Case Area Baseline Report Århus Public Water Utility

Anders Breinholt & Anitha K. Sharma DTU Environment, March 2010

Storm- and Wastewater Informatics Case Area Baseline Report Århus Public Water Utility March 2010

Storm and Wastewater Informatics “SWI” is a strategic Danish Research Project with an overall aim to close the knowledge gaps within prediction and control of current and future conditions in integrated urban wastewater systems.

Authors of this Report: Anders Breinholt; DTU Environment Anitha K. Sharma; DTU Environment

In Collaboration with: Århus Public Water Utility

Address: DTU Environment Department of Environmental Engineering Technical University of Denmark Miljoevej, building 113 DK-2800 Kgs. Lyngby Denmark

Phone & Fax +45 4525 1600 & +45 4593 2850

Project Homepage: http://www.swi.env.dtu.dk

Case Area Baseline Report Århus Public Water Utility March 2010

Contents 1. OBJECTIVES WITH THIS DOCUMENT...... 2 2. EXPECTED OUTCOME OF THE SWI PROJECT FROM THE PERSPECTIVE OF ÅRHUS PWU.. 2 3. ÅRHUS PUBLIC WATER UTILITY AND SWI ...... 2

3.1 ORGANISATION...... 2 3.2 FOCUS AREA FOR SWI...... 3 4. THE STORM- AND WASTEWATER SYSTEM OF ÅRHUS...... 6

4.1 THE CATCHMENT AREA...... 6 4.2 SEWERAGE COMPONENTS ...... 7 4.3 WASTE WATER TREATMENT PLANTS ...... 12 4.4 STORM AND WASTEWATER CONTROL STRATEGY:...... 17 5. MAJOR ISSUES AT ÅRHUS PWU...... 18 6. EXISTING SWS MODELS AND MEASUREMENT DATA...... 24

6.1 MODELLING TOOLS...... 24 6.2 MEASUREMENTS...... 26 7. SWI RELEVANT PROJECTS IN THE CASEAREA ...... 27

7.1 INTEGRATED CONTROL OF ÅRHUS PWU...... 27 7.2 EARLY WARNING OF WATER QUALITY ...... 33 7.3 WEATHER RADAR CONTROL OF SEWER SYSTEMS...... 35 REFERENCES...... 36 APPENDIX 1. DETAILS ABOUT THE PLANNED/IMPLEMENTED FILLING AND EMPTYING STRATEGY OF EXISTING AND PLANNED STORAGE TANKS IN MARSELISBORG NORTH CATCHMENT AREA...... 39

Case Area Baseline Report Århus Public Water Utility March 2010

1. Objectives with this document

The objectives with the “Case Area Baseline Report” are to:

- Give an introduction to the Storm- and Wastewater System (SWS) managed by År- hus Public Water Utility (PWU) - Describe relevant issues of Århus PWU that relate to the research project SWI - Give an overview of the future integrated control plans with the SWS - Provide references to more comprehensive literature.

This report will thus benefit both the SWI Management Group and the Work package Lead- ers in planning the overall work for the coming years and benefit the researchers/students who will be involved with the SWI project.

2. Expected outcome of the SWI project from the perspective of Århus PWU

According to Århus PWU the expected outcomes of the SWI project are1: - Ability to make now- and forecasting of rain with a “needed and sufficient” accuracy in spatial and temporal resolution. - Illustration of real-time modelling and control of integrated and optimized operation of sewerage system and WWTP for minimisation of damages (in a broad context: flooding, pollutant emission, resource consumption). - The potential of controlling discharge points i.e. discharging less polluted wastewater (thin wastewater) to streams or lakes before mixed with heavily polluted wastewater. Thin wastewater is defined by concentration of N, P, COD and E-Coli. - At least 1 case that illustrates improved performance by simulations at a level of con- fidence sufficient to convince plant owners and other stakeholders to proceed with demonstration in practical real life. - Come up with solutions that contribute to safe hygienic water quality2 in Lake Brabrand, Århus Å and Århus harbour. - Ideas for retainment/handling of first flush in the wastewater system.

3. Århus Public Water Utility and SWI

3.1 Organisation

The Public Water Utility of Århus called “Vand og Spildevand” politically and administratively belongs to the Århus municipal authority under the “Division of Technique and Environment”. The total turnover of “Vand og Spildevand” is 500 mio. DKK and has 220 employees. The re-

1 Answers are based on the questionnaire (Århus Municipality, 2009b) and the material received following the interview 2 Hygenic water quality only meets the requirements for E-coli specified by the bathing water directive.

Case Area Baseline Report Århus Public Water Utility March 2010 sponsibilities of PWU Århus are Drinking Water supply, transportation and treatment of wastewater (30-35 mio. m3/year) and urban runoff for approx. 300.000 inhabitants (Århus Municipality, 2008a).

3.2 Focus Area for SWI

The total area of Århus Municipality is approx. 525 km2 (35 x 15 km). Figure 3.1 is a map of Århus municipality and the red rectangle shows the selected area (enlarged on the right hand side in the figure) for the research activities of SWI project. Århus PWU have recently launched a plan for a new integrated control strategy (Århus Municipality, 2008b) in this area following the wastewater plan 2006-2009 of Århus Municipality (Århus Municipality, 2005) with the aim to optimise the existing and planned SWS in order to achieve hygienic water quality standard in Århus harbour and Lake Brabrand, because it poses the greatest integrated control potential and is also the focus area for the integrated control project called In- tegrated Control of Århus PWU (see chapter 7.1 and 7.2).

Figure 3.1: The border of Århus Municipality shown with a thick black line to the left. Adap- ted from (Krüger & Århus Municipality, ??)

The storm and wastewater system of Århus is going through drastic changes in these years and one of them is centralization of wastewater treatment in order to save operating costs.

Case Area Baseline Report Århus Public Water Utility March 2010

Figure 3.2 gives an overview of the existing WWTP in Århus municipality and future of these WWTPs. As seen from this figure there are 14 WWTPs in Århus municipality and according to this figure centralization of wastewater treatment would ultimately result in 2 large WWTP namely Marselisborg and Egå. This will result in an estimated savings in operational costs by 40% or 29 mil DKK/year (Århus Municipality, 2005). The economic calculus behind the cen- tralisation showed that the close-down of the smaller WWTP´s (all except Viby and Åby) would save the citizens 6-9 mil DKK/year. The focus area of this report consists of the three large WWTP’s namely Viby, Åby and Marselisborg and according to figure 3.2. Viby and Åby WWTP will also be closed down after the end of their expected lifetime, which is after 2017. (Århus Municipality, 2005). Egå will as a starting point, not be considered in SWI context, since this is not in the focus area of SWI.

Figure 3.2: Planned stepwise closedown of treatment plants in Århus Municipality (Århus Municipal- ity, 2005) Figure 3.3 shows location of the three recipients Lake Brabrand, Århus Å and Århus harbour, where the most significant overflows/outlets are discharged in the focus area.

