School of Geography FACULTY OF ENVIRONMENT School of Geography FACULTY OF ENVIRONMENT GEOG5060 GIS and Environment Dr Steve Carver

School of Geography FACULTY OF ENVIRONMENT Outline: Incorporating time Distributed models Other examples Lecture 9. Hydrological modelling 2: runoff models

School of Geography FACULTY OF ENVIRONMENT Introduction Runoff modelling is time dependent antecedent conditions precipitation ground cover slope length (time to reach channel) channel length (time to reach gauging station) Predict catchment response

School of Geography FACULTY OF ENVIRONMENT Incorporating time Difficult GIS data model not suited to handling time Time-series analysis model response per unit time run sequence of results Model integration link external runoff model with GIS

School of Geography FACULTY OF ENVIRONMENT Distributed models Lumped models: no spatial component example: RUNMOD Distributed models: spatially variable inputs control variables outputs example: TOPMOD

School of Geography FACULTY OF ENVIRONMENT Mass balance models based on estimating relative volumes of inputs and outputs size of stores? Runoff mass balance: RO = (P – Int – ET – SS) + run-on

School of Geography FACULTY OF ENVIRONMENT Implementing a mass balance model Simplified mass balance model: RO = (P – Int – ET – SS) + run-on RO = P + run-on (assuming Int, ET and SS are negligible) P is simulated or known rain guage or radar data Run-on calculated from weighted flow accumulation

School of Geography FACULTY OF ENVIRONMENT Example Simple mass balance model: 1.Create hydrologically correct DEM 2.Calculate flow direction 3.Calculated flow accumulation for time Tn using rainfall Tn as weight grid 4.Determine water volume at pour point for time Tn 5.Repeat steps 3-4 n times

School of Geography FACULTY OF ENVIRONMENT Example: Burnhope Burn

School of Geography FACULTY OF ENVIRONMENT Example: RF and response RF t=1 RF t=2 Response t=1 Response t=2

School of Geography FACULTY OF ENVIRONMENT Example: simulated storm event t=1t=2t=3 t=4t=5t=6

School of Geography FACULTY OF ENVIRONMENT Example: response t=1-6 t=1 t=2t=3 t=4t=5t=6

School of Geography FACULTY OF ENVIRONMENT Example: predicted hydrograph

School of Geography FACULTY OF ENVIRONMENT Question… What problems might there be with such a model?

School of Geography FACULTY OF ENVIRONMENT Time/area response Based on: upstream contributing area (volume estimate) distance from channel (time to peak) used to estimate discharge (Q) at any point on drainage network for given rainfall event use soils, geology and land use data to compensate for effects of: interception, infiltration and percolation throughflow events surface roughness surface storage (puddles - lakes) etc.

School of Geography FACULTY OF ENVIRONMENT A time/area response model Time/area runoff response model: 1. calculate contributing areas and channel lengths 2. derive slopes and channel gradients 3. calculate channel velocities using Manning’s n as follows... V = 1 / n. R 2/3. S 1/2 4. calculate time from channel length and velocity... t = L/V 5. interpolate from channel over catchment 6. use with distributed rainfall data to predict flows

School of Geography FACULTY OF ENVIRONMENT n = , mean channel response time = approx. 3hrs, plus slope runoff times DEMFlow direction Flow accumulation Channel length Mean channel slope Distance to nearest channel

School of Geography FACULTY OF ENVIRONMENT Question… What problems exist with the time/area response model?

School of Geography FACULTY OF ENVIRONMENT Conclusions Not easy to do runoff calculations in GIS time critical spatio-temporal variability of controls calibration/validation issues Two basic examples: mass balance model time/area response model

School of Geography FACULTY OF ENVIRONMENT Workshop Running dynamic models weighted flow accumulation incorporating spatio-temporal variables

School of Geography FACULTY OF ENVIRONMENT Practical Running a GIS-based hydrological model Task: Derive a simple hydrograph from a mass balance model Data: The following datasets are provided… Section of Upper Tyne Valley DEM (50m resolution) and 10m contours River network (1:50,000) Precipitation layers 1 through 6 (simulated)

School of Geography FACULTY OF ENVIRONMENT Practical Steps: 1.Calculate hydrologically correct DEM using flowdirection, sinks and fill 2.Calculate channel response to precipitation using flowaccumulation with the weight_grid option 3.Note maximum flow value 4.Repeat steps 2-3 for each time step 5.Plot maximum flow value vs time

School of Geography FACULTY OF ENVIRONMENT Practical Experience with building and running models Familiarity with functions in Arc/Info for building hydrological response models

School of Geography FACULTY OF ENVIRONMENT Next week… Land suitability modelling Multi-criteria evaluation (MCE) Multi-objective land allocation (MOLA) Examples Workshop: MCE and MOLA Practical: MCE in GRID