Mention the objectives of rainfall-Runoff modelling
- Assessment of design of floods for planning dams, flood control reservoirs, urban drainage networks, bridges, etc.
- Real Time forecast of floods (flood warnings and control of reservoirs)
- Impact analysis (effects of land use change, climate change on flood flows and flood protection measures)
Phases of rainfall Runoff transformation:
- Runoff generation
- >Prediction - Runoff transformation (concentration)
- > Prediction - Flood routing (Discharge process)
Classification of models according to target variables
- Rainfall-Runoff-Models (RR-Model) -> Floods (Q)
- Water balance models -> (ETR, Q, Rx)
- Ecohydrological models -> Nutrients (N,P,…)
- Groundwater models -> Groundwater flow, mass transport
Clasification of models according to purpose:
- Forecast: Real time forecast, operation model (floods)
- Prognosis (simulation): planning, design, impacts
- Research: Formalistion and test of research hypotheses
Methods to calculate the runoff generation:
- Runoff cofficient, Φ-Index ->Simple abstraction methods
- Horton -> Empirical time dependent functions
- Richard’s eq., Green Ampt, etc -> Physically based infiltration and soil water balance models.
Which are the 2 most important parameter functions for the infiltration process characterizing soil properties?
Hydraulic conductivity k
Suction head ψ
Mentimeter:
How can you assure linearity and time invariance when applying the unit hydrograph?
- Separate the base flow from the hydrograph
- Apply a runoff generation method beforehand.
Methods to calculate the runoff concentration:
- System hydrological methods (unit hydrograph, pulse response function)
- Conceptual models (linear reservoir, Clark-Model, time-area method, etc)
- Physically based models (3D Richard’s eq., groundwater models)
Assumptions when applying a system hydrologic concepts (e.g. unit hydrograph):
- Proportionality
- Superposition principle
- Time invariance
What is the Unit Hydrograph?
The UH is the direct runoff hydrograph of a watershed
resulting from 1 mm effective rainfall occurring uniformly over the drainage area at a constant rate for a specific duration.
Methods for flood routing:
Hydrological methods: -Muskingum -Kalinin-Miljukov
Hydraulic methods: -Saint-Venant -Translation-Diffusion -Kinematic wave
Standart functions of system hydrology:
- Unit step input ε(t) -> Step response function h(t)
- Unit pulse input u(t) -> Pulse response function g(Δt,t)
- Unit impuls input δ(t) -> Impulse response function g(t)
