In SWMM the model cannot distinguish between roof area and road area. 100% roof area corresponds to 64% of the impervious area at the Grefsen plateau and 465 LID-modules. Dis-connection of 64% of the impervious area equals a fraction of total disDis-connection of 22% in model A and 32% in model B. Before implementation of LIDs the total disconnected area was 65% and 50% for respectively models A and B. After implementation of LIDs the total dis-connected area has increased to 87% and 82% for models A and B. With this approach, the disconnected area is comparable larger with model B than A as illustrated in figure D.4
Figure D.4: Distribution of road and rooftop area on each side of the routing line. 100%
LID as illustrated in the lower figures covers more than the roof area in model B, while in model A not all the rooftop area is covered by the LID, even though the same amount of the LID-modules have been used
In the results below, 25% LID indicate that the LID-modules (BRC and RB) receives water from an area equivalent to 25% of the roof area in the catchment. Because of the initial routing, the implementation of 25% LIDs in model setup A results in a total roof disconnection of 64%
and 66% in model setup B. The ratio DCIA/TIA in model A have decreased from 0.35 to 0.29, while in model B from 0.5 to 0.42. So 25% in the plots below is the same as 64% in for model
setup A and 66% in model setup B.
D.5.1 Continuous rainfall
The regression line in the following plots shows an average reduction in the discharge peaks caused by the LIDs.
The difference between the BRC II and BRC III is not noticeable for the continuous rainfall for model A or model B, even for 25% disconnection or 100% disconnection as shown in figures D.5 and D.6.
The average discharge peaks can be reduced with respectively 5% (y = 0.95x) and 19% at AK52 for 25% BRC and 100% BRC with model A.
Figure D.5: Simulations of the discharge peaks with BRC of 25% and 100% for two types, BRC II and BRC III, against simulations with no LIDs (scenario 0). The regression line represents the mean discharge magnitude at AK52 after the LIDs are implemented in model A.
The average discharge peaks can be reduced with respectively 11% (y = 0.89x) and 28 % at
AK52 for 25% BRC and 100% BRC with model B.
Figure D.6: Simulations of the discharge peaks with BRC of 25% and 100% for two types, BRC II and BRC III, against simulations with no LIDs (scenario 0). The regression line represents the mean discharge magnitude at AK52 after the LIDs are implemented in model B.
The rain barrels (RB) are implemented in the same way as the BRCs. In model A, the average reduction in the discharge peaks are 18% for 100% and 7% for 25% RB for AK52 as shown in figure D.7. Model B, see figure D.8, reduce the average discharge peaks with 26% for 100%
RB and 8% for 25% RB for AK52.
The disconnection of downspouts is implemented with the re-routing option in SWMM (sub-section 4.5). In the setup of disconnection of roof area, the connected road area before imple-mentation of LIDs is assumed the same after the impleimple-mentation. The total disconnection is of that reason larger for model A than B, since model A initially has a higher disconnection rate than model B.
In model A, the average discharge peaks are reduced with 23 % for 100% RD and 13% for 80%
RD at AK52.
Figure D.7: Left: The LID measures RD for 80% (upper) and 100% (lower) roof disconnection at the Grefsen plateau. Right: Simulations with RB where 25% (upper) and 100% (lower) of the connected roof areas are disconnected with rain barrels. The reduction in the discharge peaks at AK52 with model A.
In model B, 100% RD gives an average reduction of 24 % on the discharge peaks at AK52. And 80% RD gives a mean reduction in the discharge peaks of 13%.
Figure D.8: Left: The LID measures RD for 80% (upper) and 100% (lower) roof disconnection at the Grefsen plateau. Right: Simulations with RB where 25% (upper) and 100% (lower) of the connected roof areas is disconnected with rain barrels. The reduction in the discharge peaks at AK52 with model B.
The largest reduction in one model is not the same as for the other one. In model A, 100%
RD gives the largest reduction of 23% followed by 100% BRC with 19%. In model B, 100%
BRC gives largest reduction of 28% followed by 100% RB of 26%. The range of reduction in discharge peaks for 100% disconnection at AK52 is 18-23% for model A and 24-28% for model B.
At Jupiterjordet, where all the sewer system is CSS, the percent reduction in discharge peaks for the LIDs is higher. The wastewater from the householders is not included in the discharge.
Therefore, the percentage average reduction is only for stormwater. In figure D.9, the average reduction in the discharge peaks are 15% with 25% BRC and 63% with 100% BRC with model A. No difference between the BRCs is found in model A. In model B, there is a slightly small difference for BRC II and BRC III, where BRC III gives the largest reduction (see figure D.10).
Figure D.9: Simulations of the discharge peaks with BRC of 25% and 100% for two types, BRC II and BRC III, against simulations with no LIDs (scenario 0). The regression line represents the mean discharge magnitude at Jupiterjordet after the LIDs are implemented in model A.
