Lecture 10 Flashcards
flood maps are used to
identify areas that could be affected by floods (floodplains)
what are some types of floodplain maps
flood hazard maps
flood risk maps
flood hazard maps identify
areas that would be effected by events of different return periods
flood risk maps identify
vulnerable infrastructure and the potential consequences associated with specific flood events.
In nova scotia flood mapping studies have focused on
identifying the 1:00 and 1:20 year floodlines
the 1:20 year floodline is known as the
Floodway. This is the area that is more frequently
flooded, conveys the majority of floodwaters, and
would have the greatest water depths and velocities
* Different land use restrictions would be applied to the
1:20 and 1:100 yr floodlines
Elements of a Floodplain Delineation Study
Hydrology
* Predicted peak flows
* Frequency Analysis
* Hydrological
Modeling
Hydraulics
* Computed
water surface
profile at peak
flows
* Steady vs
Unsteady State
Mapping
* Floodplain
extents
* Hazard Zones
* Risk Zones
Elements of a Floodplain Delineation Study: hydrology
- Predicted peak flows
- Frequency Analysis
- Hydrological
Modeling
Elements of a Floodplain Delineation Study: hydraulics
- Computed
water surface
profile at peak
flows - Steady vs
Unsteady State
Elements of a Floodplain Delineation Study: mapping
- Floodplain
extents - Hazard Zones
- Risk Zones
Additional factors that cause flooding
- Ice jams
- Hydraulic structures
– Culverts (blockages)
– Bridges - Confluence of rivers
- Tidal boundary
conditions
Case Study: Sackville and Little Sackville Rivers
information
- 150 km2 vs 15 km2
- Primarily rural
(Sackville) vs highly
urbanized (Little
Sackville) - Downstream
boundary condition
(Bedford Basin)
Developed maps of
* 1:20, 1:100. 1:500 and Probable Maximum
Precipitation floods
* Historical and future climate rainfall and sea level
rise
* Hydrologic model: PCSWMM
* Hydraulic model: PCSWMM and HEC RAS
Water Survey of
Canada
* Sackville River
* Little Sackville
River
* ECCC climate
stations (3)
* Dalhousie Centre for
Water Resources
Studies
* 6 additional
water level
monitoring
stations
Snowmelt Contributions
- Depth
- Density
- Snowwater
Equivalent (SWE) - Ablation
Empirical Snowmelt
Models
Empirical snowmelt models
take the form of TemperatureIndex Equations:
Δw = M (Ta – Tm) when Ta ≥ Tm
Δw = 0 when Ta < Tm
Types of Hydrological Models
- Temporal Basis
* Steady vs Unsteady State
* Event vs Continuous - Spatial Basis
* Lumped
*Distributed
* 1, 2, or 3 Dimensional
Continuous Models
Simulate both “Wet” and “Dry” hydrologic processes
Wet Processes
*Precipitation type
* Infiltration
* Runoff
Dry Processes
- Evapotranspiration
- Soil water redistribution
- Baseflow (interflow and shallow groundwater flow)
lumped spatial model
rainfall properties arranged over basin
one rainfall/runoff model
prediction at only one point
distributed spatial model
rainfall properties in each grid
rainfall/runoff model in each grid
prediction at many points
Semi-Distributed Models
- Watershed is classified into units of land that have similar
hydrologic characteristics (Hydrologic Response Units
(HRUs)) - The Soil and Water Assessment Tool (SWAT) is a SemiDistributed Model
Some Things to Consider When Designing or
Selecting a Hydrologic Model
- What is the purpose of the model?
- What scale is required?
- What input data is required?
- How will I calibrate and validate the model?
- What are the software/hardware requirements to run simulations?
Need to consider the catchment and conditions you are trying to model!
The components of a hydrologic model
depends on the catchment and characteristics you are trying to model
Example Model Structure: HEC-HMS
Event and continuous model developed by US
Army Corps of Engineers
Example Model Structure: HBV
Continuous hydrologic
model developed by
Swedish Meteorological
and Hydrological Institute
(SMHI)
for each hydrologic response unit (HRU)
Layer 1 and 2
(snow and melt water)
Layer 3 (soil)
Layer 4 (upper
groundwater)
Layer 5 (lower
groundwater)
Many model input parameters cannot be estimated by actual
measurements therefore
, in general, a model will have to be
calibrated
Even if a parameter is measured
it is typically not at a scale that is
compatible with the modeling scenario
what is calibration
varying values of input parameters (optimization) so that
model outputs match measured data (model can be run dozens or
hundreds of times to get an acceptable match) – goodness of fit tests
what is Model Validation
Testing calibrated model with an independent set of observed
data that are different from those used in the calibration
two kinds of model validation
Temporal Validation (Split Sample)
* Spatial Validation (Nested Watershed, Paired Watershed)
what ways can goodness of fit or model performance be assessed
- Graphical
- Statistics
- Water Balance Assessment
Widely Used Hydrological Models
HEC-HMS - Event model that simulates hydrology. Developed and
supported by the US Army Corps of Engineers
* SWMM – Storm Water Management Model. Event model which simulates
hydrology and water quality in urban areas. Developed and supported by
USEPA (Commercial versions include PCSWMM and XPSWMM)
* TR-55 – Event model that simulates hydrology. Developed and supported
by US Natural Resources Conservation Service (NRCS)
* HSPF – Hydrologic Simulation Program-Fortran. Continuous watershed
model that simulates hydrology and water quality. Supported by the
United States Environmental Protection Agency (USEPA)
* SWAT – Soil and Water Assessment Tool. Continuous watershed model that
simulates hydrology and water quality. Supported by the USEPA and US
Dept of Agricultur
- HEC-HMS -
Event model that simulates hydrology. Developed and
supported by the US Army Corps of Engineers
- SWMM –
Storm Water Management Model. Event model which simulates
hydrology and water quality in urban areas. Developed and supported by
USEPA (Commercial versions include PCSWMM and XPSWMM)
TR-55 –
Event model that simulates hydrology. Developed and supported
by US Natural Resources Conservation Service (NRCS)
- HSPF –
Hydrologic Simulation Program-Fortran. Continuous watershed
model that simulates hydrology and water quality. Supported by the
United States Environmental Protection Agency (USEPA)
SWAT –
Soil and Water Assessment Tool. Continuous watershed model that
simulates hydrology and water quality. Supported by the USEPA and US
Dept of Agriculture
Baker lake case study info
Using HEC-HMS to Simulate the
Hydrology of a Arctic Watershed Impacted by
Wastewater Effluent
Water quality monitoring (Jun
2018
– Sept 2019)
* Continuous flow measurements
(Jun 2018
– Sept 2019)
* Surveying bankfull channel
geometry (Sept 2019)
* Bathymetry studies (Sept 2019
Hydrological Transport
Model * Frequency analysis:
2, 10, 25, & 100
-year return
periods
* Wetland Contaminant Fate
and Transport Model
LID on groundwater case study info
Using PCSWMM to Assess
Effects of Low Impact Development on
Groundwater Availability
In this case study LID implementation was predicted to have
modest positive impacts on groundwater levels
* However, the proposed development (without LID) was
predicted to have only minor impacts on groundwater levels
* LID effects would be more pronounced in different
hydrogeologic environments or development scenarios
what is PCSWMM
- Commercial version of the
EPA SWMM model - Urban hydrology and
hydraulics - Event and Continuous
modeling capabilities - Explicit simulation of Low
Impact Development (LID)
systems - Rain Gardens (Bioretention
Systems) included on all
residential lots
