An ArcGIS tool to estimate the design hydrograph using the VAPI and WFIUH methods in the District of the Central Apennine

Transcript

1 An ArcGIS tool to estimate the design hydrograph using the VAPI and WFIUH methods in the District of the Central Apennine Antonio Annis, Fernando Nardi University for Foreigners of Perugia

2 OUTLINES 1. Background 2. GIS algorithm A. Hydrobase B. Sub Basins C. WFIUH-SB Basin Width Function WFIUH (VAPI, SCS-CN, VAPI, Weghited Width function, Convolution) 3. Sample applications and calibration 4. Performances and comparison vs standard models 5. Discussion

3 FLOOD RISK ASSESSMENT Synthetic rainfall: Design hyetograph Rainfall-runoff: Design hydrograph Flood routing and hazard mapping Flood zoning: risk mapping PROPOSED WORK An Arc-GIS parsimonious model using largely available input data (DEM, landuse) to estimate the design hydrologic forcing scenario for unguaged basins

4 TOOL 1: HYDROBASE DEM sinks pit filling FLOW DIRECTION FLOW ACCUMULATION Treshold area STREAM NETWORK

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6 TOOL 2: SUBBASINS (TORRENTE ASSINO)

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8 TOOL 3: WFIUH-SB: MODULES 1 BASIN Morphometric parameters 2 WIDTH FUNCTION Flow Length Flow Time Width Function 3 WFIUH Rainfall hyetograph (from historic event or VAPI method) Hydrograph

9 TOOL 3: WFIUH-SB, MODULE 1: BASIN (ASSINO) Area [km 2 ] Perimeter [km] H max [m.s.l.m] H min [m.s.l.m] H mean [m.s.l.m] ΔH [m] Drainage density [km/km 2 ] Basin mean slope [%] Mean channel length [km] Mean channel slope [km]

10 TOOL 3: WFIUH-SB, MODULE 2: WIDTH FUNCTION Times of concentration FLOW LENGTH FLOW TIME V channel = f(slope) V hillslope = f(slope, CN) WIDTH FUNCTION tc (WF) tc (WF)= f(v channel, V hillslope ) tc (Giandotti - Kirpich) tc (G-K)=f(A b,h m,l q )

11 TOOL 3: WFIUH-SB, MODULE 3: WFIUH - VAPI VAPI (Valutazione Piene in Italia) method: Rainfall intensity: it c ( T, t c, y m SZO, SZO) a( T, SZO) ( b( SZO) t ) c m(szo) T =Return time t =Duration of the event c =Climatic Omogeneous Zone y =Mean height m

12 TOOL 3: WFIUH-SB, MODULE 3: WFIUH - Rainfall h t c ( T, t c, y m, SZO) i t c t c Subbasin/Vapi-zone Hyetograph (Rainfall Duration= tc) Design time constant hyetograph

13 TOOL 3: WFIUH-SB, MODULE 3: WFIUH Net rain SCS CN Method Net cumulated Rain at time step t P N, t P P TOT, t TOT, t I I a a P TOT, t =Total cumulated Rain at time step t S I a f (CN) f (S) 2 S P TOT =potential maximum soil moisture retention =Initial abstraction I a

14 WF [-] GIT Geology and Information Technology TOOL 3: WFIUH-SB, MODULE 3: WFIUH Weigthed WF 0,1800 0,1600 WF w, i WF i Pi P mean WF w, i WFi Weigthed width function of i-cell Simple width function of i-cell 0,1400 0,1200 0,1000 Pi Cumulated net rainfall of i-cell 0,0800 0,0600 0,0400 Pmean Spatial Mean net rainfall 0,0200 0, Time [min] Pi P mean f ( SZO, CN) Simple WF Weigthd WF

15 TOOL 3: WFIUH-SB, MODULE 3: WFIUH - Flow Convolution Q( t) t 0 P NET ( ) IUH t d Q n n m1 P m WF nm1

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17 WFIUH VS. RATIONAL METHOD Rational Method Q ( t ) it A Triangular Hydrograph C c c b

18 CALIBRATION Avaiable measurements (2014) 183 Rain gauges 14 Hydrometers avaiable The tool allows to input hystoric hyetograph from rain gauges instead of a synthetic hyetograph of VAPI Method trough a drop-down menu

19 CALIBRATION ASSINO BASIN (169 km 2 )

20 CALIBRATION GALERIA BASIN (153 km 2 )

21 CALIBRATION ANIENE BASIN (1469 km 2 ) Medium size basin Recession limb Hillslope flux Groundwater flow

22 STRENGTHS VS. WEAKNESSES PROs CONs Fast and easy to use Few input and calibration parameters Tailored for design hydrology in small ungauged basins Mimic dishomegenous rainfall events in small-to-big basins by WF rescaling Able to represent/calibrate basin impulsive/real flood events Inherits all cons of: concentrated IUH-based rainfall-runoff methods (no routing and groundwater component) SCS-CN rainfall method Constant spatial/temporal distribution of the rainfall Issues in representing multimodal non-impulsice flood events

23 WHAT NEXT Coding of Large basin module for taking into account the spatial distribution of the climate (considering different return times depending on the climatic zone and stream order) Implementation of a modified version of the WF using simplified algorithms for considering missing physical processes (groundwater flow, soil moisture distribution) Implementation of a event-based hillslope-to-channel erosion and sediment transport model to evaluate the bulking factor in the hydrograph estimation Linking WFIUH with FLO-2D: outputs hydrograph as input for a semplified 2D hydraulic flood routing model

24 THANK YOU