Figure D.10: Simulations of the discharge peaks with BRC of 25% and 100% for two types, BRC II and BRC III, against simulations with no LIDs (scenario 0). The regression line repre-sents the mean discharge magnitude at Jupiterjordet after the LIDs are implemented in model B.
In figure D.11, disconnection of 25% of the roof area with RB gives an average reduction in discharge peaks of 16% in model A. When all of the roof area is disconnected, 100% RB, the average discharge peaks is reduced with 63 %. In model B an average reduction in the discharge peaks of 18% is observed for 25% RB and 67% for 100% RB (see figure D.12). The measures with 100% RB, 100 % BRC II and 100% BRC III have almost the same average reduction in the discharge peaks for model A and B.
The 80% RD gives a reduction in the average discharge peaks with 46 % for model A (see figure D.11). For 100% RD the regression line has a slope of 20, indicating a reduction of 80%. The coefficient of determination, R2, is however very low. Therefore, the effects of the 100% RD is more uncertain. In model B, a 33% reduction in the discharge peaks is observed for 25% RD and a 60% reduction for 100% RD as shown in figure D.12.
Figure D.11: Left: The LID measures RD for 80% (upper) and 100% (lower) roof disconnec-tion at the Grefsen plateau. Right: Simuladisconnec-tions with RB where 25% (upper) and 100% (lower) of the connected roof areas are disconnected with rain barrels. The reduction in the discharge peaks is for Jupiterjordet with model A.
Figure D.12: Left: The LID measures RD for 80% (upper) and 100% (lower) roof disconnec-tion at the Grefsen plateau. Right: Simuladisconnec-tions with RB where 25% (upper) and 100% (lower) of the connected roof areas are disconnected with rain barrels. The reduction in the discharge peaks is for Jupiterjordet with model B.
At Jupiterjordet, model A has the largest reduction for 100% RD. In model B, 100% BRC II, 100% BRC III and 100% RB give almost equal reduction of 64-68% in the discharge peaks.
D.5.2 Design rainfall
The simulations of a 5-year rainfall for model A are plotted in figure D.13 and for model B in figure D.14.
In AK52 and Jupiterjordet, model A has the lowest discharge peak with 100% RD. On the other hand, model B has the lowest discharge peak for 100% BRC and 100% RB.
The effects from BRC and RB are almost equal in both models. This is the reason for the pink solid line (100% BRC) is almost hidden by the green solid line (100% RB).
Figure D.13: Discharge in AK52 (upper) and Jupiterjordet (lower) during a 5-year rainfall with model A. The dotted red line in the upper plot, at AK52, represents discharge where CSOs occurs.
Figure D.14: Discharge in AK52 (upper) and Jupiterjordet (lower) during a 5-year rainfall with model B. The dotted red line in the upper plot, at AK52, represents discharge where CSOs occurs.
At AK52, LID implementation has largest effect in terms of reducing the peak magnitude and volume in model B compared to model A with BRC and RB. This is shown in table D.7. The number in the table can be read as, with 100% RD in model A the discharge peak from 5-year rainfall is reduced to 68% of the initial peak (the peak from scenario 0).
Table D.7: Relative comparison of the discharge (% Discharge peak ) and volume of water above the overflow weir (% Volume) at AK52 for a 5-year rainfall with model A and model B.
5-year rainfall at AK52
Model A Model A Model B Model B
Scenario % Discharge
To more easily distinguish between the relative reductions in the discharge peak at Jupiterjordet, the relative comparison is made in table D.8.
Table D.8: Relative comparison of the discharge (% Discharge peak) in manhole 172350 for a 5-year rainfall and a 20-year rainfall for the different scenarios presented in the study.
5-year rainfall at Jupiterjordet
Model A Model B
Scenario % Discharge peak % Discharge peak
Scenario 0 100 100
The reduction in discharge peak and volume at AK52 and at Jupiterjordet is decreasing for a 20-year rainfall compared to the 5-year rainfall. And 100% RD gives the largest reduction in the discharge for model A in outlet AK52 and Jupiterjordet, see figure D.15. The lowest reduction
in the discharge is found for 25% BRC and 25% RB. The LID giving the highest reduction is associated with the measure giving the largest reduction in the volume (see tables D.9 and D.10).
Figure D.15: Discharge at AK52 (upper) and Jupiterjordet (lower) during a 20-year rainfall.
The dotted red line in the upper plot, AK52, represents discharge where CSOs occurs.
The 20-year rainfall creates some numerical unstable results, as a consequence of the large runoff created inside each subcatchment. This comes into sight at Jupiterjordet between the time 15:15 and 15:45. As for the 5-year rainfall, 100% BRC and 100% RB give the largest reduction in the discharge in model B and 25% BRC and 25% RB give least reduction. To distinguish the difference in the performance of BRC and RB, see tables D.9 and D.10.