Case Area Baseline Report Århus Public Water Utility March 2010

Figure 3.3: Lake Brabrand, stream of Århus (Århus Å) and Århus harbour. Lake Brabrand and stream of Århus are highlighted with blue color.

Case Area Baseline Report Århus Public Water Utility March 2010

4. The Storm- and Wastewater system of Århus

4.1 The catchment area

The catchment area in focus for SWI project and the integrated control project include the catchments surrounding Lake Brabrand, the stream of Århus Å and the Århus harbour and is devided into 3 subcatchments: Åby, Viby and Marselisborg as shown in figure 4.1 (Århus Municipality (2009a; 2008b) and (Krüger & Århus Municipality, XXXX) . The upper left catchtment in the figure is Åby catchment with a total catchment area of 1638 ha and drains to Åby WWTP (Åby RA). The lower left catchment is Viby catchment with a total area of 1543 ha and drains to Viby WWTP (Viby RA). The catchment to the right in Figure 4.1, is Marselisborg catchment draining to Marselisborg WWTP (Marselisborg RA), and is the largest of the 3 subcatchments with a total area 2173 ha and consists primarily of combined sewer system. Table 4.1 shows the total catchment area, reduced area, combined sewer area and separate sewer area of these 3 catchments areas.

Figure 4.1: The Storm- and Wastewater system of Århus showing combined catchment, separate catchment, future urbanization, position of the three WWTPs (Marselisborg, Viby and Åby) with their design capacity expressed in PE, position of radar and position of the 6b rainguages. (Bassø 2008 and modified).

Case Area Baseline Report Århus Public Water Utility March 2010

Table 4.1: Type and area of the three sub catchments of interest of SWI project: Marselisborg, Viby and Åby. (Århus Municipality, 2009b)

Århus AREA COMBINED SEPARATED Total Reduced Total Reduced Total Reduced CATCHMENT [ha] [ha] [ha] [ha] [ha] [ha] Marselisborg 2178 791 1139 562 1030 229 Viby 1543 706 607 228 925 475 Åby 1638 621 642 206 992 413 Total 5359 2118 2388 996 2947 1117

4.2 Sewerage components

4.2.1 Åby catchment The southern part of Åby catchment is the most interesting with respect to research and is explained below. For a complete overview of Åby catchment, see (Krüger, 2008b). Figure 4.2 shows the location of main pipes, overflow structures, pumping stations and existing and planned storage tanks in the southern part of Åby catchment. This catchment consists of 4 pumping stations transporting wastewater to either Åby or Viby WWTP where the water is treated before discharged to the stream of Århus Å. There is one storage basin with 2000 m3 situated in the lower right part of Figure 4.2 at “Åby Vest” pumping station. The current pumping stations capacity is 470 l/s. The figure further shows that, there are numerous overflow structures in this catchment area. The planned efforts in this catchment to reduce overflows to Lake Braband and the stream of Århus are described below.

Planned efforts to reduce overflows to Lake Braband: Following efforts are planned to reduce the number of overflows to Lake Braband:  The pumping capacity at “Åby Vest pumping station will be will soon be increased by 335 l/s, and a new control strategy (see figure 4.3) will be applied where 470 l/s can be directed to Åby WWTP as it is today and the rest 335 l/s to Viby, which is not possible today. It is expected that the number of overflows to Lake Brabrand by this will be reduced from 4 to 1-2 per year. (Århus Municipality, 2009a).  Construction of 3 storage basins near Lake Brabrand to be in operation by 2011 with storage capacities of 445 m3, 700 m3 and 1450 m3 Århus Municipality (2009a). This action is expected to reduce overflows to the Lake Braband from the 15 weirs to one overflow per basin per second year.  Implement separate sewer system in some areas of Braband, which might affect the size of the above mentioned planned storage tanks.  Some of the overflow structures will be closed down or changed to internal overflows.

Planned efforts to reduce overflows to the stream of Århus: Following efforts are planned to reduce the number of overflows to the stream of Århus:

Case Area Baseline Report Århus Public Water Utility March 2010

(450 m3) (1450 m3)

(700 m3)

Figure 4.2: The SWS of southern part of Åby (mid-left part of Figure 4.1) showing location of main pipes, structures, pumping station and volumes of existing and planned storage tanks (Krüger, 2008b). The volumes 445 m3, 700 m3 and 1450 m3 shown in parentheses are the actual volumes of planned storage tanks (Århus Municipality (2009a)).

Figure 4.3: New control strategy of Åby Vest pumping station (see more in (Århus Municipality, 2009a)).

Case Area Baseline Report Århus Public Water Utility March 2010

 Construction of 1 storage tank at Åby WWTP before 2011 with a storage capacity 9.200 m3 to reduce the number of overflows to the stream of Århus Å from currently 59 to 2-3 per year (Århus Municipality, 2009a).  Some of the overflow structures will be closed down or changed to internal overflows.

4.2.2 Viby catchment Figure 4.4 show a major part of Viby catchment, for a detailed overview of Viby catchment see Krüger (2008b).

(1300 m3)

(15000 m3)

Figure 4.4: The SWS of Viby (from the lower left part of Figure 4.1) showing the main pipes, structures, pumping stations and storage basin. (Krüger, 2008b). The volumes 1300 and 15000 m3 shown in parentheses are the volumes of planned storage tanks according to (Århus Municipality (2009a)).

The Viby catchment consists of two pumping stations transporting wastewater to Viby WWTP. There are 4 storage tanks (only 3 are shown in the figure and the 4th not shown in figure is situated the south-western part of the catchment) with 160 m3, 800 m3, 800 m3, 330 m3 (not shown on figure) storage capacity. Furthermore it is planned to construct 2 new storage tanks; one next to Viby WWTP with a capacity of 15.000 m3 and the other planned stroge tank is Stavtrup bassin with a capacity of 1.300 m3 (Århus Municipality, 2009a). A

Case Area Baseline Report Århus Public Water Utility March 2010 project is also looking at the possibility of separating the catchment of Stavstrup instead of construction of the Stavstrup bassin. The storage tank at Viby WWTP is expected to de- crease the number of overflows from 55 to 4-5 per year and the Stavtrup bassin is expected to reduce number of overflows to Døde Å from currently 121 per year to 2 per year. The figure further shows that some overflow structures will be changed to internal overflows.

4.2.3 Marselisborg Catchment Wastewater from Marselisborg catchment is transported to Marselisborg WWTP. The catchment is divided into Marselisborg catchment North and Marselisborg catchment south and are explained in brief below.

4.2.3.1. Marselisborg Catchment North

Figure 4.5 shows the sewer system of the northern part of Marselisborg catchment.

