7/27/2019 Full Report2
1/15
1. Model Calibration-model represent the real case and essential for accurate flow
resistance forecasting
Model calibration was attempted by simulate the autumn 2000 flood and then verified with
the available recorded information. Based on mannings equation (Equation 1), the floodplain
roughness of the model was adjusted until the simulatedvalue (flood depth and velocity)was fitted well with recorded value (n=0.07).
Equation 1
Table 1.1 shows Mannings value based on Chow, 1959 whilst table 1.2 indicates the
simulated velocity and depth based on trial and error to fit the observed data from farmer A.
Table 1.1: n value for floodplains
Table 1.2: Observed (farmer A) and simulated velocity and depth with different mannings value
Simulated results show good correlations with observed data for Farmer A with n value=0.07(figure 1.1).
Figure 1.1: Good correlation between observed and simulated data
7/27/2019 Full Report2
2/15
Graph 1.1, 1.2 and Table 1.3 illustrates simulated and observed value using recorded datafrom Farmer A, Farmer B and willow.
Graph 1.1: Simulated and observed velocity and depth at farmer A logging equipment at point 384756.847,
243710.625
Graph 1.2: Simulated and observed depth at farmer B CCTV at point 385958.536, 239416.722
Table 1.3: Simulated and observed time that flood water reach tree and time of maximum depth at willow at point
384902.658, 241679.317
-0.5
0
0.5
1
1.5
2
2.5
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0:00:00 4:48:00 9:36:00 14:24:00 19:12:00 0:00:00 4:48:00 9:36:00 14:24:00
Depth(m)
Velocity(m/s)
Time from start of simulation (hh:mm:ss)
Observed Velocity V - calibration run 0.03 V - calibration run 0.04
V - calibration run 0.05 V - calibration run 0.06 V - calibration run 0.07
Observed Depth Depth - calibration run 0.03 Depth - calibration run 0.04
Depth - cal ibration run 0.05 Depth - calibration run 0.06 Depth - cal ibration run 0.07
0
0.5
1
1.5
2
2.5
0:00:00 12:00:00 0:00:00 12:00:00 0:00:00
Observed depth
Depth - calibration run 0.03
Depth - calibration run 0.025
Depth - calibration run 0.04
Depth - calibration run 0.05
Depth - calibration run 0.06
Time into simulation Comment 0.03 0.04 0.05 0.06 0.07
09:10:00 time that flood waters reach tree 08:55:00 09:05:00 09:05:00 09:10:00 09:15:00
14:00:00 time of maximum depth, 2.20 m 12:50:00 13:05:00 13:30:00 13:40:00 13:50:00
7/27/2019 Full Report2
3/15
Figure 1.2: Comparison flood inundation area between satellite image and calibrated model based on autumn
2000 flood events
There is no much different between flood inundation areas for the model based on autumn
2000 flood events with satellite image flood inundation area. With respect to flow depth, flow
velocity and flood area extent, the model is good calibrated to represent the reality.
Figure 1.3 illustrates flood extent, area affected and total volume at different time based on
different return period (50, 100 200). Based on the area, the flood extent and volume
increase with the increased in return period.
7/27/2019 Full Report2
4/15
Figure 1.3: Location liable to flooding at a return period of 1 in 50, 100 and 200 years with no flood defences
7/27/2019 Full Report2
5/15
2. Flood Defence Measures: Flood protection level is set to 100yrs return period at Upton
upon Severn town.
Simulation of Existing River Section (ISIS 1D)-Increase conveyance capacity
Purpose: To obtain design flood hydrographs for the rivers
To obtain design flood levels along the river system
To determine the flood protection levels at various stretches of rivers
Water level profile of 100yrs return period for long section of River Severn
Water level profile of various ARI (50, 100, 200) at cross section M37
7/27/2019 Full Report2
6/15
Simulation of Floodplain (ISIS 2D)-control flooding
7/27/2019 Full Report2
7/15
7/27/2019 Full Report2
8/15
PossibleOptions
Advantages Disadvantages
Gazetting thelow-lying areasas floodplain
corridor andonly controldevelopment ispermissible
Urbanisation is inevitable
Development pressure
Floodforecasting andwarningsystems: toprovidesufficient leadtimes forrelevant
authorities toevacuatepotential floodvictims to safeareas.
