Chapter 5. Rainfall Runoff Modelling

Question 1

Mention the objectives of rainfall-Runoff modelling

Answer 1

1. Assessment of design of floods for planning dams, flood control reservoirs, urban drainage networks, bridges, etc.
2. Real Time forecast of floods (flood warnings and control of reservoirs)
3. Impact analysis (effects of land use change, climate change on flood flows and flood protection measures)

Question 2

Phases of rainfall Runoff transformation:

Answer 2

1. Runoff generation
   - >Prediction
2. Runoff transformation (concentration)
   - > Prediction
3. Flood routing (Discharge process)

Question 3

Classification of models according to target variables

Answer 3

• Rainfall-Runoff-Models (RR-Model) -> Floods (Q)
• Water balance models -> (ETR, Q, Rx)
• Ecohydrological models -> Nutrients (N,P,…)
• Groundwater models -> Groundwater flow, mass transport

Question 4

Clasification of models according to purpose:

Answer 4

• Forecast: Real time forecast, operation model (floods)
• Prognosis (simulation): planning, design, impacts
• Research: Formalistion and test of research hypotheses

Question 5

Methods to calculate the runoff generation:

Answer 5

• 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.

Question 6

Which are the 2 most important parameter functions for the infiltration process characterizing soil properties?

Answer 6

Hydraulic conductivity k

Suction head ψ

Question 7

Mentimeter:

How can you assure linearity and time invariance when applying the unit hydrograph?

Answer 7

• Separate the base flow from the hydrograph

- Apply a runoff generation method beforehand.

Question 8

Methods to calculate the runoff concentration:

Answer 8

1. System hydrological methods (unit hydrograph, pulse response function)
2. Conceptual models (linear reservoir, Clark-Model, time-area method, etc)
3. Physically based models (3D Richard’s eq., groundwater models)

Question 9

Assumptions when applying a system hydrologic concepts (e.g. unit hydrograph):

Answer 9

1. Proportionality
2. Superposition principle
3. Time invariance

Question 10

What is the Unit Hydrograph?

Answer 10

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.

Question 11

Methods for flood routing:

Answer 11

Hydrological methods: -Muskingum -Kalinin-Miljukov

Hydraulic methods: -Saint-Venant -Translation-Diffusion -Kinematic wave

Question 12

Standart functions of system hydrology:

Answer 12

1. Unit step input ε(t) -> Step response function h(t)
2. Unit pulse input u(t) -> Pulse response function g(Δt,t)
3. Unit impuls input δ(t) -> Impulse response function g(t)