Figure 4.5: The SWS of Marselisborg north. The main pipes, structures and pumping stations are shown. Adapted from (Krüger, 2008a)

This catchment consists of 4 storage tanks and 2 new storage tanks will be constructed by 2011. The existing tanks are: Risskov (325 m3), Trøjborg (16.000 m3), Filmbyen (3.600 m3)

Case Area Baseline Report Århus Public Water Utility March 2010 and Mølleparken (1.500 m3) and the planned storage tanks are at Carl Blochs gade (15.700 m3) and Havnens (3.200 m3) (Århus Municipality, 2009a). Appendix 1 explains briefly the expected/planned filling and emptying of the existing and planned storage tanks.

Flushing of pipes along Århus Å Flushing of pipes along Århus Å is conducted once a day for minimising or eliminating the emptying of existing sandfilters at Åboulevarden at the north side of P49030K and to avoid sluicing of the pipe every 14th day (for more details see Århus Municipality, 2009a).

4.2.4 Marselisborg catchment South Figure 4.6 shows the southern part of Marselisborg Catchment with its 3 existing storage tanks: Skåde Skole basin (500 m3) and Morvad basins (3000 m3 + 600 m3) and will be sup- plemented by 2 new storage tanks most probably at Marselisboulevarden and near Marselis- borg WWTP. There are 2 pumping stations and 2 throttles in connection with the Morvad storage tank.

Figure 4.6: The SWS of Marselisborg south. The main pipes, structures and pumping stations are shown. Adapted from (Krüger, 2008a)

Case Area Baseline Report Århus Public Water Utility March 2010

4.3 Waste Water Treatment Plants WWTPs in the SWI focus area have undergone many changes since their construction and as mentioned earlier the sewer and wastewater system in Århus municipality is going through drastic changes, which will presumably result in further changes in the operation of WWTPs during SWI project. This report gives a brief overview of the three WWTP (Åby, Viby and Marselisborg).

4.3.2 Åby WWTP Figure 4.7 shows a photo of Åby WWTP taken from Google earth. Åby WWTP consists of mechanical, biological with sidestream hydrolysis and chemical treatment units and has a design capacity of 83000 PE BOD. The biological treatment is based on Biodenipho principle and is practice achieved by advanced online control based on DIMS. The hydraulic inlet capacity of the plan is 2.800 m3/h and hydraulic capacity to the biological treatment is 1.800 m3/h. Treated wastewater and overflows are discharged to the stream of Århus. Table 4.2 gives details about design details of Åby WWTP. Table 4.3 shows requirements and achieved effluent concentrations for important parameters for 2008. A new retention tank will be built next to the plant with a volume of 9.200 m3 and a disinfection step will be added to reduce E-Coli concentrations in outlet.

Table 4.2. Design details of Åby WWTP. (Pedersen (2010)) Flows Max flow, inlet 2800 m3/h Max flow, inlet biology 2800 m3/h Volumes Sand and grease 380 m3 Primary tanks - m3 Bio P tanks * 3990 m3 Aeration tanks 17.200 m3 Secondary clarifiers 11.500 m3 Digester 1300 m3 *Side stream hydrolysis in 50%

Case Area Baseline Report Århus Public Water Utility March 2010

Figure 4.7 Photo of Åby WWTP taken from Google Earth

Table 4.3: Outlet permissions and actual discharge in 2008 for WWTP Åby. (Pedersen, 2010) Parameter Requirement Discharge in 2008 Unit (Average) COD 75 21,5 mg/l

BOD5,mod 10 1,24 mg/l

SS 20 2,48 mg/l Total-N 8 2,49 mg/l

NH4-N . Max 8 - mg/l

NH4-N 2 0,16 Summer (mg/l)

NH4-N 4 0,05 Winter (mg/l) Total-P 0.4 0,28 mg/l

Total-P 7,1 3,35 Kg/d

O2 60 65 % of saturation pH 6.5-8.5 - Min-max

Viby WWTP Figure 4.8 shows a photo of Viby WWTP taken from Google earth and figure 4.9 gives an overview of the processes. Viby WWTP consists of mechanical, biological and chemical

Case Area Baseline Report Århus Public Water Utility March 2010 treatment units and has a design capacity of 84000 PE BOD. The biological treatment is based on recirculation principle and in practice achieved by advanced online control based on DIMS. Treated wastewater is discharged to the Århus stream. Table 4.4 gives desing details about Viby WWTP. Table 4.5 shows requirements and achieved effluent concentrations for important parameters for 2008.The plant was recently extended with two new settling tanks to increase hydraulic capacity by 4810 m3 resulting in a total capacity of 15170 m3. There is a storage basin of 2.000 m3. The future plans at this WWTP are: 3  Additional storage basin with a capacity of 15.000 m  disinfection step to reduce E-Coli concentrations in outlet to 1000 E.coli/100 ml  Establishment of a new outlet pipe from Viby WWTP to “Århus Å “with a minimum capacity of 600 l/s.

Table 4.4. Design details of Viby WWTP. Pedersen (2010)) Flows Max flow, inlet 4896 m3/h Max flow, inlet biology 4896 m3/h Volumes Sand and grease 400 m3 Primary tanks 4050 m3 Bio P tanks 3300 m3 Aeration tanks 11450 m3 Secondary clarifiers 15170 m3 Digester 5200 m3

Case Area Baseline Report Århus Public Water Utility March 2010

Table 4.5: Outlet permission and actual discharge in 2008 for WWTP Viby. ( Pedersen( 2010)). Parameter Requirement Discharge in 2008 Unit (Average) COD 75 20,9 mg/l

BOD5,mod 15 1,28 mg/l SS 20 2,49 mg/l Total-N 8 4,20 mg/l

NH4-N . Max 8 - mg/l

NH4-N 2 0,25 Summer (mg/l)

NH4-N 4 - Winter (mg/l) Total-P 0.4 0,25 mg/l Total-P 4.30 0,25 Kg/d

O2 60 - % of saturation pH 6.5-8.5 85 Min-max

Figure 4.8 Photo of Viby WWTP taken from Google Earth

Case Area Baseline Report Århus Public Water Utility March 2010

Figure 4.9: Process overview of WWTP Viby

Marselisborg WWTP Marselisborg WWTP is the largest WWTP in Århus Municipality with a design capacity of 200.000 PE BOD. Figure 4.10 shows a photo of Marselisborg WWTP taken from Google earth. The biological treatment is based on Biodenitro principle and in practice achieved by advanced online control based on DIMS. Treated wastewater is discharged to the Århus Bay. Table 4.6 gives design details about Marselisborg WWTP. Table 4.7 shows requirements and achieved effluent concentrations for important parameters for 2008.Recently Marselis- borg was extended with a sand filter (Århus Municipality, 2009c) to remove more phospho- rous and the hydraulic capacity increased through an expansion of the secondary settling tanks. If hydraulic load increases above 1400 l/s wastewater is bypassed to well no. 8 and to outlet pipe.

