Test 1 Flashcards

Question

What are the steps for creating a thiessen

Answer 1

1. Connect Each Raingage use dashed lines. 2. Create a bisect line perpendicular to each dashed line. 3. Extend our bisect lines to the watershed boundary. 4. Connect bisect lines.

Answer 2

• Municipal water supply • Water rights allocation • Reservoir operations • Hydropower • Agriculture/Irrigation • Planning/Drought • Recreation • Water Supply • Designing hydraulic structures • National Weather Service – flood forecasting!

Answer 3

- Union Major - Lost arm at Battle of Shiloh - 1890’s - Professor at Illinois - Expedition to survey the west - Went down the Grand Canyon/Lake Powell - Became 2nd Director of USGS

Answer 4

1889 Embudo NM of the Rio Grande

Answer 5

7,000 gages and 50,000 flow measurements a year

Answer 6

rate at which a volume of water passes through a cross-sectional area

Answer 7

Gaging rod+ Current meter Dye/tracer test Float method ADCP (acoustic doppler current profiling) (Most accurate)

Answer 8

Difference between peak rainfall and peak discharge

Answer 9

Samaria in 5,000 BC

Answer 10

Represents stage discharge relationship Used to convert water level readings into flow rates

Answer 11

Water transformed from liquid phase to vapor phase

Answer 12

Water moves through plants and evaporates through leaves.

Answer 13

Soil Type, Soil Moisture Content, Temp, Humidity, Wind, Cloud Cover

Answer 14

type of Vegetation, Growth Stage

Answer 15

Pan designed to measure evaporation by monitoring loss of water over time (1 day).

Answer 16

1) Hydrologic processes are random. 2) Use statistics to interpret data, Describe random variables using Probability Distribution 3) Identify best fitting distribution that is used to Predict future events.

Answer 17

A countable # of distinct values. Ex: # of children in a family # of flow probes in a lab # of students in a class

Answer 18

- An infinite # of possible values. Ex: Measurements: height, weight, etc. Streamflow

Answer 19

The average time between events [storms, floods, etc.] that equal or exceed a certain magnitude

Answer 20

The probability that a T-year storm event will not occur in n years.

Answer 21

Probability that a T-year storm will occur at least once in n years

Answer 22

Initial Abstraction before runoff can occur such as surface/ depression storage and interception

Answer 23

Entry of water into soil. Impacts the amount of runoff

Answer 24

1.Soil Type 2. Soil Moisture 3. Surface Condition 4. Vegetation 5. Rainfall Intensity 6. Slope

Answer 25

maximum rate of infiltration happens when rainfall is heavy

Answer 26

all of the water seeps into the ground

Answer 27

Physically based, semi- empirical. • One of the most realistic models of infiltration available to engineers. • Originally derived in 1911 by Green and Ampt and then Phillip in 1954 improved it giving it a more physical basis. -Analytical model that has a physical basis to soil properties -non linear can be solved in a spreadsheet format -wetting front travels through soil -can account of unsteady rainfall (reality)

Answer 28

• Best for soils that exhibit a sharp wetting front, ie. course soils w/uniform pore shapes

Answer 29

Horton (1940) observed the infiltration begins at a rate and decays to a final rate -Empirical -nonlinear and can be solved in a spreadsheet format -infiltration in measured by a first order mathematical expression

Answer 30

Assumes rate of infiltration is a function of time and follows a first order decay. • Must have field derived data.

Answer 31

Used when both flow data & corresponding rainfall hyetograph are available. -An index only -Intensity can be taken uniformly over the storm duration -can provide nonlinearly depending on index

Answer 32

1.Calculate volume of direct runoff (rd) 2. Assume number of intervals (M) that contribute to runoff. 3. Calculate the sum of observed rainfall (Rm) in each interval. (∑𝑅𝑅𝑚𝑚) 4. Calculate Phi(∅): ∑𝑅𝑅𝑚𝑚−𝑟𝑟𝑑𝑑 𝑀𝑀(∆𝑡𝑡) 5. Check Phi versus each interval for excess precipitation (Pe) 6. Iterate if necessary 7. Check Pe = rd

Answer 33

– Assessing impact of hydrologic events – Determining values for key variables (Qpeak, stage, precipitation, etc.) – Design system to perform adequately

Answer 34

Hydrologic Design Process- 1. Select Design Storm 2. Predict Runoff 3. Route Flow 4. Evaluate flow at Point(s) of Interest 5. Design System (e.g. structures) 6. ITERATE!

Answer 35

Estimated Limiting Value - largest magnitude possible for a hydrologic event at a given location based on the best available hydrologic information

Answer 36

estimated greatest depth of precipitation for a given duration that is physically possible and reasonable characteristic over a particular geographic location at a certain time of year; depth of rain.

