Hydrology Flashcards
Synder method
Convert observed storm unit hydrograph for a similar catchment
Synder method steps
- Measure storm length, time of peak flow, and peak flow
- Calculate Cp and Ct for UH
- Decide time for new storm then calculate parameters
Limitations of synthetic unit hydrograph
- Empirical method: equations derived from prior analysis of data not physics of flowing water
- Event centric: rainfall/runoff considered in isolation from other catchment conditions
Control volumes of water storage examples
Snowpack, lakes, groundwater
Nash reservoir
Linear reservoirs output becomes input to another reservoir in series
Evapotranspiration
Combination of evaporation and plant transpiration
Evaporation
Liquid water to water vapour
Plant transpiration
Vaporisation of liquid water contained in plants
Potential ET
Accounts for evaporation from water bodies or bare soil (Penman)
Reference ET
Accounts for two vegetation types (Penman-Monteith)
Infiltration
Subsurface flow of water from ground surface into soil
What causes infiltration?
Weight of water and capillary suction fuel infiltration, initially rapid then slow
What does a high clay percentage mean for infiltration?
High suction head and lower conductivity
Green & Ampt method objective
Given a rainfall hyetograph, calculate infiltration and runoff
Green & Ampt steps
- Calculate soil parameters
- Calculate rate of infiltration
- If rain, i, less than f all infiltrates, greater than f, only a fraction infiltrates
- Calculate infiltration update
Phi-index
Infiltration rate calculated from the difference between observed rainfall and streamflow
Horton
Infiltration is assumed to be an exponentially decaying curve, take measurements to determine parameters
Overland flow
During storm events, rain travels over the ground, first in sheets, then in small rills, eventually concentrating in larger gullies and channels
Time of concentration
Travel time of longest catchment distance
Kinematic wave equation
Describes transport of water: overland as runoff, in a channel, or a stream
Solved using finite differences approximation
Muskingum parameter K
Time for flood wave to travel the x distance
Muskingum parameter X
Parameter that controls the amount of diffusion
Recurrence relation for muskinum method
2KX < t < K
Muskingum Cunge method
Approximates wave diffusion using channel properties by discretizing the kinematic wave equation on the x-t plane
Numerical stability for Muskingum Cunge method
0 < X < 0.5
Selection of parameter X for Muskingum-Cunge method
Calculated as a function of physical properties: length, discharge, width, celerity and channel bottom slope
Storage-Indication Method
Method for determining outflow and storage for a linear reservoir
Storage-Indication method steps:
- Determine storage and outflow as a function of height
- Complete storage-indication calculate
- Interpolate between table values using rainfall intensity
- Present updated outflow and storage
