Anhui Huangshan Xin’an River Ecological Protection and Green Development Project Urban First Flush Management Modeling and Design – Technical Report November 2019 ABBREVIATIONS ADB – Asian Development Bank BMP – Best Management Practice CDIA – Cities Development Initiative for Asia HMG – Huangshan Municipal Government HXEPG – Huangshan Xin'an River Ecological Protection and Green DP Development Project PMO – Project Management Office FSR – Feasibility Study Report DI – Design institute KP – Knowledge Product SWMM – Stormwater Management LID – Low Impact Development DP – Detention Pond PRC – People’s Republic of China TRTA – Transaction Technical Assistance CONTENTS 1 Introduction ......................................................................................................................... 1 1.1 Project Background ................................................................................................. 1 1.2 Objective and Purpose of the Assignment .............................................................. 1 1.3 Workscope and Objective ....................................................................................... 3 2 SWMM ................................................................................................................................ 4 2.1 About SWMM .......................................................................................................... 4 2.2 Hydrology Module ................................................................................................... 5 2.3 Hydraulics Module .................................................................................................. 5 2.4 Water Quality Module ............................................................................................. 6 2.5 LID .......................................................................................................................... 6 2.6 Treatment ............................................................................................................... 6 3 Methodology ....................................................................................................................... 7 3.1 Research Area ........................................................................................................ 7 3.2 Underlying Surface ................................................................................................. 7 3.3 Storm Sewer Network ............................................................................................. 8 3.4 Rainfall Condition .................................................................................................. 11 3.5 Stormwater Model of Guguan ............................................................................... 12 4 ANALYSIS UNDER DESIGN RAINSTORM .......................................................................14 4.1 First Flush Stormwater .......................................................................................... 14 4.2 Detention Pond Design ......................................................................................... 19 4.3 Runoff Reduction .................................................................................................. 23 4.4 TSS Concentration reduction ................................................................................ 25 4.5 SENTMENT TRANSPORTATION RATE REDUCTION ........................................ 27 4.6 TSS LOAD REDUCTION ...................................................................................... 29 4.7 Analysis ................................................................................................................ 29 5 ANALYSIS UNDER TYPICAL YEAR .................................................................................31 5.1 Outflow process .................................................................................................... 31 5.2 TSS Concentration................................................................................................ 32 5.3 TSS LOAD ............................................................................................................ 32 5.4 Conclusion and Recommendations ....................................................................... 33 6 SUMMARY AND RECOMMENDATIONS ..........................................................................35 6.1 SUMMARY ........................................................................................................... 35 6.2 RECOMMENDATIONS ......................................................................................... 35 Appendix ...................................................................................................................................37 1 INTRODUCTION 1.1 PROJECT BACKGROUND 1. HMG appointed local consultants to undertake feasibility studies. However due to the insufficient working experience of the local consultants, the project feasibility studies need international supports to design the project with international best practice and innovation. 2. A project preparatory team (TRTA team) has been recruited by ADB for project preparation in December 2018, which has insufficient budget and expertise to undertake supplementary studies. The Concept Paper for the project was approved in Oct 2018 and is attached to this ToR. The composition of TRTA team is described in the concept paper for further reference. 3. The purpose of CDIA intervention is to provide additional project preparation resources and to support the innovative designs in the project, in the fields of watershed water quality modeling, storm water best management practice for urban first flush runoff management, information and communication technologies for urban environmental monitoring and big data analysis, climate change adaptation and mitigation in urban sewerage system upgrade and urban river flood control, and environmental monitoring and emergency response systems for industrial parks. 4. CDIA specialists are to introduce innovative technology and international best practice to support project design and feasibility studies. The final deliverables will be prepared in the form of knowledge products which will have both project specific recommendations and can be used as guidelines for further project design during implementation and for other projects in PRC as well. 5. A CDIA team project coordinator will be provided to offer logistics and coordination support to the CDIA individual specialists (including this position) and will also support liaison with the ADB team, PMO, FSR team, etc., to ensure smooth workflow. 1.2 OBJECTIVE AND PURPOSE OF THE ASSIGNMENT 6. A proposed loan of $100 million from the Asian Development Bank for Anhui Huangshan Xin'an River Ecological Protection and Green Development Project (HXEPGDP) has been included in the 2020 investment pipeline agreed upon between the Government of PRC and ADB. A project preparatory technical assistance (PPTA) for Preparing the HXEPGDP has been proposed to design the project and enhance project readiness. 7. The proposed project impact will sustain economic growth in the Yangtze River Economic Belt (YREB) as envisaged for the YREB Development Plan. The economic and environmental conditions in the upstream of Xin'an River will be improved consequently. The Project has four outputs: (i) Urban and rural point source pollution management will be installed; (ii) Non-point source pollution control will be enhanced; (iii) Green finance mechanism will be piloted; and (iv) Capacity for ecological system and project management will be strengthened. 1 8. Xin'an River is the main drinking water source for 10 million urban and rural residents in downstream areas in Zhejiang Province, and Huangshan city is situated in the upstream region of the Xin'an River Basin. Rapid economic development, urbanization, intensive agriculture production, and the growth of tourism in the area have increased both environmental and ecological pressures across the Xin'an River Basin. Both point sources (urban and rural sewage) and non-point sources (agriculture-based and run-off) have impaired the water safety in Xin'an River. To improve/maintain the level of water quality in the upstream reaches of Xin'an River, Huangshan city is in an urgent need of strengthened water management and sustainable green development. 9. The project area covers the overall Huangshan City including 3 districts (Huangshan District, Tunxi District and Huizhou District) and 4 counties (She County, Yi County, Qimen County and Xiuning County). The Project will upgrade and rehabilitate approximately 660 km of storm water sewers to serve over 400,000 urban population and significantly reducing storm water runoff directly discharged into Xin'an River with approximately 3,000 ton per year COD and 400 ton per year ammonia. The environmental monitoring systems will significantly improve the water and air quality controls, and industrial pollution over the whole urban areas of Huangshan City. The project will improve environmental and health conditions for urban residents, especially for poor households which are about 20% of the urban population. 10. Stormwater discharged from urban areas, especially the first flush from separate storm sewers and overflows from combined sewers, can contribute large pollution loadings to the upstream of Xin'an River. Urban sewerage modeling for planning and incorporating low impact development (LID) measures is essential for urban stormwater management to reduce