Table 4.6. Design Details of Marselisborg WWTP. (Pedersen 2010) Flows Max flow, inlet 5040 m3/h Max flow, inlet biology 4320 m3/h Volumes Sand and grease 800 m3 Primary tanks 7160 m3 Bio P tanks - m3 Aeration tanks 16000 m3 Secondary clarifiers 21800 m3 Digester 6000 m3

Case Area Baseline Report Århus Public Water Utility March 2010

Table 4.7: Outlet requirement and discharges in 2008 for Marselisborg WWTP(Pedersen (2010)) Parameter Requirement Discharge in 2008 Unit (Average) COD 75 32,8 mg/l

BOD5,mod 15 2,14 mg/l SS 30 3,70 mg/l Total-N 8 4,38 mg/l Total-P 0.8 0,40 mg/l Total-P 20,8 10,39 Kg/d

Figure 4.10 Photo of Marselisborg WWTP taken from Google Earth

4.4 Storm and Wastewater control Strategy:

The current strategy of the storm and wastewater is simply to forward as much water as possible to the WWTP irrespective of biological capacity. The pumping stations, couple of storage tanks (explained before) and some overflow structures are controlled and monitored, however there is no control interaction between WWTP and sewer system.

All the 3 WWTP have installed control strategies, where return sludge is controlled based on sludge blanket level for dry and wet weather (for more details see Lynggaard & Lading (2006); Lynggaard et al. (2009)). The control strategy is installed at Åby and Viby WWTP using a sludge volume sensor but is not installed at Marselisborg, because the supplier has de-

Case Area Baseline Report Århus Public Water Utility March 2010 cided to remove the sensor from production. However, at present there is no prognosis of in- fluent volumes to the WWTP, and hence no lead time to change from dry weather control to wet weather control or to store water in the sewer system. A detailed discussion about control strategy and possibilities is presented in chapter 7.

5. Major issues at Århus PWU

The Storm- and Wastewater management at Århus PWU is faced with many challenges because of (see further details in the sections below):

 “Service check” of the Danish Water Sector  Political wish for bathing places and Recreational utilization of Lake Brabrand, stream of Århus and Århus harbour  EU Bathing Water Directive  The Water Framework Directive  Functional practice of storm- and wastewater systems under rainy conditions  Urbanisation  Climate change

Service check of the Danish Water Sector The overall target with the Service Check, an Act that will come to force by 1st of January 2010, is to secure a more effective water sector in Denmark, i.e. cutting costs. In Århus, the first action will be, pursuant to the new law to centralize the WWTPs, which is explained in section 3.3.

Political wish for bathing places and Recreational utilization of Lake Brabrand, stream of Århus and Århus harbour

The political wish for bathing water quality in the Harbour area of Århus has been the main driver behind the investments in the SWS for the past 4 years and investments are also expected in future. Figure 5.1 show how bathing water quality is defined according to EU Direc- tive, (2006).

Case Area Baseline Report Århus Public Water Utility March 2010

Figure 5.1: Water Quality definitions according to the EU Bathing Water Directive (EU Directive, 2006).

Figure 5.2 gives an overview of the bathing water quality along the Århus bay and shows that bathing water quality along the Århus bay was satisfactory or above except in case of Egå, where it is poor (Århus Municipality, 2009d) .

Case Area Baseline Report Århus Public Water Utility March 2010

Figure 5.2: Public bathing places around Århus. (Århus Municipality, 2009d)

Table 5.1 shows the status of the three recipients Lake Braband, Stream of Århus and Århus Harbor in 2005 and the targets (Scenario 2B) set by Århus PWU (Århus Municipality, 2009a). The chosen efforts to reach the targets are listed below (Bassø, 2008).

 Expansion of total storage volume: 54.000 m3  Disinfection of CSO from one basin in the sewer system and 1 basin at Viby WWTP  Disinfection of treated wastewater at two WWTP´s: Viby and Åby, which accounts for account for half of the flow in Århus Å.  Construction investments: 340 mils DKK  Reduction of overflow structures from 195 to 133  Reduction of overflow from 1.69 mil. m3 to 0.4 mil. m3  Integrated control solutions of WWTP, sewer system and recipient

Case Area Baseline Report Århus Public Water Utility March 2010

Table 5.1: Comparison of the status of various parameters before (2005) and after the Århus Å project (2009) (Århus Municipality, 2009a). Assessment criteria Lake Brabrand Stream of Århus Århus Harbour Water quality Satisfactory Poor Poor Water sports possible Yes No No

aesthetic aspects unacceptable unacceptable unacceptable Status 2005 Algaes ( Secchi depth) <1 m <1 m >1 m Poor, but vastly Excel- Water quality Good/Satisfactory improved lent/Satisfactory Water sports possible Yes Yes Yes

Aesthetic aspects Improved Vastly improved Improved (Scenario 2B) Status in 2009 Status in 2009 Algaes ( Secchi depth) Unchanged Unchanged Unchanged

Recent water quality measurements from Lake Brabrand and Århus Harbour show satisfactory/excellent results, whereas results from the stream of Århus show poor quality. This shows that the efforts to improve the water quality made so far have already given good results at many places and it is expected that the ongoing efforts and future efforts, some of which are listed in this report, will result in achieving the goals at the remaining places (Bassø, 2008).

The vision of Århus Municipality is that Lake Brabrand and the stream of Århus should offer people recreational amusements like canoeing (Figure 5.3). The stream of Århus has been exposed again (used to be cased) and the surrounding areas are now popular urban spaces (See Figure 5.4).

Case Area Baseline Report Århus Public Water Utility March 2010

Figure 5.3: Canoeing at the stream of Århus Å is one of the visions behind the investments in better water quality. (Århus Municipality, 2006).

Figure 5.4: The green areas surrounding Århus Å is an attractive lung of the city.(Århus Municipality, 2006)

EU Bathing Water Directive

The EU Bathing Water Directive (EU Directive, 2006) demands that a warning system be set up that evaluate the future bathing risk. This is being developed as a part of Integrated Con- trol of Århus PWU (see chapter 7 for further details) by DHI with expected operation by 2011 (Århus Municipality, 2008b).

Case Area Baseline Report Århus Public Water Utility March 2010

The Water Framework Directive It is expected that the Water Framework Directive will imply more stringent requirements to the water quality in Lake Brabrand (Århus Municipality, 2008b) because the area was selected as an EU habitat area. However with the initiatives taken to secure clean bathing water quality by Århus PWU will presumably meet the stricter requirements of the Water Frame- work Directive (Bassø, 2008). Further, the consequences of Water plan (Vandplan) on mu- nicipalities are not yet known.

