquatic habitat.
• Low Impact Development [LID] is an approach to land development that minimizes the impacts of urbanization
in stormwater generation. Some of the the widely used practices (also evaluated in this study) are bioretention
cells, infiltration trenches, vegetative swales, rain gardens and porous pavements (Fig. 1).
Study Objective
Evaluate the effects of implementing LIDs on peak discharge and runoff volume of stormwater in an urban water
system through application of a mathematical model. We applied Storm Water Management Model (SWMM)
developed by U.S. Environmental Protection Agency (EPA) in Dumbarton Watershed located in Metropolitan
Washington, D.C.
Fig 1. Typical residential LID (Source: www.innvoyze.com)
Fig 2. Ariel view of the Dumbarton Watershed and surrounding area
Fig. 5. HEC-HMS Rainfall - runoff hydrograph distribution across the subcatchments; (1) upstream section, (2)
mid-stream section & (3) downstream end
0
5
10
15
20
25
30
35
40
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48
Swmm_Q (cfs)
Rathional_Q (cfs)
Hec-Hms_Q (cfs)
Impacts of LIDs
• The rational method produces higher peak
discharge in comparison with the other two
methods. The SWMM model gives a smallest
value of peak discharge and volume of runoff
where as the HEC-HMS gives a median
result.
• Performing hydrological modeling using three
independent methods can a good pseudo-
validation approach to estimate peak flow and
volume of runoff in cases where field data is
limited or not available.
• LIDs can significantly reduce the volume of
runoff, in this case by more than 30%.
However the impact of LIDs in reduction of
peak discharge is almost negligible.
• Integration of LIDs can be an essential tool in
minimizing the overall cost. The cost-benefit
analysis proves that a trade-off can be applied
to select a relatively optimal range of flow.
Integration of LIDs
PeakDischarge,CFS
Subcatchment ID
Conclusion](https://image.slidesharecdn.com/6307784e-fb8b-4811-a15f-e096ecd77614-150429192248-conversion-gate02/85/Evaluation-Of-Low-Impact-Developments-LID-1-320.jpg)
