Hydrology

SANJU'S BLOG

Civil engineer 

Hydrology

Hydrographs

🔸 Hydrograph a Plot between discharge in a stream and time in chronological order.

🔸 Factors affecting flood Hydrograph

1. Shape of basin :

👉 Fan shaped catchment give high peak, narrow Hydrograph

👉 Fern shaped catchment give low peak, broad Hydrograph

2. Slope : Steeper slope catchment gives large peak discharge.

3. Drainage density : It is ratio of Total channel length to the total drainage area.

4. Stream density : It is the ratio of number of streams to area of basin.

5. Form factor : It is the ratio of basin area to square of basin length.

🔸 Direct runoff Hydrograph (DRH) : The surface runoff Hydrograph obtained after the base flow separation is called DRH.

🔸 Effective Rainfall = Total Rainfall - Total losses

🔸 Effective Rainfall Hydrograph (ERH) : The Hyetograph obtained after subtracting Initial loss and infiltration losses is called ERH.

🔸 Unit Hydrograph : It defined as direct runoff Hydrograph resulting from one unit depth (1 cm) of Rainfall excess occurring uniformly over the basin and at a uniform rate for a specified duration.

🔸 Instantaneous unit Hydrograph : It is infinitely small duration & of unit rainfall excess

🔸 The upper limit on the area of the basin for the applicability of unit Hydrograph is generally taken to be 5000 Sq.km.

🔸 Kirpich equation is used to determine time of concentration in runoff Hydrograph.

🔸 Clark's method aims to developing an 1 UH due to a instantaneous rainfall excess over catchment.

🔸 The concept of unit Hydrograph was first introduced by Sherman

🔸 The concept of distribution graph was first suggested by Bernard

🔸 Isochrone is a line joining the points of equal time of flow.

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Hydrology

Food routing

🔸 Flood routing : It is Technique of determining the flood Hydrograph at a section of a river or channel by utilising the data of flood flow at one or more upstream sections.

🔸 Methods of routing

👉 Hydrologic flood routing : It is based on equation of continuity only

👉 Hydraulic of routing : It is based on equation of continuity and momentum. In hydraulic routing basic differential equations known as St. Venant equation

🔸 Lag is the time difference between peaks of inflow and outflow hydrograph.

🔸 Muskingham method is a Hydrologic channel routing Method

🔸 Muskingham method - weighing factor X is between 0 to 0.5

🔸 A linear reservoir is one in which the storage varies linearly with the outflow rate

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Hydrology

Well hydraulics

🔸 Aquifer

👉 Aquifer is the saturated formation which not only stores water but also yield sufficient quantity.

👉 Ex. Unconsolidated deposits of sand &gravel forms aquifer

🔸 Aquitard

👉 Aquitard is the saturated formation through which only seepage is possible but it's yield is insufficient. It is partly permeable in nature.

👉 Ex:-Sandy-clay unit.

🔸 Aquiclude

👉 It is geological formation which is essentially impermeable to the flow of water.

👉 Ex:- Clay.

🔸 Aquifuge

👉 It is geological formation which neither contains water nor transmits through it.

👉 Ex:- Massive compacted rock without fractures.

♦️ Types of aquifer

1. Unconfined aquifer : Also known as water table aquifer. 

2. Confined aquifer (Artesian aquifer) : An aquifer confined between two impervious beds such as aquicludes or aquifuge.

🔸 The voume of water that can be extracted by force gravity form a unit volume of aquifer material is called specific yield

🔸 The discharge per unit drawdown at a well known as specific capacity

🔸 The unit of intrinsic permeability is Sq.cm

🔸 Storage coefficient (S) is dimensionless

🔸 Specific yield (Sy) + Specific retention (Sr) = Porosity

🔸 For open wells the ratio of safe depression head to critical depression head is 1/3

🔸 The ratio of water level change to atmospheric pressure head is called barometric efficiency.

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Hydrology

River gauging

🔸 River gauging involves the measurement of discharge of a river and the establishment of gauge post on one its banks.

🔸 The levels of water in a stream are taken by means of gauge post

🔸 Coconut is most suitable for use as surface float for measuring velocity in a river

🔸 The velocity of a stream obtained by using rod is the mean velocity

🔸 The science and practice of water flow measurement is known as hydrometry.

🔸 The slope area method is extensively used in estimation of flood discharge based on high water marks

🔸 The dilution Method of stream gauging is used measuring discharges in steady flow in a small turbulent stream.

🔸 Mean velocity with current meter at depth

👉 One point method : 0.6d

👉 Two point method : 0.2d to 0.8d

👉 Three point method : 0.2d, 0.6d & 0.8d

🔸 To obtain mean velocity of flow in a stream, the velocity determine by float is multiplied by factor equal to 0.85

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Building construction

Basic elements of pitched roof

1. Span : It is the clear distance between the supports of an arch, beam or roof truss.

2. Rise : It is the vertical distance between the top of the ridge and the wall plate 

3. Pitch : It is the inclination of the sides of a roof to the horizontal plane. 

4. Ridge : It is defined as the apex line of the sloping roof.

5. Eaves : The lower edge of the inclined surfaces is called eaves. From eaves, the rain water from the roof surface drops down

6. Hip : It is the ridge formed by the intersection of two sloping surfaces, where exterior angle is greater than 180°

7. Valley : It is a reverse of a hip. It is formed by the intersection of two roof Surfaces, making an external angle less than 180°. 

8. Hipped end : It is the sloped triangular surface formed at the end of a roof.

9. Verge : The edge of a gable, running between the eaves and ridge, is known as a verge. 

10. Ridge piece or ridge beam or ridge board : It is the horizontal wooden member, in the form of a beam or board, which is provided at the apex of a roof truss. It supports the common rafters fixed to it. 

11. Common rafters or Spars : These are inclined wooden members running from the ridge to the eaves. Depending upon the roof covering material, the rafters are Spaced 30 to 45 cm centre to centre. 

12. Purlins : These are horizontal wooden or steel members, used to support common rafters of a roof when span is large. Purlins are supported on trusses or walls.

13. Hip rafters : These are the sloping rafters which form the hip of a sloped roof

14. Battens : These are thin strips of wood, called scantling, which are nailed to the rafters for lying roof materials above.

15. Boardings : They act Similar to battens and are nailed to common rafter to support roofing material.

16. Template : This Is a square or rectangular block of stone or concrete placed under a beam or truss, to spread the load over a larger area of the wall. 

17. Cleats : These are short sections of wood or steel (angle iron), which are fixed on the principal rafters of trusses to support the purlins.

18. Truss : A roof truss is a frame work, usually of triangles, designed to support the roof covering or ceiling over rooms.

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