Flood Risk Assessment: Flood Hydrograph Simulation - Conceptual Model Flashcards
What are the 3 types of Hydrological Models?
- Empirical (Black Box)
- Conceptual
- Physically - based
What is the definition for an empirical model?
Uses input-output relationships from data, no process simulation
Definition for conceptual model?
Simplified process representation using stores and rules
Definition for physically-based model?
Solves physical laws via numerical methods
What are limitations of the unit hydrograph method?
- Ignores evapotranspiration and baseflow
- Assumes time-invariance
- Doesn’t simulate full streamflow time series
Conceptual models use series of _______ with parameters to control flow and losses.
stores
Components within the water system?
- Water demand
- Water resources
- Water networks
What are elements within the water demand?
Population, irrigation, indoor use
What are elements within the water resources?
Precipitation, groundwater, surface water
What are elements within the water networks?
Supply, leakage, wastewater, stormwater discharge
What is field capacity?
Max soil moisture held without drainage.
What is the wilting point?
Soil moisture level below which plants wilt.
What is Soil Moisture Deficit (SMD)?
Air content in the soil.
What is infiltration excess?
When rainfall exceeds the soil’s infiltration capacity.
What is saturation excess?
When soil is already fully saturated (SMD = 0).
What is NEAR (Non-Effective Area Runoff)?
Runoff from impervious surfaces that flows into pervious areas.
What is the run off behaviour like in a pervious area?
Overland flow via infiltration/saturation excess
What is the run off behaviour like in a impervious area?
Divided into NEAR and EAR
Impervious Area Calculations
Formula
Evapotranspiration
PET = Ke × ET₀
AET = min(PET, IL, P)
- Ke = evaporation coefficient (0.1 for bare soil)
- IL = initial losses (mm)
- P = precipitation (mm)
Formula
Surface Runoff
EAR = EA × max(P − AET, 0)
NEAR = (1 − EA) × max(P − AET, 0)- EA = % of area hydraulically connected to storm sewer
Soil Moisture Calculation (Pervious Areas)
Formula:
PSMD(i) = SMD(i − 1) + PE(i) + R(i) − P(i) − NEAR(i)
Where:
SMD = Soil Moisture Deficit
PE = Potential Evaporation
AE = Actual Evaporation
R = Recharge
P = Precipitation
NEAR = Non-effective runoff
When is AE(i) limited to WP − SMD(i−1)?
When PSMD(i) > WP
True/False
If PSMD(i) < 0, excess precipitation becomes effective rainfall.
True
What’s the first step before calculating streamflow using a routing model?
Estimate total runoff (EAR + NEAR), then apply routing equations.