Functional practice of storm and wastewater system under rainy conditions The minimum requirements to the SWS are governed by a document called “Skrift 27” from Spildevandskomiteen under the Society of Danish Engineers (Spildevandskomiteen, 2005). The major requirements are (Århus Municipality, 2005):

 Basement flooding: no more often than once per second year  Terrain flooding: from combined areas: no more than once every 10th year from separated areas: no more than every 5th year  Total P discharge: to Lake Braband: 11.3 t P/year to the Stream of Århus: 18.6 t P/year

Urbanisation It is expected that the city of Århus will grow with 75.000 PE over the next 25 years and the paved area will expand. The Harbor area is being developed with many new apartments and workplaces which will enhance the demand for clean aesthetic seawater. The planned development of the harbour area is visualized in Figure 5.5.

Figure 5.5: The planned harbour expansion in Århus. www.debynaerehavnearealer.dk/forside.asp

Case Area Baseline Report Århus Public Water Utility March 2010

Climate change It is expected that climate change will induce 20-40% more heavy rainfall and this is ac- counted for by multiplication of rainfall input by a climate factor of 1.2 when designing the future SWS. Another important factor to include in simulations of future scenarios is the expected sea level rise. According to (Bassø, 2008) expected sea level rise of 50 cm has been used in calculation of future scenarios.

6. Existing SWS models and measurement data

6.1 Modelling tools

Hydrological model A MIKE SHE model (DHI product) was set up in connection with the development of an early warning system for hygienic water quality. MIKE SHE is an integrated hydrological modelling system for building and simulating surface water flow and groundwater flow. The model was used for flow and substance simulation of the grey areas of Figure 6.1.

Sewer model MOUSE models are available for all the three catchment areas, i.e., Marselisborg (one for Marselisborg North and one for Marselisborg South), Viby and Åby catchment; however these are being converted to Mike Urban. These models have been calibrated against measurements in the sewer system. The model of Marselisborg North is calibrated several times compared to the other models and presumably the most reliable one. A merged model of all 4 submodels is seen in Figure 6.2. Most of the newly constructed basins have already been implemented in the mouse models (Århus Municipality, 2009a). In Figure 6.1 the red area is sewer system modeled by simplified MOUSE models calculating flow and substance.

Stream model MIKE 11 (DHI product) is used for flow and substance modelling in both Lake Brabrand and Århus Å indicated by the blue colour in Figure 6.1

Sea model MIKE 21 (DHI product) is a sea model used for flow and substance calculations of the harbour area. Combing all the models makes it possible to forecast the water quality in the harbour and thus the expected hygienic water quality.

Case Area Baseline Report Århus Public Water Utility March 2010

Figure 6.1: The modeling framework used to develop an early warning system for poor bathing water quality. (Krüger & Århus Municipality, XXXX).

Figure 6.2: A recent merged Mouse model of the selected SWS (Århus Municipality, 2009a)

Case Area Baseline Report Århus Public Water Utility March 2010

WWTP model There are no existing models of the treatment plan, however it is planned to make simple additions to the existing Mike Urban models.

6.2 Measurements

A brief overview of the available measurements is given here and for a comprehensive description of available measurement equipments (rain gauges, radar, flow and level-meters as well as sensors at waste water treatment plant) see (DHI, 2007). For details about sensor communication, configuration and control gear systems (PLC, SRO, IFIX , DIMS etc.) see DHI (2007; 2006b).

Rain gauges and radar In 2008 Århus Municipality installed a LAWR weather radar on Edvins Rahrs Vej and is moved to Harlev Wastewater Treatment plant to get better measurements (Figure 6.3 and figure 4.1) in an attempt to obtain a better spatial rainfall description for model input. There are also 6 traditional tipping bucket rain gauges covering Århus quite well as seen on Figure 4.1. Three of the point rain gauges are operated by Spildevandskomiteen (SVK) and three by Århus PWU.

Figure 6.3: LAWR radar installation on Edwin Rahrs vej.

Time series data and calculations of these can be viewed by a thin client (DIMS) coupled to a database called “REGN”. Automatically generated overviews from the database as well as other rain related information is placed on the intranet. The database and the web-site are intended as a place to store future modelling and reporting.

Case Area Baseline Report Århus Public Water Utility March 2010

Flow- and level meters There are flow meters at Jægergårdsgade pumpingstation., Åby Vest pumpingstation and in- flow/outflow at the 3 WWTPs. Most probably more flow and level meters will be installed as these are regarded essential for the intended future control strategy.

Data validation and filtering DIMS has a build-in function with a number of methods for real-time data validation and some of the most general filters to reduce noise is also implemented. More about data validation can be found in (Århus Municipality, 2009a)

WWTP Several parameters are measured and monitored at the 3 WWTPs. Some of these parameters are inlet/outlet flow, return sludge flow, temperature, salinity, sludge volume, sedimentation rate, suspended solids (return and active sludge tanks), sludge level in secondary settler and turbidity in outlet (Århus Municipality, 2009a).

7. SWI relevant projects in the Casearea

As mentioned earlier the SWS of Århus municipality is going through drastic changes and this report gives a brief overview of the SWI relevant projects, which are in progress at the Århus PWU parallel to SWI.

7.1 Integrated control of Århus PWU

The aim with the integrated control strategy that was initialized in 2008 (Århus Municipality, 2008b) is to optimize the utilization of sewer and WWTP capacity in order to minimize pollu- tion to Lake Brabrand, stream of Århus and Århus Harbour focusing especially microbial pol- lution. The long-term objective is to secure hygienic water quality at Lake Brabrand and År- hus Harbour, but not the stream of Århus. The participants are Århus Municipality, DHI, Krüger and PH-Consult. This casereport gives a brief details about the project Integrated control of Århus PWU, whereas the details about goals, planned implementation control system strategy, time schedule etc. are described in danish in Århus Municipality (2008b), Århus Municipality (2009a),

Goals of the integrated control system Some of the goals of the integrated control system are listed below (Århus Municipality, 2008b):

- Minimize CSOs to the recipients especially with respect to safe hygienic water quality - warning of poor bathing water quality for the citizens - Control discharge of CSOs to less vulnerable recipients - Minimize total discharge of nutrients to the recipients - Optimise the utilization of existing storage volume - Secure optimal inlet flow to the WWTP´s

Case Area Baseline Report Århus Public Water Utility March 2010

- Minimize operating costs such as electricity and chemicals - Prevent basement flooding - Maintain a robust and reliable SWS

Implementation of Control System Strategy The control system will consist of two types of control: rule-based and advanced.

The rule-based system will be based on control strategies that are determined from typical rainfall-runoff patterns and will not include on-line modelling. The system is expected to secure hygienic water quality without communication with radar. The rule-based control will serve as back-up for the more advanced control strategy and will be planned, designed and implemented in 2010 for the catchment of Marselisborg, Åby and Viby. Experience with the effect of the rule-based control will form the basis for the magnitude of the advanced control strategy.