Answer 37

spatial and temporal distribution of the PMP; rain over time.

Answer 38

greatest possible flood assuming complete coincidence of all factors that would produce the heaviest rainfall and maximum runoff; derived from PMS (and therefore PMP); frequency (return period) cannot be determined- some apply arbitrarily high values but they have no physical basis.

Answer 39

helps to understand, predict, and manage water resources by looking at the limiting value of the design

Answer 40

curves representing a localized relationship among intensity, duration, and frequency (return period).

Answer 41

greatest storm that may be reasonably expected.

Answer 42

design flood; estimated using rainfall-runoff modeling by applying unit hydrograph methods to the SPS

Answer 43

rainfall frequency atlas of the eastern United States for duration for 30 minutes to 24 hours and return periods from 1 to 100 years; yields depth of rainfall.

Answer 44

rainfall frequency atlas of the United States for duration for 5 minutes to 60 day and return periods from 1 to 1000 years; yields depth of rainfall.

Answer 45

Most widely used peak runoff method; been around since the 1800’s

Answer 46

1.Entire catchment is contributing to runoff 2. Rainfall is distributed uniformly over the catchment area 3. All hydrologic losses in the catchment are homogeneous and uniform Represented in Runoff Coefficient, C.

Answer 47

1. Used on catchments smaller than ~100 Acres 2. Provides only 1 point on the Runoff Hydrograph (Peak) When using in complex subcatchments it overestimates the actual flow...results in oversized infrastructure. No means to generate or route hydrographs through detention facilties. 3. Routing must be incorporated as we design from point to point.

Answer 48

Time for entire watershed to contribute to runoff.(Single drop of water from the most remote point)

Answer 49

shallow, unconcentrated and irregular flow down a slope does not exceed 300 meters

Answer 50

flow that gains speed and increases depth, forming small channels

Answer 51

1. Obtain runoff coefficient (C) and Manning’s n values for each land cover type (from tables) 2. Determine areas of each land use type 3. Determine time of concentration for each possible flow path a. Determine P2 from TP-40 b. Determine V from TR-55 Figure 3-1 c. Use TR-55 worksheet to: i. Calculate tc’ for sheetflow (first 300 feet of flow path) ii. Calculate t0 for shallow concentrated flow (remaining distance of the flow path) 4. Choose the longest time of concentration (it might not be the flow path you expect it to be!) 5. Use that time on the regionalized IDF curve to find the rainfall intensity (i) 6. Plug all values into Q = kCiA

Answer 52

1) Select Return Period 1 ≤t ≤ 100-Yrs 2) Select precipitation duration [flood depth] 3) Apply NRCS Temporal Distribution pgs. 425-426 30 min →24 hour →Tp 40 4) Multiply your rain depth by distribution.

Answer 53

• Rainfall Intensity • Rainfall Duration • Watershed size • Watershed slope • Watershed shape • Watershed storage • Watershed morphology • Channel type • Land Use/Cover • Soil Type • Percent Impervious

Answer 54

Idea introduced by Sherman in 1932. – Most widely used method of estimating runoff hydrographs • A direct runoff hydrograph resulting from a unit depth (1” or 1cm) of excess precipitation (Pe) over a drainage area at a constant rate. • A linear model that transforms excess precipitation into direct runoff.

Answer 55

Assumptions: 1. Pe constant intensity 2. Pe uniform over watershed 3. Base time resulting from Pe is constant 4. Ordinates of all DRH of common base time are proportional 5. Hydrograph from Pe reflects unchanging characteristics of watershed

Answer 56

Integration: storm hydrograph, baseflow, and watershed area are known. - Scale DRH Deconvolution: storm hydrograph, baseflow, and precipitation data are known. - Matrix methods Synthetic Methods: several options, most used NRCS.

Answer 57

The Curve Number quantifies the watershed response to rainfall.

Answer 58

Land Use • Soil Type • Antecedent Runoff Conditions (ARC)

Answer 59

Wetness of the soil (corrects for moisture)

Answer 60

Normal (No correction)

Answer 61

• Simple • Need Hyetograph • Need Streamflow Data (Vol of Direct Runoff) • Need Watershed Area • CONSTANT Loss • No Ia

Answer 62

Not as simple • Need Hyetograph • Need CN – Land Use – Soils – Watershed Area – Moisture Content • VARIABLE Loss • Ia

Answer 63

NRCS developed this method from the average shape of a large number of UHGs from small agricultural watersheds throughout the U.S. • Allows us to create a UHG for anywhere in the U.S. with minimal data. • Convert NRCS Dimensionless UHG to actual hydrograph by determining Qpeak and Tpeak and multiplying.

Test 1 Flashcards

(91 cards)