Water Resources Final - Hydrology and Hydraulics Concepts

Hydrologic Cycle

movement of water through the atmosphere, into/along the ground, and back again

Watershed

land area that channels rainfall and snowmelt to creeks, streams, and rivers, and eventually to outflow points such as reservoirs, bays, and the ocean.

Number of drainage basins in the US

11

Largest Drainage basin in the US

Mississippi-Missouri Drainage Basin

Tributary

Small streams that feed into larger ones

What are the three stream classifications

Perennial, Intermittent, Ephemeral

Perennial Stream

Holds water/flow throughout the year

Intermittent

hold water/flow during wet portions of the year

Ephemeral

hold water/flow only during and directly after rain events/snowmelt

Bankfull Width

the width of the surface of the water at the point where water just begins to overflow into the active flood plain.

Typical return period for a bankfull width flow

1.5 to 2.5 year return period.

Hydrologic Cycle Mass Balance Outputs

ET, Interception (F), Infiltration (I), Sublimation

Hydrologic Cycle Mass Balance Inputs

Precipitation

Of the two most common precipitation types, which is dominant?

Rainfall is the dominant precipitation type

Of the two most common precipitation types, which is secondary?

Snowfall is the secondary precipitation type

Use of Actual Storms

• forensic hydrology

• to determine design storms

• to evaluate a catastrophic event

Use of Design Storms

• identify amount of precip. for a given design in a specific region

• based on analysis of actual storms

Key hydrologic region parameters that define the design storm

1. Depth, P (inches)

2. Storm Duration, D (hours)

3. Antecedent Condition (dry, moist, wet)

Antecedent Condition

how wet the watershed is before a storm event occurs

Ways to characterize P

Depth, Areal Distribution (distribution of of P), Duration, Frequency of Occurrence (P=1/T), Sequence of Events (how does depth vary with time), Geographic Location

Isohyets

Lines of equal rainfall depth on a rainfall distribution map

Intensity

Depth/Duration; typical units are [in/hr]

Hyetograph

graph of intensity or depth over time

Time of Concentration (tc)

the time required for water to travel from the hydraulically most remote part of the basin to the point of interest.

Travel Time (Tt)

the time that it takes water to travel from one point to another.

Parameters for Tc

• Slope

• Watershed size

• Flow resistance (surface roughness)

• Water input (P, i, etc)

Types of Flow

Sheet flow, Overland flow, Shallow Concentrated flow, Channel flow

Rational Method C

Runoff Coefficient

Rational Method Q

Peak Runoff Flow (cfs)

Case where watershed is non-homogeneous: Rational Method

C becomes Cw - Weighted Runoff Coefficient

Centrifugal Pumps

Transports fluids by conversion of rotational kinetic energy to the hydrodynamic energy of the fluid flow.

Examples of Rating Curves

Weirs, Orifices, Culverts - Stage per discharge/flow

What four parameters are balanced when creating a pump curve?

Head, flow, efficiency, and power

Relationship between impeller size and pump head

Larger impellers create more pump head than smaller impellers

Relationship between pump angular speed and pump head

Faster pumps create more head than slower pumps

Operating Point

Point of intersection between a pump curve and a system curve

Flow Classifications

Type 1: Steady Flow

Type 2: Unsteady Flow

Type 3: Uniform Flow

Type 4: Varied Flow

Steady Flow

Flow does not change with time. Flow through one x-section/unit time is equal to another

Unsteady Flow

Flow changes with time. i.e. river hydrograph

Uniform Flow

Flow maintains a constant depth and x-section.

Uniform Flow characteristics

1. Constant slope

2. Constant depth

3. Prismatic channel (constant x-section & bottom slope)

4. No acceleration or deceleration.

Varied Flow types

1. Gradually Varied

2. Rapidly Varied

Rapidly Varied Flow

The flow depth (y) changes abruptly from one point to another in the direction of flow

Hydraulic Control

A man-made structure or a natural channel feature that "controls" the flow of water and sets the water surface elevation both up- and downstream

Examples of natural hydraulic controls

A constriction or riffle crest

Examples of man-made hydraulic controls

A culvert or weir

Gradually Varied Flow

The flow depth (y) changes gradually from one point to another in the direction of flow