The advanced control will take advantage of model predictive control (MPC) using continuous signals from the rain radar to forecast precipitation and effects in the sewer system by on-line modelling. Continuous modelling will thus be used to select the best control strategy in accordance with the conditions listed above.

The advanced control is expected planned, designed and implemented by end of 2010, so that 2011 can be used for potential adjustments. Depending on the milestones of the research projects that Århus Municipality is part of ideas/outcomes hereof may be implemented as part of the advanced control strategy.

Active control will only take place during rainfall. In dry weather basins, pumping stations, overflow structures, and WWTP’s are controlled traditionally as implemented already, by PLC´s and an IFIX head station at Eskelund (see more in Århus Municipality (2009a)).

In case of rain the radar sends its input signals to Mouse on-line that continuously calculate forecasts of flow in the sewer system. At the same time forecasts of maximum hydraulic capacity at the WWTP´s are calculated.

Control matrix and evaluation tool Figure 7.1 shows an example of how targets are ranked in the integrated control implementation project from red (highest) to green (lowest) (For more details see (Århus Municipality, 2009a)). According to this table sludge escape is the most important factor to avoid, whereas basement flooding and good water quality in Lake Brabrand, stream of Århus Å and bathing water quality in the harbor is second important targets.

Case Area Baseline Report Århus Public Water Utility March 2010

Figure 7.1: Control matrix for static rule-based control and model predictive control. The color (red to green) indicates the scale of importance. Adapted from (Århus Municipality, 2009a).

The target for control has to be operationalised at 3 control levels: - Relapse control where the rule-based control is independent of any communication between PLCs and/or SRO system (Århus Municipality, 2009a).

- Overall rule-based control (where it is assumed that information about the state of the system is available for the outlined control strategies).

- Model based control where model simulations of future states form basis for the chosen control set points.

Both in relapse control and overall rule-based control the objectives will solely be used ‘offline’ during evaluation of the different control strategies, whereas in the model based control the objectives will be used ‘online’ in the decision making process at a later stage. In both cases the control objectives will be written as mathematical expressions making automatic optimization of control possible in both off-line and on-line situations.

Case Area Baseline Report Århus Public Water Utility March 2010

Based on the experience and need all the simulated costs like bathing days cost, nutrient discharge, energy, taxes etc can be considered for evaluation of the offline implemented objectives.

In the on-line optimization of the model-based control objectives are incorporated by continuously assessing the risk (probability * consequence) of particular control actions. The dynamic risk analysis will be extended with the experience and research of SWI.

It is important to find an appropriate level of detail for both offline and online implementation of control objectives. Control objectives might change over time and thus the objective matrix will have to be updated and implemented in the evaluation toolbox by Municipality staff.

The offline evaluation tool (model) will be used to evaluate effects of considered control strategies on three control levels: relapse control, rule-based control and model-based control. The offline evaluation tool will both be used in the current optimization project as well as in future evaluation of new projects and renovation of existing system. Figure 7.2 shows how an offline model is used to check strategies to be put to operation and tested in reality.

Figure 7.2: Illustration of offline formulation of control objectives for evaluation of the relapse and rule-based control. Adapted from (Århus Municipality, 2009a).

The online evaluation tool is used for dynamic assessment and optimization of the control strategy for the model-based control level which is believed to be superior to the rule-based strategy in terms of saved costs. Figure 7.3 shows how an offline model is used to check strategies to be put to operation and tested in reality objectives as well as the usage of offline formulation for evaluation.

Case Area Baseline Report Århus Public Water Utility March 2010

The work with identification of control strategies may lead to undesirable long calculation times if data from radars are being used or other heavy data inputs. Therefore it will be necessary to limit the amount of input data during the development of the off-line evaluation tool to describe the relapse control and rule-based control. Final evaluation of the off-line formulation will have to be based on a longer rain period.

Figure 7.3: Illustration of on-line formulation of model predictive control objectives as well as the usage of off-line formulation for evaluation. Adapted from (Århus Municipality, 2009a).

Sensor reliability and uncertainty It is important to secure that calculations and evaluations addresses statistical uncertainties and data reliability. Sensor data from the system will be used to determine set points for a number of control handles in both rule-based and model-based control. Sensor data will have to be interpreted according to sensor type. Radar data are handled specifically while handling of other sensors is more comparable. However, sensor signals can be expressed with a mean and a statistical uncertainty regardless of sensor type. DIMS (DHI product) are used for data validation and ensure the validity of the control strategy and the set points.

Case Area Baseline Report Århus Public Water Utility March 2010

Data will be graduated according to “data creditability” (quality level) which is part of the se- curity level of the chosen control strategy and thus for chosen set points. Data validation could for example expose tendencies in sensor time series implying that a particular sensor weight in the control strategy will have to be reduced correspondingly. See more about data reliability and uncertainty in (Århus Municipality, 2009a).

Integrated control possibilities and limitations An overview of possible objectives/tasks during a rain event for each of the following applica- tion specific systems: weather radar (WR), sewer system (SS) and wastewater treatment plant (WWTP) together with the measurements and control handles available for these systems are given in (Krüger & Århus Municipality, XXXX). Further control possibilities and limitations are discussed below.

Control of sewer systems and increased storage volumes will result in prolongation of period with high hydraulic loads to waste water treatment plant in connection with a rain event. Therefore WWTPs need to have sufficient capacity to cope with longer periods with increased hydraulic load than would be the case without control of the sewer system. Further- more, except from first flush effects the substance load pattern will also change due to increased storage volumes and control of sewer systems. Suspended solids load will be reduced during emptying of the basins due to sedimentation, whereas flushing of basins will give rise to short-term high substance loads of the plant.

The hydraulic capacity of the WWTP is highly dependent on the sedimentation rate in the secondary clarifier, the sedimentation rate is high when the suspended solid load is low and vice versa. During rain the high flow to the WWTP will carry sludge from process tanks to the secondary settler which will increase the hydraulic capacity. The dynamic effect can only be utilized if the secondary settler has a balanced return sludge flow that accounts for the change in sedimentation rate to secure a controlled sludge piling.

The planned integrated control between sewer and WWTP requires that the maximum hydraulic capacity Qbiomax is calculated dynamically. This is equal to being able to estimate the sedimentation rate. This is already installed at Åby and Viby WWTP using a sludge volume sensor but is not installed at Marselisborg, therefore it is necessary to design and implement a methodology for dynamic sedimentation rate estimation (Århus Municipality, 2009a).

One of the ways of reducing high loads to the WWTP is avoiding flushing of upstream storage basins during peak loading, which requires continuous calculation of load estimation. At Marselisborg load estimation is carried out based on moving average value of ammonium concentration from the ammonium sensors in the process tanks multiplied by inlet flow. An- other indication of high load in inlet flow at Marselisborg WWTP is the pumping capacity of primary sludge, which decreases as a result of flushing of storage basins due to high load. Thus pumping capacity could be a useful parameter to use for calculation of current load estimate.

