Hydrological equations generally refers to water balance at the basin scale expressing the equality between an inflow and an outflow at the hydrological year time step.
The general equation for the water balance performed in each Irrigation District (ID) is:
I + P + OIn – (Q + ETc +OOut) = ΔW
where I is the volume of water diverted for irrigation from outside the ID; P is the precipitation; and OIn stands for other inputs, specific to each basin. The outputs considered are the surface outflow from the district (Q, except for the Beni Amir ID where the outflow is underground), the evapotranspiration of the crops (ETc); and other outputs, also specific to each basin. The difference between inputs and outputs along a given period (like a hydrologic year) must be equal to the change in soil and aquifer water storage in the ID (ΔW) and thus the closing error of the balance is given by Inputs – Outputs - ΔW.
The hydrological equation are different in formulas and it's own implication. The method and the tools that u apply may differ for all equation and it's out put so to apply the equation ur objective and expected output matter.
Yes, there are various hydrologic equations (plural) employed in water studies according to various applications as well as various purposes.
Simplest one should be Total in - Total out = Storage whereas
Total in: total inputs into your given watershed (rainfall, snow melt, ..)
Total out: outflows + losses (infiltration, evaporation,...)
Storage: the leftovers or water availability at a given time step
There is not only one "hydrological equation" to refer to. The water balance equation for example expresses a key principle in hydrology. Other equations may refer to hydrological processes like evapotranspiration, infiltration, groundwater pumping etc.
Hydrological equations are not one general equation. They depend on the objectives of hydrological study.
In hydrologic terms, the water inventory equation (Inflow = Outflow + Change in Storage) which expresses the basic principle that during a given time interval the total inflow to an area must equal the total outflow plus the net change in storage
The horological equations is mainly the mass balance equation. Which means what flow enter the catchment such as rainfall water from rivers and seepage from groundwater and what flow is out from the catchment such as outflow discharge evapo- transpiration. percolation to ground water
Hydrology is a broad scientific field where old-folks wisdom, receipes, most recent advances in observation technologies (satellites ..) and data transmission up to big-data processing techniques meet each other to serve the people. I agree with my colleagues that there is no single "super" equation which may serve as a fundament. The rules of groundwater hydrology ("Darcy") and the water-balance equation surely are major parts of the business, but in cases also basic equations of hydraulics (St. Venant) and even hydrodynamics (Navier-Stokes) with their rules for flow resistance, mixing of water masses etc. are on board. However, also demographic aspects and socio-economy may play big roles: A broad field of extreme importance for the future of mankind.
The general conservation equations for mass, momentum, and energy for the case of flowing fluids (as applicable in Hydrology) - the following article may be referred.
Beckie, R. 2006. Fundamental Hydrologic Equations. Encyclopedia of Hydrological Sciences. 1:5.
I recommend that you download and read this book on the equations that dominate the hydrology, hydrology pra a better understanding is divided into two: surface hydrology studying relation to the hydrological cycle and surface water and groundwater hydrology studies the underground water this book will give you ideas about this.
geog.ucsb.edu/.../L6_Hydrologic_processes.pdf
geog.uvic.ca/.../370_3_waterbal_Spring_13.pdf
For Hydrological equation please refer :
Classical books like Garrels and Thomsion,
Garrels and Crist
The hydrologic equation is simply the statement of the law of conservation of matter and is given by : Inflow = Outflow + Change in Storage
The hydrological basic equation describes the hydrological cycle in a quantitative way:
P = R + E
P = Precipitation; from aerosphere retiraled water
E = Evaporation from soil and free expanses of water
R = Run-off
The water balance for lakes can be expressed as:
∆ S = P – ET – R – r
where
P is the precipitation,
E is the s evapotranspiration,
R is the surface runoff into lake, and
r is the recharge.
I strongly recommend you to also calculate the runoff coefficient which is R / P (%)
Its variablity is linked to the changes in climate and land use, and its study helps in understanding what are the main drivers of the runoff variability, either climatic or anthropogenic.
You can find a study where it is used in the attached doc.
Best
Gil
In addition to the answers of our colleagues two points:
- The use of a particular (set of) equation(s) indeed depends on the purpose of the study, but also on the data availability, hydrological characteristics and variability of the study area, spatial and temporal scales and required accuracy of the results. Complex equations for instance for surface runoff might be inappropriate when data availability is scarce and parameters in equations can not be properly estimated. On the other hand, for small spatial and temporal scales changes in water storage can not be neglected and the equation P (precipitation) = ET (evapotranspiration) + Q (discharge) does not hold anymore.
- Besides the water balance also the energy balance is important for hydrology, in particular when ET is important (in many situations) and changes in e.g. land use affect ET and the hydrological cycle.
Regards,
Martijn
I saw this question early on, and decided how could I answer. There are some key equations we may use as hydrologists, but doubtful we can name them all. There are model equations that hydrologists have developed to address specific circumstances through time. In the earliest of times, philosophers postulated about the movement of water and how to make it work for us. The equations encompass many interactions with the laws of gravity, chemistry, physics, and our environment including air, soil, geology, volcanoes, streams and water convenances, etc. Man has done many things in his attempts to control water, store water, relocate it, etc. I would say that all life depends on water, but sure enough, someone would prove me wrong, just as if I put up a list of hydrologist equations, I would not have them all. But as hydrologists there are many responses coming from our desire to help others understand both the basic simplicities, but also the complexities in understanding water, how it moves through the systems of life and this planet, perhaps even solar system, galaxy. The hydrologists I know are resilient, problem solvers, and if they do not have a suitable equation to help solve a problem, they will collect enough information or use their expertise to find a suitable solution. Occasionally for expediency, we have to give an educated guess. I know that even though I don't know that magic hydrology equation, I have learned enough from others, in reading and studying through my career that I will never know it all. But there is something engrained in us hydrologists, perhaps the challenge of that problem. We are up for the challenge to develop an answer. As a practicing hydrologist, I often rely on observing and reading the ground and streams, erosion, aquatic indicators and knowing where to find appropriate data if I need some collaboration, more than I do relying on equations or massive data collections. That magic equation may not be a formula after all, but must be set in our hydrologist mind and determination to get the job done right. There are also no limit to the technical skills we might have to consider and apply including lawyer, botanist, soil scientist, aquatic biologist, engineer, archeologist, ecologist, meteorologist, inventor, ditch digger, geologist, philosopher, GIS, etc.
- Badges
- Science topic
- Similar topics
- Geoscience
- Hydrology