1. Hydrology and Hydrogeology
Dr. Shimelis G Setegn, Ph.D.
Program Executive Officer- GLOWS
Research Assistant Professor - RSCPHSW

2. HYDROLOGY
Hydrology is the science that deals with the occurrence, circulation and distribution of water upon, over and beneath the earth surface.
It is the science concerned with the transportation of water vapours through the air, the precipitation occurring on the ground as rainfall and the flow of water over the ground surface and through the underground strata of the earth.

3. HYDROLOGY
It also deals with the evaporation from water surface and soil surface, the infiltration through the ground surface and the transpiration from the plants and various other allied processes occurring in nature.

4. Importance of Hydrology
A basic knowledge of hydrology is essential for the irrigation engineer engaged in the development, utilization and management of water resources
It helps assessing the quantity of water available for irrigation, hydropower, municipal and industrial water supply and other purposes.
It is required for the estimation of the maximum discharge for the design of spillways, aqueducts, bridges, and sewers.

5. Hydrological studies are also necessary for flood control, erosion control, pollution control, etc.
Hydrology is basically an applied science. the subject is sometimes classified as
Scientific Hydrology: The study which is concerned mainly with academic aspects.
Engineering or applied Hydrology: a study concerned with engineering applications.

6. In general, engineering hydrology deals with
Estimation of water resources.
The study of processes such as precipitation, runoff, evapotranspiration and their Interaction
The study of problems such as floods and droughts and strategies to combat them.
which enable a quantitative evaluation of the hydrologic processes that are of importance to a civil, agricultural or soil & water eng.

7. Sources of data
Depending upon the problem at hand, a hydrologist would require data relating to the various relevant phases. The data normally required are:
Weather records:- temperature, humidity, and wind velocity,
Precipitation data,
Stream-flow records.
Infiltration and transpiration data,
Evaporation characteristics of the area,
Ground water characteristics
Physical and geological characteristics of the area under consideration

8. Sources:
Meteorological data are collected from Meteorological service agency.
Stream flow data of various rivers and streams can be found from Ministry of water resources.
Data on Evaporation, transpiration, infiltration will be available in ministry of agriculture, or water resources or any other concerned departments.
The physical data of the area can be obtained from topographic map of the area available with mapping agencies.

9. The Hydrologic cycle:
- The main components of the hydrological cycle are rainfall (precipitation), evaporation, Transpiration, Infiltration, runoff and ground water.
beginning with the evaporation of water from the ocean.
The resulting vapour is transported by moving air masses.

10. The Hydrologic cycle:
Under the proper condition, the vapour is condensed to form clouds, which in turn may result in precipitation.
The precipitation which falls up on land is dispersed in several ways.

11. The Hydrologic cycle: continued
The greater part is temporarily retained in the soil and is ultimately returned to the atmosphere by evaporation and transpiration
a portion of the water finds its way over and through the surface soil to stream channels, while other water penetrates farther into the ground to become part of the ground water.

12. Phases of hydrologic cycle simulated by SWAT
Land
phase
Water phase
• First, set up the physical setting of the watershed -- its topography, soils, land cover (comprises vegetation, land use, management practices, and the like)
• Then, input climatic variables, such as precipitation, solar radiation, temperatures, wind speeds, relative humidity, etc.
• The model simulates the watershed hydrological processes -- how much of the precipitation is intercepted, how much infiltrates, how much runs off, how much transpires, and so forth.
• The model can also calculate some water-quality variables, i.e., how sediment and nutrients (and some pesticides) move through the system and are modified.
• Finally, the model outputs the volume and rate of outflow of water at the bottom of the watershed, along with the loading of selected water-quality variables
• HYDROLOGY IS THE MAIN DRIVER HERE!! The model figures out how water moves through the system first, and then calculates how sediment and nutrients are carried along by that water.
Courtesy:
SWAT Manual

13. Under the influence of gravity, both surface stream flow and ground water move toward lower elevations and may eventually discharge into the ocean.
How ever, substantial quantities of surface and under ground water are returned to the atmosphere by evaporation and transpiration before reaching the ocean.

14. Groundwater Hydrology

15. Ground water
Ground water is the most important source of fresh water today, not surface waters (lakes and rivers).
Supplies 34 out of 100 largest U.S. cities because
1)    Precipitation varies dramatically, particularly in arid areas where little or no surface water exists.
2)    Surface water often polluted.
3)    Often it is naturally filtered
4)    Largest available source of fresh, liquid water.