Case Area Baseline Report Århus Public Water Utility March 2010

It is expected that a good flow estimate can be obtained to the inlet pumping station at the WWTP of up to one hour and a more uncertain estimate of 2-3 hours based on measurements of rain (and prediction of rainfall), level- and flow meters, emptying/filling of storage basins, etc (Århus Municipality, 2009a).

The flow estimates can be utilized by WWTP to prepare for high hydraulic loads to switch from dry weather to wet weather operation and vice versa. Feedback of Qbiomax and load estimation from the WWTP to the sewer system will represent the maximum boundary condi- tion for the sewer system. Åby WWTP needs one hour to switch from dry weather to wet weather operation and would thus benefit from one hour prediction of flows (Århus Municipal- ity, 2009b).

Qbiomax will indicate the maximum capacity of the inlet pumps that is controlled by the WWTP (minimum value should be the dimensioning value while maximum is limited by pumping capacity). Decisions about where to overflow or store the water in the sewer in case of full capacity at the WWTP is important in setting up the strategy. An example of local control of basins that are placed at the WWTP´s Åby and Viby could be to adjust the maximum outlet from the basins to the dimensioned Qbiomax subtracted by the inlet flow from pumping station.

The integrated control has been configured as 6 independent systems – 3 WWTP´s and 3 catchments. Communication between catchment of Åby and Viby is necessary because Åby west pumping station can send water to either WWTP.

Viby WWTP can be controlled better if dry weather periods are estimated because the secondary settler can be decoupled and added again during rain events. The decoupling should only take place when four days of dry weather is expected (Århus Municipality, 2009b).

More discussion of possible integrated control options can be found in (DHI, 2006b) and (År- hus Municipality, 2009a).

7.2 Early warning of water quality

This section gives a brief introduction to Early warning of water and for a more comprehensive description of the warning system, see (Århus Miunicipality, 2009a).

Background According to the EU Bathing Water Directive a warning system (EU Directive, 2006) will have to be established at most popular beaches or public swimming facilities before 2011. Initially this warning system will only look at the hygienic water quality and hence the system would be an internal By installing an early warning system Århus Municipality wants to protect its citizens by a bathing ban in case bacteria concentrations are forecasted to exceed criteria. Initially this will only be (I første omgang er det kun hygiejnisk vandkvalitet, så derfor bliver varslingen en intern foranstaltning fra begyndelsen)

Case Area Baseline Report Århus Public Water Utility March 2010

Criteria Rain events with intensities corresponding to return periods of more than four years can be ignored when checking compliance with bathing water criteria. Similarly one event with return period of less than 4 years can also be ignored if citizens are warned in advance (DHI, 2006a).

Figure 7.4: Overflow to the recipients shown with red dots. (Århus Municipality, 2009a)

Figure 7.4 shows where overflows to recipients with potential of violating the bathing water quality are located.

Modelling complex It will be investigated whether a mouse online model can be used in parallel with the recipient models to predict the bacteria concentrations. The warning system will be built on top of models developed during the integrated control project and will consist of the separate tools: Mike11, Mouse and Mike 21. DHI and Krüger is currently working with setting up the model complex. For more information about the warning model, see (DHI, 2006a).

To be able to model overflow/outlet of bacteria the model is fed with different concentrations of E.Coli bacteria corresponding to release type (shown below):

Case Area Baseline Report Århus Public Water Utility March 2010

Wastewater: 43*106 E.coli/100 ml Rainwater: 104 E.Coli/100 ml Treated wastewater from WWTP: 19.000 E.Coli/100 ml Disinfected wastewater 10000 E.Coli/100 ml.

There is a flow- and substance gauge (ACTCP ultra sonic device) installed in Århus Å measuring N, P, PH and conductivity (every half hour). It is calibrated every second week. The Mike 11 model for the stream is calibrated once a day.

Four different warning methods are outlined that all apply to the bathing water directive (År- hus Municipality, 2009a):

1. During “reasonably high” rain intensities - warnings ends 3 days later 2. When overflow has been recorded – warning ends 3 days later 3. When overflow has been recorded – warning ends after time calculated by model 4. When model-calculation of concentrations is to high – warning ends after time calculated using model.

The chosen strategy in Århus is to select the warning method according to the control strategy:

- Relapse control (where the rule-based system is independent of communication between PLC and SRO). Method 2 will be used.

- Rule based control assuming all information about the system states is available for the established control strategies. Method 3 will be used.

- Model based control where model simulations of the future states form basis for the chosen control set points. Method 4 will be used.

For a more comprehensive description of the warning system, see (Århus Municipality, 2009a).

7.3 Weather radar control of sewer systems Weather radar control of sewer systems is another project of SWI relevant, which Århus PWU is taking part. The partners of this project University of Aalborg, Krüger and utilities Aalborg, Egedal, Hvidovre, Odense, Slagelse, Tønder andÅrhus. More information about the project can be found at www.vejrradar.dk.

Case Area Baseline Report Århus Public Water Utility March 2010

References

(Bassø, 2008) Lene Bassø. Slides from presentation at SWI Kick-off meeting in Århus 2008- 11-19.

(DHI, 2006) Hygiejnisk vandkvalitet i Århus havn, Århus Å og Brabrand sø. Katalog over komponenter og standarder for styring og overvågning i afløbssystemet. Ud- arbejdet af DHI, Krüger og Århus Kommune. Projektgruppe 4.

(DHI, 2006a) Hygiejnisk vandkvalitet i Århus havn, Århus Å og Brabrand sø. Beskrivelse af varslingssystem for badevandskvalitet. Udarbejdet af DHI, Krüger og Århus Kommune. Projektgruppe 4.

(DHI, 2006b) Hygiejnisk vandkvalitet i Århus havn, Århus Å og Brabrand sø. Beskrivelse af integreret styring af afløbssystem og renseanlæg. . Udarbejdet af DHI, Krü- ger og Århus Kommune. Projektgruppe 4.

(EU Direktiv, 2006) EUROPA-PARLAMENTETS OG RÅ- DETS DIREKTIV 2006/7/EF. 15. febru- ar 2006. Om forvaltning af badevandskvalitet og om ophævelse af direktiv 76/160/EØF.

(Kildesporing, 2009) Kildesporing i forbindelse med forringet badevandskvalitet, By- og Landskabs- styrelsen, Miljøministeriet, 2009.

(Krüger & Århus Municipality, ??) WSSTP. Urban Pilot Theme 1: Manag- ing rain events and flooding in urban areas. Fact Sheet: Demonstration project Århus, ??

(Krüger, 2008a) Oversigtsplan – oplande til Marselis- borg. Århus Å, samstyring af afløbssy- stem og renseanlæg. 04.11.2008.

