2. Mangatawa catchment consents for earthworks, storm water ...

Hydraulic Modelling: Mangatawa Drain/Maranui Swale - Mitigation Options
Table of Contents
1 Project Description.................................................................................................1
1.1 Introduction.................................................................................................................. 1
1.2 Background ................................................................................................................. 1
1.3 Mangatawa Flood Risk and Stormwater Management ............................................... 3
1.4 Outlet Options Considered .......................................................................................... 3
1.5 Floodway Concepts..................................................................................................... 5
2 Model Studies .........................................................................................................6
2.1 Modelling Stage........................................................................................................... 6
2.2 Hydrological Assessment ............................................................................................ 8
2.3 Rainfall......................................................................................................................... 8
2.4 Hydraulic Model......................................................................................................... 10
2.5 Results....................................................................................................................... 11
3 Proposed Flood Risk Mitigation Measures ........................................................15
3.1 Increased Drain Storage............................................................................................ 15
3.2 Top Spill Stop Bank................................................................................................... 15
3.3 Maintenance Work in Mangatawa Drain ................................................................... 16
3.4 Bruce Road Barrier / Bund ........................................................................................ 16
3.5 Lower Rail Bridge Embankment Stability .................................................................. 16
3.6 Flood Bypass from Maranui to Mangatawa............................................................... 16
3.7 Lower Mangatawa Drain Works ................................................................................ 17
3.8 Sandhurst Culvert...................................................................................................... 17
3.9 Extension of Maranui Culvert .................................................................................... 17
3.10 Maranui Deepening ................................................................................................... 17
3.11 Stormwater Treatment Wetland Area........................................................................ 17
4 Conclusions ..........................................................................................................18
Appendices
Appendix A – Mangatawa Drain Layout Plan
Appendix B – Mangatawa Drain Layout Option 2
Appendix C – Runoff hydrographs
Appendix D – Longsection of hydraulic grade line
Appendix E – Proposed Lower Mangatawa Drain and Maranui treatment area
Beca // 17 March 2009 // Page ii
3932036 // NZ1-1604459-15 0.15 Rev A