WR Lab Final

Three factors that determine how much water flows in a watershed?

1. climate - amount of precipitation and seasonal variation impacts watershed volume

2. land cover - affects runoff/land absorption

3. topography - affects runoff and infiltration

What is the difference between “watershed” and “USGS Hydrologic units?”

a watershed is a physical topographic feature of land that drains water to a point

USGS Hydrologic Units is an administrative classification system that is based on watershed features and uses numbered units to break down regions

all Hydrologic units represent watersheds, but not all watersheds are classified as a USGS Hydrologic Unit.

“Hydrodynamic entry length" definition; what physical change marks its completion?

 The distance from the inlet of a pipe or duct to the location where the flow becomes fully developed; the merging of the wall boundary layers at the pipes center

What is the phenomenon generated by the sudden closure of a valve?

water hammer/hydraulic shock

How do viscous and inertial forces determine whether a fluid flows in a laminar flow?

Viscous forces - creates internal friction within a fluid, resisting motion and opposing changes in the fluid's flow behavior; helps maintain the fluid’s structure and limit its tendency to move freely.

Inertial forces - drives the movement of the fluid and encourages mixing and instability.

What natural processes would affect pipe roughness? 

1. Corrosion

2. Chemical Reactions

3. Surface treatments and protective coatings

4. Welding or extrusion

What effect would rougher pipe materials (concrete, clay, etc.) have on the velocity profile?

Increases turbulence which influences the velocity profile and pressure distribution within the pipe

List and describe the process commonly referred to as rainfall abstractions

Process that delays the rainfall becoming surface runoff

interception, evaporation, transpiration, depression, detention, and infiltration

What key assumptions of the Rational Method (Q = CiA) restrict its applicability

The drainage area is no larger than 200 acres and does not account for storage in the drainage area

The peak flow occurs when runoff is resulting from the entire watershed, the rainfall intensity is uniform at the critical time, and the peak flow recurrence interval is equal to the rainfall intercity recurrence interval.

What are the two primary mechanisms that generate overland flow?

Infiltration-excess overland flow/Hortonian flow (occurs when rain falls faster than the soil can absorb it)

Saturation-excess overland flow (occurs when the soil is already completely filled with water)

Explain the concept of water budget

List and describe each variable included in the water budget.

A water budget is a way to account for how water moves into, out of, and is stored in a system like a watershed, lake, or groundwater basin.

Precipitation (P) - main input of the water into the system (infiltrate into the soil, run off the surface, evaporate, or be stored)

Evapotranspiration (ET) - loss of water to the atmosphere and includes evaporation and transpiration (water released from during photosynthesis)

Runoff (Q) - water that flows over the land surface and eventually enters the streams and rivers

Change in storage (S) - represents the increase or decrease in water stored in the system.

Explain the difference between steady and unsteady open-channel flow, and uniform and nonuniform (varied) flow.

steady flow - flow parameters like velocity, depth, and discharge do not change with time at a given point

Unsteady flow - flow parameters change with time at a given point

Uniform flow - flow parameters like depth, velocity, and slope remain constant along the length of the channel

Non uniform flow - flow parameters change along the channel and can be due to changes in the channel geometry, slope, roughness, or external inflows and outflows

Define hydraulically “smooth” and “rough” flows

Smooth - movement of water near the channel surface is controlled mostly by viscosity

 Rough - bumps and roughness of the channel surface have a bigger effect on the flow

How is the specific energy “E” defined?

The energy per unit weight of water measured with respect to the channel bottom

What is the energy grade line (EGL), and why is it useful in hydraulic analysis?

A graphical representation that shows the total energy per unit weight of a fluid particle as it moves along a streamline in a fluid flow system

Combines the effects of both potential and kinetic energy, which is used for analyzing the energy distribution in open channel flow

When is a hydraulic jump generated in an open channel?

When fast, shallow water suddenly changes into slower and deeper water

 two limitations of the HEC-RAS model.

inability to perform water quality modeling in a 2D flow area

inability to provide a hydrologic model

Flood management tools that use HEC-RAS results are…

Floodplain zoning

Flood mitigation measures

Hydraulic modeling

FIRM 2D modeling

What types of flow analysis can be performed using HEC-RAS?

one dimensional steady flow

one/two dimensional unsteady flow

Quasi unsteady or fully unsteady flow movable boundary sediment transport computations

What is the role of Manning’s roughness coefficient in HEC-RAS modeling?

influences the flow resistance, velocity, flow depth, and flood extent in the models; accounts for energy friction losses.

Define and establish the difference between a dam, a weir, and a barrage

weir: a fixed barrier used to raise the water level on the upstream side and regulate flow.

barrage: a complex system that uses gates to regulate the height of the water in larger bodies of water.

dam: an immovable barrier designed to store water creating a basin.

What is a compound weir?

a complex hydraulic system that combines 2 or more weir types to measure and control water more effectively

Three common structural flood control measures are…

1. Dams: holds water back in a reservoir

2. Levees: contains the flow of water in a defined channel, and prevents floodwaters from spreading outside this channel

3. Flood Gates: moveable barriers that can open or close; controls the flow of water through channels of water

Two limitations of HEC-HMS

1. simplified model formation that allows for the system to run simulations quickly

2. simplified flow representation

 main components of HEC-HMS

Basin Model

Meteorologic Model

Control Specifications

hydrologic studies HEC-HMS suitable for

1. flood hydrology to model both riverine and urban flooding

2. water availability studies

3. stormwater runoff from rainfall events

4. simulate reservoir inflows

5. analyzing sediment transport and debris flow

difference between "event" and "continuous" models in HEC-HMS

event: focuses on a single storm, showing how runoff responds during that event including peak flow and timing, without accounting for changes between storms

continuous: simulates multiple storms over a longer period and tracks changes in soil moisture, groundwater, and baseflow

Would an urban or rural environment have more runoff?

Urban environment

A steep terrain would have a(n) _______ runoff, and a flat terrain would have a(n) _______ infiltration time.

Accelerated

Greater