Figure D.16: Discharge at AK52 (upper) and Jupiterjordet (lower) during a 20-year rainfall.
The dotted red line in the upper plot, AK52, represents discharge where CSOs occurs.
Table D.9: Relative comparison of the discharge (% Discharge peak) and volume of water above the overflow weir (% Volume) at AK52 for a 20-year rainfall with model A and B for the different scenarios presented in the study.
20-year rainfall at AK52
Model A Model A Model B Model B
Scenario % Discharge
Table D.10: Relative comparison of the discharge (% Discharge peak) at Jupiterjordet for a 20-year rainfall with model A and B for the different scenarios presented in the study.
20-year rainfall at Jupiterjordet
Model A Model B
Scenario % Discharge peak % Discharge peak
Scenario 0 100 100
Table D.11: Table of values used for 25% and 100% connection of the rooftops to bio-retention cells. Number of units is number of bio-retention cells in the subcatchment. % of impervious area treated is the fraction of impervious area (buildings and roads) contributing with runoff to the bio-retention cells. New % impervious area is the new fraction of imperviousness since parts of the total area is decreased due to occupation of bio-retention cells. The area of the bio-retention cell is 13.1 m2.
LID setup bio-retention cells
Table D.12: Table of values used for 25% and 100% disconnection of the rooftops to rain barrel. Number of units represents number of rain barrels in each subcatchment. %impervious area treated is the fraction of impervious area where the runoff is caught by the rain barrel, until it is full. When the rain barrel is full, the overflows are distributed on the pervious area.
Each rain barrel occupies 0.4 m2.
LID setup for rain barrel
The RD does not have any parameters, because the re-routing option is used. In this way, the exact fraction of DCIA/TIA depends on the initial DCIA/TIA and cannot be set before the model is validated. RD is done for 80% roof disconnection and 100% roof disconnection.
Table D.13: Fraction of impervious area disconnected to the outlet in each subcatchment for 100% and 80% disconnection of rooftops, when it is assumed that already 55% of the rooftops are disconnected. 55% of rooftops already disconnected implies that 82% of the road area is disconnected at all time.
MODEL A
Roof Disconnection (RD)
Subcatchment PctRouting for 100 % RD PctRouting for 80% RD
T161143 95 81
Table D.14: Fraction of impervious area disconnected to the outlet in each subcatchment for 100% and 80% disconnection of rooftops, when it is assumed that already 55% of the rooftops are disconnected. 55% of rooftops already disconnected implies that 82% of the road area is disconnected at all time.
MODEL B
Roof Disconnection (RD)
Subcatchment PctRouting for 100 % RD PctRouting for 80% RD
T161143 84 69
Figure E.1: The contribution from the CSS at the Grefsen plateau (161146) and the wastewater system from Grefsenkollen (297077). The simulation is from a 5-year rainfall with model setup A.
Figure E.2: The contribution from the CSS at the Grefsen plateau (161146) and the wastewater system from Grefsenkollen (297077). The simulation is for a 5-year rainfall with model setup B.
Figure E.3: Calibration process at AK52. Illustrates the pulsing of water into AK52 when the groundwater exponents, B1 and B2, are 0.75 for A1 and A2 of 1.
Figure F.1: The spatial distribution of the slopes in the catchment in degrees. The green color represent flat areas and red represent steep areas.
Figure F.2: Map of the different catchment used in present and previous study of Grefsen and the investigation of CSOs at AK52
The spatial storage capacity in September 2017 at Grefsen can be seen in figure G.1. During the CSOs event at Grefsen in September 2017, the storage capacity was low. The subsurface storage capacity is compared to the maximum simulated value in the reference period 1981-2010 using HBV-model.
Figure G.1: Four pictures with the storage capacity of the subsurface calculated with HBV-model from NVE. The pictures can be seen at SeNorge.no. The pictures are generated at the same time of the date, 07:32, based on interpolated weather observations. Grefsen is labeled northwest for the label Oslo. Data owner is The Norwegian Water Resources and Energy Directorate (NVE)
Figure H.1: Photo of a stormdrain in Waldemar Thranes gate in Oslo. It illustrates the fact that some stormdrains can be exposed to clogging. Photo: Ina Storteig
Figure H.2: Photo of Grefsenveien 21.09.2018 (left) and 21.05.2019 (right). The photos are taken against north and is approximately at the boarder of the catchment. Photo: Ina Storteig
Figure H.3: Photo of where the stormwater sewer from the catchment comes out. During CSO events, the pipe transports diluted wastewater. Photo: Ina Storteig
Figure I.1: A drawing of the conduits at AK52. The picture is from Oslo VAV and is published with permission from Oslo VAV.