Minimise flood damage Proper planning and failure of itcan cause severe damage andflooding
From the possible options with advantages and disadvantages, in order to increase
conveyance capacity approaches for waterfronts, buildings floodwalls in the cities destroy
the citys window on the river. In this manner, it is possible to employ earth bund
1) Floodplain: construction of earth bunds at right bank to act as flood storage or build
storage at upstream for higher ARI when the existing or proposed river channels areinsufficient to cater the peak discharge (at source control)
Construct earth bunds at both banks with slope protection. Proposed earth bund (at both
sides of river back) along the lower reaches of the River Severn extending from M13 to M25
and M35 to M38 to provide 100yrs flood protection for present settlements.
3. The principles, assumption and uncertainties of error
The area is modelled using integrated 1D and 2D hydrodynamic model. By using iterative
procedures, it can be used to solve equations that are impossible to solve by normal
mathematical manipulation. It involves some element of simplification. 1D model is used for
in-bank modelling for predicting the conveyance capacity. Meanwhile, 2D modelling is used
to model the behaviour of flow movement in the floodplain (out-bank). 1D model solves St
Vernant and energy equations. The 2D model used shallow water solver for flows in
floodplain environments. ISIS 2D use the numerical schemes, ADI (Alternating Direction
Implicit), that are specifically developed to tackle for subcritical flows.
Assumptions:
Shear or turbulence and secondary currents are negligible (1D)- Resistance is
constant with time
Neglect turbulence/3D flow affects (2D)-Resistance is constant with time Mannings dependant for frictional resistance to flow (1D and 2D)
7/27/2019 Full Report2
9/15
Data quality from farmer A, Farmer B and Willow are acceptable.
Flood hydrograph for different return period have same shape and time to peak with
the 2000 flood hydrograph
Uncertainties
Error in data input
o Data (Flow, channel geometry)
o Coefficient (Roughness, discharge)
Effect of Vegetation, seasonal effects (Summer and winter)-roughness value
Topography data resolution (not capture important information such as river
crossings, height, etc.)
Grid size of flood extent
How could be reduced
Site investigation (verification process) Calibration and verification (Calibrate by comparing model output with observed data)
Land use map (In hydrodynamic modeling, land cover maps are commonly used to
parameterize floodplain roughness by assigning a roughness coefficient to each land
cover type (Chow, 1959).
Use high resolution data
Graph 2.1: Flood hydrograph for different return period
A discussion which considers the best modelling approach or type to use for this site.
Is the model you have used the most appropriate for this area or would yourecommend changes to the modelling approach? You should give convincing
7/27/2019 Full Report2
10/15
scientific/engineering reasons for your recommendations and discuss the
implications in term of data requirements.
For this site, the best modelling approach is 3D modelling since the study involved flood
investigation and need to investigate the conveyance capacity (1D) and the behaviour of
flow movement in the floodplain (2D). The model in this study is appropriate. There is nodifferent between the water levels on the floodplain from the 2D model with water levels in
the channel from the 1D model. and but in order to build the storage, the actual volume
need to take into account and if flood forecasting system need to be installed
The figure XX shows user that the time step is too small or too big for the simulation, also it
can implicate that the model is diverging. Poor Model Convergence: the values of model
convergence and iterations are not between tolerant boundaries. The model is not stable.
identify reasons for discrepancies based on what you have learnt about modelling
uncertainties.
7/27/2019 Full Report2
11/15
Uncertainty regarding roughness value for floodplain modelling
Design flood hydrographs input into hydraulic modeling in order to evaluate the capacity
and conveyance of the rivers;
Finally, design discharge information for the river systems are used to develop and test
various flood mitigation option.
Channel and floodplain roughness is 0.07 (global roughness value for the entire area rather
than spatially varying roughness)
Flood Mitigation Engineer has to estimate the flood discharge and volume to size a
flood storage pond and to determine channel capacity.
Spatial resolution
Grid size
Decrease time step
Flood protection level should be 100-year ARI
7/27/2019 Full Report2
12/15
PMF
May need to wait for a flood to calibrate models correctly
Design Flood Hydrograph will be used the flow in autumn 2000 flood event by scaling the
flow using flow multiplier. In the real case time to peak and flood volume may differ.
