I/I Analysis & Water Balance Modelling Presented by Paul Edwards
Contents Background Wet Weather Model Calibration Inflow / Infiltration Assessment Flow Containment Options Water Balance Model 20 Year Continuous Simulations
Background A Sewer network model of Kilmore was built & calibrated in 2008. In 2010 Victoria experienced its 5 th wettest year on record. Wet weather flows far higher than those predicted by the model. Flows to Kilmore WWTP exceeded storage capacity. A 10 week flow survey was undertaken in September November 2010.
Catchment Description Covers approx 4 km2 and contains 54 km of sewers. Sewers range from 100mm to 375mm 1800 Residential Connections
Flow Survey 6 Flow Monitors & 2 Rain gauges 3 September to 12 November 2010
WWF Calibration A tail or trailing limb observed on the wet weather response. To replicate this the use of the Ground Infiltration Model (GIM) was required. GIM Below ground hydrology to represent delayed rainfall induced infiltration. Antecedent conditions critical.
WWF Calibration Flow Survey Data Blue Trace Model Data Red Trace
WWF Calibration WMF Meter
WWF Verification WMF Meter
I / I Analysis The I/I assessment was undertaken running the calibrated model for the entire 2010 period. RDII volume was calculated for each flow monitor catchment. For comparison the same annual rainfall simulation was undertaken using the much drier year of 2009.
I / I Analysis Wet Weather Flows Orange Trace RDII Volume Fast response & GIM Dry Weather Flown Only Blue Trace
I / I Analysis FM Catchment RDII (2009) RDII (2010) FM1 4% 7% FM2 3% 15% FM3 1% 6% FM4 3% 10% FM5 1% 4% FM6 2% 9%
Flow Containment Assessment Future models created for 2013, 2018 and 2028 development levels. Models run with 5yr Design events Initial Soil Saturation level for Design Events? Assess long term soil saturation levels for a period of 9 years. Rainfall and evaporation series created for 2002 to 2010. 50 th percentile value used as soil saturation level for design events.
Long Term Soil Saturation Daily Soil Store Saturation 80% 70% 60% FM06 FM03 FM05 FM04 FM02 FM01 Long Term Average 2010 Average 50% Saturation (%) 40% 30% 20% 10% 0% May-02 Mar-03 Jan-04 Nov-04 Sep-05 Jul-06 Apr-07 Feb-08 Dec-08 Oct-09 Aug-10 Time
Flow Containment Results Kilmore not 1 in 5 year Compliant
Flow Containment Options I/I Reduction Option Baseline (No I/I Reduction) FM1 & FM2 Catchments - 15% I/I Reduction FM1 & FM2 Catchments - 30% I/I Reduction FM1 & FM2 Catchments - 45% I/I Reduction FM1, FM2 & FM4 Catchments -45% I/I Reduction Total Catchment Spill Volume (kl) 420 315 198 121 42
Flow Containment Options Conveyance Upgrades
Flow Containment Options Conveyance Upgrade + 15% I/I Removal
Flow Containment Options Conveyance Upgrade + 30% I/I Removal
Flow Containment Options Conveyance Upgrade + 45% I/I Removal
Water Balance Model Water balance model developed of Kilmore WWTP Assess inflows, irrigation volumes and potential discharges to Kilmore Creek. Lagoon based treatment system. WWTP does not discharge to a waterbody. Treated effluent irrigated via a central pivot irrigation system. Each component explicitly modelled in InfoWorks CS
WWTP Layout 2 Winter Storage Lagoons Irrigation Pasture 6 Treatment Lagoons
Kilmore Water Balance Model Central Pivot Irrigation Overflow To Creek 2 Winter Storage Lagoons Calibrated Sewer Model 6 Treatment Lagoons
Model Layout
Lagoon Modelling Direct Rainfall Evaporation Catchment Inflows Seepage
20 Year Data Set 1971 1991 Rainfall and Evaporation series created. Evaporation applied using 0.8 pan evaporation factor. Potential irrigation requirement was simulated by applying the evaporation as rainfall to the irrigation pasture. A variable speed pump modelled to extract flow from the winter storage lagoons to replicate the irrigation requirement.
Simulating Irrigation Requirement (Daily Evaporation x 0.75 (crop factor)) (Daily Rainfall x 0.7 (effective rainfall factor)) = Net Evaporation
20 Year Simulations The water balance model was simulated with a range of model configurations e.g. I/I reduction, 2028 development etc. GVW has planned for future increases in irrigation area and winter storage. Proposed WWTP upgrades incorporated into the water balance model. Effects on flows and discharges to creek assessed.
Holistic Assessment Central Pivot Irrigation Overflow To Creek 2 Winter Storage Lagoons Catchment Inflows 6 Treatment Lagoons
20 Year Simulation Results Model Configuration Development Level Volume to Irrigation (ML) Volume discharged to Creek (ML) No. Discharges to Creek Baseline 2011 8652 462 8 102 hectare Irrigation Area 15% I/I Reduction (FM1& 2) 30% I/I Reduction (FM1& 2) 45% I/I Reduction (FM1& 2) 45% I/I Reduction (FM1, 2 & 4) 2011 8729 376 7 2011 8496 405 7 2011 8335 352 5 2011 8166 308 4 2011 7873 237 4 Baseline 2028 9023 853 9 Upgrade to 160 hectare Irrigation Area Upgrade to 160 hectare Irrigation Area & 407.6 ML Winter Storage 2028 9208 613 8 2028 9638 96 2
Summary Project highlights risk of using models calibrated during very dry periods. Gross under estimation during wet periods!!! I/I assessment undertaken over long period. (1 Year of rainfall). Using GIMS with Design Storms. Essential to make soil saturation estimate over long period. I/I reduction alone not enough to make 1 in 5 Year compliant. I/I reduction not cost effective solution. No guarantee of that required level of I/I would be achieved. InfoWorks good platform to undertake water balance modelling. Results showed that planned WWTP upgrades will achieve discharge compliance.