16. What is groundwater?

17. Terms
Porosity - Ratio of Void Volume to Total Volume of Soil

18. Terms cont.
Permeability - A measure of the resistance to flow through a porous media.

19. What is saturation?
In the saturated zone all of the pore space is occupied by water
In the unsaturated or vadose zone, both air and water are found in the pore space

20. What are aquifers?

21. GW cont.-Aquifer
Large volumes of ground water require an aquifer that holds and transmits the water.
Material has a high porosity and permeability.
Usually a well-sorted sediment rock or sedimentary rock.
Flow rates of meters per day for sand and sandstone and per day for gravel or conglomerate are typical.
Aquiclude: impermeable to water flow. Acts as a barrier (i.e. shale).
Aquitard: intermediate condition

22. Aquifer Types
 Unconfined: no confining aquiclude on top of aquifer. Water is not under any pressure. Aquifer is open to surface waters (and pollution) throughout its entire area. Usually is regional in extent (100s of square miles or more).
 Perched water table: localized (10s of square miles or less) unconfined aquifer usually at a shallower depth than the regional aquifer. Caused by underlying aquiclude of limited extent. Cheaper to exploit, but can be quickly depleted and is more sensitive to local precipitation and pollution.
Confined of artesian: overlain by an aquitard or aquiclude. Water movement restricted to the sandwiched aquifer. Water usually under pressure due to its own weight (hydrostatic head). If drilled, water will rise to the potentiometric surface.

23. Aquifers types cont.
Unconfined Aquifers: When saturated conditions are found with impermeable material between the aquifer and ground surface, we term this an unconfined aquifer, water table aquifer, or a phreatic aquifer.
If a well is drilled into this aquifer, the water level in the well defines the water table, phreatic surface or the piezometric surface

24. Unconfined Aquifers
The piezometric surface move up and down depending on the amount of water in the aquifer
The addition of water to the aquifer is termed recharge
The elevation (above sea level) of the surface of the aquifer is termed the head
The change in head, or head loss, with distance is termed the hydraulic gradient
Groundwater flows down the hydraulic gradient

25. Hydraulic gradient in unconfined aquifers

26. Hydraulic Gradient where h1 = head at location 1
L = distance between locations 1 and 2

27. Confined aquifer
Aquifer which is between 2 impermeable layers (aquicludes) Can be "leaky" in which case the aqucludes are replaced by aquitards.
Equation for flow per unit width (Q') in a confined aquifer;
K = Permeability
D = Thickness of Aquifer
L = Distance between Head (H) Measurements
R = Distance from Well to H measurement

28. Unconfined aquifer Flowrate per unit width of the aquifer
K = Permeability
H1 and H2 = Head above confining layer
L = Distance between H measurements
R = Distance from Well to H measurement

29. Groundwater Flow Darcy’s Law
where v = groundwater “Darcy” velocity (m/d)
K = hydraulic conductivity (m/d)
where Q = flow rate (m3/d)

30. Hydraulic Conductivity

31. Example
A medium of sand aquifer 20.0 m thick has two monitoring wells spaced 500 m thick along the direction of flow. The groundwater level in the first well is m above sea level, and m in the second well. Estimate the rate of flow per meter of width (distance perpendicular to the flow).

32. Example

33. Average Linear Velocity
Darcy velocity is the flow per unit cross- sectional area of the aquifer
Much of the cross-sectional area is “blocked” by particles

34. Average Linear Velocity
Actual velocity of the water that moves through the pores is greater than the Darcy velocity
where v’water = average linear velocity (m/d)
v = Darcy velocity
η = poristy

35. Example
In the previous example, what is the average linear velocity of the water?

36. Hydraulic conductivity (K)
Hydraulic conductivity (K) of soil or rock depends on physical factors and is an indication of an aquifer’s ability to transmit water
Has a unit of L/T
Transmissivity (T)- a term applied to confined aquifers, T = K.b
B = aquifer thickness
T has the unit of L2/T

37. Intrinsic permeability (k)
It is the property of the medium only, independent of fluid properties. It is related to hydraulic conductivity
Where m = dynamic viscosity, r = fluid density and g = gravitational acceleration
K has units of m2
Intrinsic permeability (k) is used in petroleum industry and K is used in groundwater hydrology

38. Determination of Hydraulic conductivity (K)
Lab-
constant and
falling head permeameters
Field-
pump test,
slug test and
tracer tests

39. Determination of Hydraulic conductivity (K)
Permeameter is used to measure K by maintaining flow through a small column of material and measuring flow rate and head loss
For a constant head permeameter, Darcy’s Law can be directly applied to find K, where V is volume flowing in time t through a sample of area A, length L and with constant head, h

40. Determination of Hydraulic conductivity (K) cont.
The falling head permeameter, test consists of measuring the rate of fall of the water level in an attached tube or column and nothing that
Darcy law can be written for the sample as
Where r, rc are radii of the tube and sample respectively and t is the time interval for the water to fall from h1 to h2
After equating and integrating

41. Determination of Hydraulic conductivity (K) cont.
In the field, slug tests, pump tests and tracer tests are preferable for determination of K
They provide better estimate of field conditions
The slug test for shallow wells operates based on a measurement of decline or recovery of the water level, in the well through time.
The well can be pumped to lower the water level and allowed to recover in time or
Water level can be increased and allowed to drain out in time
Hydraulic K is then determined by evaluating the rate of change in the water level with time.