It is used to measure the 'characteristics' of a river eg the gradient, the velocity etc. The
flood hydrograph is basically a dual plot of river discharge (line) and rainfall (bars) over
time.A large range of factors control the shape of hydrographs. These include: precipitation
type and intensity, catchment shape, catchment gradient, land use and vegetation (eg
afforestation, urbanisation), soil type, geology etc
Basic Data
Parameters
Boundary Data-upstream and downstream conditions
Calibration and verification data
The digital elevation model (DEM) used in the model is from LiDAR
River and reservoir routing may need inputs from groundwater, irrigation canal diversions (if
ada), public and industrial water supply
Inadequate
Bridge?
7/27/2019 Full Report2
13/15
Based on flow data from 1970-2009, Probable Maximum Flood, which is the estimation of
the greatest flood that could occur at Upton-upon Severn is 1200 m3/s. This PMF might be
appropriate if the dam are built on a river upstream or protection of nuclear plant or chemical
works.
Hydrological analysis is concern with
The estimation of magnitude of flood discharge, flood volume, rainfall intensity
The stage discharge relationship were established using the observed flood gauge and
discharge data
The best modelling approach
Type of Data Purpose (Type of Analysis)a) Hydrological Data- Rainfall- Streamflow / Discharge- River stage- Hydrology analysis, IDF curve, hydrological modelling andhydraulic modelling.- Hydrology analysis (hydrograph), rating curve, hydrologicalmodelling and hydraulic modelling.- Hydraulic analysis, rating curve, flood map and hydraulicmodelling.b) Hydraulic Data
- Sediment data- Tidal data- Hydraulic analysis and hydraulic modelling.- Hydraulic analysis and hydraulic modelling.c) River Characteristics- Cross-section and Longitudinal Section- River Geometry- River Structure- Hydraulic analysis, hydraulic modelling and detailed design.- Hydraulic modelling.- Hydraulic analysis, flood map, detailed design and hydraulicmodel.d) Maps & Plans- Topographic maps- Structural plan & drainage layout
- Local development plan- Master development plan- Landuse map (existing & future)- Soil map- Geology map- Contour map- Site survey plan- Cadastral plan/ Sheet- Hydrology analysis, hydraulic analysis and flood map.- Hydraulic analysis and flood map.- Hydraulic analysis, flood map and detailed design.- Flood map, detailed design and hydraulic analysis.- Hydrology analysis, hydraulic analysis, flood map andhydrological modelling.- Hydrology analysis, sedimentation and erosion analysis.- Detailed design.- Flood map and hydraulic modelling, hydrology analysis- Hydraulic analysis, flood map, hydraulic modelling and detailed
7/27/2019 Full Report2
14/15
design.- Hydraulic analysis and flood map, detail designe) River Section & Corridor Survey- River section- Corridor survey- Hydraulic analysis and hydraulic modelling.- Hydraulic analysis and flood map.
f) Satellites & Images- Images (Aerial photograph)- Digital Earth Model (DEM) & DigitalTerrain Model (DTM)- Satellite imagery (Earth Mapping)- Flood map.- Hydraulic analysis and flood map.- Flood map.g) Vulnerability Data- Socio-economy data- Physical Data- Flood damage assessment and ERP.- Flood damage assessment.h) Data for Previous Flood Events & RelatedStudies- Flood prone area
- Flood level- Extend of flooding- Flood depth- Flood damage- Flood history- Documented report- Oral/communication/interview- Built-up platform level and flood map.- Hydraulic analysis, flood map and hydraulic modelling.- Hydraulic analysis and flood map.- Hydraulic analysis and flood map.- Hydraulic analysis and flood map.- Hydraulic analysis and flood map.- Hydrology analysis, hydraulic analysis, flood map, flood damageassessment and detailed design.
- Hydrology analysis, hydraulic analysis, flood map, ERP and flooddamage assessment.i) Flood Properties - Flood risk and detailed design.j) Soil Investigation - Detailed design.k) Catchments Characteristics - Hydrology analysis, hydraulic analysis, hydrological modelling andhydraulic modelling.l) Data for Operation and Maintenance - As Built Plan- Standard Operation and Maintenance Procedure
An explanation of how the flood risk of the area is likely to change with time, and
make recommendations for any actions the local authorities (EA, local council, water
company, fire service, etc) can make.
A stream periodically changes by flowing over its banks.
Climate change may alter the flow characteristics. Pgv26 floodplain mgt
7/27/2019 Full Report2
15/15
References
Natural Resources Conservation Service, 2001. Stream corridor restoration.
http://www.nrcs.usda.gov/wps/portal/nrcs/detail/national/ndcsmc/?cid=nrcs143_009158
Recommended