Case Area Baseline Report Århus Public Water Utility March 2010

(Krüger, 2008b) Oversigtsplan – oplande til Viby og Åby renseanlæg. Århus Å, samstyring af af- løbssystem og renseanlæg. 04.11.2008.

Lynggaard-Jensen A. and Lading L. 2006 On-line determination of sludge settling velocity for flux-based real-time control of secondary clarifiers. Water Science & Technology, V. 54, No 11-12; PP- 249-256.

Lynggaard-Jensen A. et. Al. 2009 Increased performance of secondary clarifiers using dynamic distribution of minimum return sludge rates. Water Science & Technology, V. 60, No 9; PP- 2439-2445.

(Pedersen, 2010) Description of Åby, Viby and Marselis- borg WWTP.

(Spildevandskomiteen, 2005) Skrift nr. 27. Ingeniørforeningen i Dan- mark – IDA Spildevandskomiteen. Funktionspraksis for afløbssystemer under regn. Oktober 2005.

(Århus Municipality, 2009a) Samstyring af afløbssystem og rense- anlæg - Projekt Århus Å. Århus kommune, Krüger og DHI, Marts 2009.

(Århus Municipality, 2009b) SWI Questions and Answers from År- hus Municipality and subsequent interview. Århus Municipality, February 2009.

(Århus Municipality, 2009c) Årsrapport 2008, Vand- og Spildevand, Teknik & Miljø, Århus Kommune maj 2009.

(Århus Municipality, 2009d) Map from homepage of Århus Munici- pality. http://www.aarhuskom- mune.dk/portal/erh- verv/miljoe/miljoedata/badevandskvalit et

Case Area Baseline Report Århus Public Water Utility March 2010

(Århus Municipality, 2008a) Virksomhedsplan 2009. Århus Vand og Spildevand. Teknik og Miljø. Århus Kommune, December 2008.

(Århus Municipality, 2008b) Opgavebeskrivelse for samstyring af afløbssystem og renseanlæg. Notat udarbejdet af Århus Kommune, Teknik og Miljø, Vand og Spildevand, 2008.

(Århus Municipality, 2006) Bedre vandkvalitet i Brabrand Sø, År- hus Å og Århus havn. Århus Kommu- ne, Teknik & Miljø, Vand og Spilde- vand, 2006.

(Århus Municipality, 2005) Spildevandsplan 2006-2009. Udgivet af Århus Kommune, Miljøkontoret, April 2005.

Case Area Baseline Report Århus Public Water Utility March 2010

Appendix 1. Details about the planned/implemented filling and emptying strategy of existing and planned storage tanks in Marselisborg North Catchment area.

(Århus Municipality, 2009a).

Control strategy for filling and emptying of Storage tanks away from midtown

Trøjborg Storage tank This is an existing storage tank with a storage capacity of 16,000 The filling and emptying strategy of this tank is controlled by the water level in the downstream pipe lying alongside Århus harbour. The strategy secures that mid-town is prioritised in sending wastewater to Jægergårdsgade pumping station. This keeps the water level adequately low preventing in- cidents of basement flooding. Overflows from Trøjborg storage tank are directed to Århus Bay. Just north of the outlet lies one of Århus most popular public bathing facilities “Den permanente”.

Havnens Storage tank This storage tank will be built in the harbour area (Havnens basin) with a storage capacity of (3.200 m3). It is expected that this will reduce overflows from 9 to 2-3 overflows per year per weir. The emptying/filling of the basin at the harbour will be controlled by the water level in the downstream pipe alongside Århus harbour thereby favouring water from mid-town for the same reasons as was the case with the Trøjborg storage tank. This storage tank will have a large impact on the hygienic water quality of the harbour area, thus overflows at Trøjborg will be favoured from overflows alongside the harbour area and Århus Å. Downstream the storage tank a throttle will be placed that limits the maximum hydraulic capacity to 600 l/s.

Control strategy for filling and emptying of Storage tanks in centertown

The plan is to have 3 storage tanks in the mid-town to achieve low water level (avoid flooding of basements) and secure the bathing water quality in the harbour by minimizing overflows to the stream of Århus Å. There are 2 already existing storage tanks (Filmbyen; 3.600 m3) and Mølleparken; 1.500 m3)) and 1 storage tank to be constructed (Carl Blochs gade; 15.700 m3). (Århus Municipality, 2009a).

Filmby basin When the water level in the interception pipe along Århus harbour is higher than in the pipe along Århus Å a throttle (se ovenfor) will close so that the high water level along Århus harbour doesn’t affect the water level along the stream of Århus Å and when the throttle (se ovenfor) closes the filling of the Filmby basin will start with water from mid-town. Ultra-sonic devices are placed in both pipes for measuring the levels. Emptying will start to the interception pipe when Jægergårdsgade pumping station has capacity and when the water level falls sufficiently low in the interception pipe.

Møllepark basin

Case Area Baseline Report Århus Public Water Utility March 2010

The strategy is that as the water level in the pipes at Vesterbro Torv raises or the level in the pipes along the stream of Århus raises the throttle/slides at Vestebro Torv, Ved Immervad and Vester Alle and Åboulevarden closes. Similarly the throttles/slides at Filmby storage tank closes at a given water level. The consequence of this strategy is that the filling of Møllepark storage tank will only occur from a smaller catchment (between Vesterbro Torv and Århus Å) and the water level in the will be kept low at the northern side of stream of Århus.

The emptying of the basin will normally take place to a pipe close to the tank, but there is a possibility of emptying the water to a pipe on the south side of the stream. The pumps used for emptying the storage tanks are used daily to flush the pipes along the stream of Århus in order to prevent sand accumulation in the pipes. For more details about the daily flushing the reader is referred to (Århus Municipality, 2009a).

Carl Blochs Gade basin The construction of the basin at Carl Blochs Gade will reduce the number of overflows to “Århus Å” dramatically from 127 to 2 per year. The area alongside the stream of Århus consists of many building with deep basements and therefore flooding in this area will have quick and huge negative consequences, and hence the control strategy shall secure that basement flooding is avoided. To keep the water level alongside the stream of Århus low the throttles/slides/gates at Vesterbro Torv and Vester Alle are closed, thereby water from the catchment area north and west catchment of Vesterbro Torv and west of Vester Allé is directed to Carl Blochs Gade storage tank. The emptying of the storage tank will be achieved by constructing a new pressure pipe which is connected to the DSB pipe placed at the southern side of the railway. This will relieve a part of hydraulic laod to the Centertown. The water in the DSB pipe is transported by gravity to the pumping station of Jægergårdsgade, and there is risk of discharge to Århus harbour from the DSB pipe. Therefore emptying of the basin can only take place when: - There is no stowage in the DSB tunnel - When the overflow structure O12400S is not overflowing - When the water level in the interceptor pipe along the harbour is not high