42. Determination of Hydraulic conductivity (K) cont.
The pump test involves the constant removal of water from a single well and observations of water level declines at several adjacent wells
Field test give usually yield different values of K than lab since they are accurate and indicate the field condition

43. Anisotropic aquifers
K can be different in the vertical and horizontal directions for most geologic systems
Mainly due to alluvial depositions
For two layered aquifer of different K in each layer and different thickness, we can apply Darcy’s law to horizontal flow to show
Or in general
Where Ki = K in layer i and Zi = thickness of layer i

44. Anisotropic aquifers cont
For vertical flow
Or in general
Where Ki = K in layer i and Zi = thickness of layer i

45. Urban watersheds and Hydrology

46. Volume
Peak
Time to peak
Tp ?
Qp ?
Flow
Volume ?
Time

47. Hydrologic Response vs. Land Surface Parameters and Fluxes
Surface energy fluxes
Fractional vegetation
cover
Impervious
Surface
Temperature
Topography
HYDROLOGIC RESPONSE
Land-cover
Snowmelt
Precipitation/
Soil moisture

48. Watersheds (a) (b) (c) Q time Original (natural) Partially developed
Fully
developed
(a)
(b)
(c)
(From: Hydrology and Floodplain Analysis, 2nd ed. P.B. Bedient and W.C. Huber, Addison-Wesley Pub. © 1992) Q
time

49. Land-use change effect on hydrology
Afforestation
Annual flow
Increased interception in wet periods
Increased transpiration in dry periods through increased water availability to deep root systems
Seasonal flow
Increase interception and transpiration will increase soil moisture deficit and reduce seasonal flow
Drainage activities associated with planting may increase dry season flow through initial dewatering
Cloud water (mist or fog) deposition will augment dry season flows

50. Land-use change effect on hydrology cont.
Afforestation
floods
interception reduces floods
Cultivation, drainage and road construction increase floods water availability to deep root systems
Water quality
Leaching of nutrients is less from forests through reduced surface runoff and reduced fertilizer applications
Deposition of atmospheric pollutants is higher

51. Land-use change effect on hydrology cont.
Afforestation
erosion
High infiltration rates in natural, mixed forests reduce surface runoff and erosion
Slope stability is enhanced by reduced soil pore water pressure and binding of forest roots
Wind throw of trees and weight of tree crop reduce slope stability
Soil erosion, through splash detachment, is increased from forests without an understory of shrubs or grass
Cultivation, drainage, felling and road construction increase erosion

52. Land-use change effect on hydrology cont.
Afforestation
Climate
Increased evaporation and reduced sensible heat fluxes from forests affect climate

53. Land-use change effect on hydrology cont.
Agricultural intensification
Water quantity
Alteration of transpiration rates affects runoff
Timing of storm runoff altered through land drainage
Water quality
Application of organic fertilizers
Application of persistent pesticides poses health risks to humans and animal life
Farm wastes pollutes surface and groundwater bodies
Erosion
Cultivation without proper soil conservation measures and uncontrolled grazing on steep slopes increase erosion

54. Land-use change effect on hydrology cont.
Draining wetlands
Seasonal flow
Upland peat bogs, groundwater fens have little effect in maintaining dry season flows
Wetlands loose their desired function (flood control, water quality improvement, recharge etc)

55. Reducing urban runoff: Parking Lots
Reducing runoff
porous pavement
Gravel parking lots
Porous or punctured asphalt
Concrete vaults and cisterns beneath parking lots in high value areas
Vegetated ponding areas around parking lots
Delaying runoff
Grassy strips on parking lots
Grassed waterways draining parking lot
Ponding and detention measures for impervious areas
Rippled pavement
Depressions
basins

56. Reducing urban runoff: Residential
Reducing runoff
cistern for individual or group of homes
Gravel driveways (porous)
Contoured landscape
Groundwater recharge
Perforated pipe
Gravel
Trench
Dry wells
Vegetated depressions
Delaying runoff
Reservoir or detention basin
Planting grass with high roughness value
Gravel driveways
Grassy channels
increased length of travel of runoff by means of gutters and diversions

57. Guidelines for Planning in an Urban Drainage Basin
Maximize the distance of storm water travel from the site to a collection area or stream.
Maximize the concentration time by slowing the rate of storm water runoff.
Minimize the volume of overland flow per unit area of developed land.
Utilize buffers such as forests and wetlands to protect collection areas and streams from urban impacts.
Divert storm water away from critical features such as steep slopes, unstable soils, or valued habitats.

58. FIS Area - Grand Forks
1992
2001
1984
1974

59. FIS Area – Fargo/Morehead
1992
1974
1984
2001