CE 3354 Engineering Hydrology Lecture 9 Rational Equation

  • Slides: 40
Download presentation
CE 3354 Engineering Hydrology Lecture 9: Rational Equation Method Introduction to HEC-HMS

CE 3354 Engineering Hydrology Lecture 9: Rational Equation Method Introduction to HEC-HMS

Outline l ES-4 Solutions l Rational Equation Method l Introduction to HEC-HMS

Outline l ES-4 Solutions l Rational Equation Method l Introduction to HEC-HMS

ES 4 Solution l Solution sketch on-line l Go through and discuss each part

ES 4 Solution l Solution sketch on-line l Go through and discuss each part of the sketch, and demonstrate software as necessary http: //www. rtfmps. com/ce 3354 -2015 -3/3 -Homework/ES-4/ce 3354 -es 4 solution/cd 3354 -es 4 -solution-sketch. pdf

Rational Equation Method l The rational method is a tool for estimating peak discharge

Rational Equation Method l The rational method is a tool for estimating peak discharge from relatively small drainage areas. (Mulvaney, 1850; Kuichling, 1889) l CMM pp. 496 -502

Assumptions l Rainfall area. is distributed uniformly over the drainage l Rainfall intensity is

Assumptions l Rainfall area. is distributed uniformly over the drainage l Rainfall intensity is uniform throughout the duration of the storm. l Response time for the drainage area is less than the duration of peak rainfall intensity.

Assumptions l The rational method does not account for storage in the drainage area.

Assumptions l The rational method does not account for storage in the drainage area. Available storage is assumed to be filled. l The calculated runoff is directly proportional to the rainfall intensity. l The frequency of occurrence for the peak discharge is the same as the frequency of the rainfall producing that event.

Typical Limitations l Drainage areas less than 200 acres (some jurisdictions allow up to

Typical Limitations l Drainage areas less than 200 acres (some jurisdictions allow up to 640 acres) l Minimum duration is prescribed to prevent “infinite intensity” at short times – typically 10 minutes (some jurisdictions allow 5 minutes) l No substantial storage (or all storage filled)

Typical Procedure (1) Area Less than 200 acres? (2) Estimate Tc (3) Design Intensity

Typical Procedure (1) Area Less than 200 acres? (2) Estimate Tc (3) Design Intensity for ARI EBDLKUP-2015; NOAA-14 (4) Estimate C (5) Compute Qp=Ci. A (6) Validate/verify

Calculation Sheet

Calculation Sheet

Runoff Coefficients l CMM p. 498

Runoff Coefficients l CMM p. 498

Runoff Coefficients l Texas Hydraulic Design Manual

Runoff Coefficients l Texas Hydraulic Design Manual

Runoff Coefficients l Oregon Hydraulics Manual – Values similar in most sources

Runoff Coefficients l Oregon Hydraulics Manual – Values similar in most sources

Time of Concentration l The value of Tc is important in rational method for

Time of Concentration l The value of Tc is important in rational method for estimating rainfall intensity. l It is also used in other hydrologic models to quantify the watershed response time

Time of Concentration l Time of concentration (Tc) is the time required for an

Time of Concentration l Time of concentration (Tc) is the time required for an entire watershed to contribute to runoff at the point of interest for hydraulic design l Tcis calculated as the time for runoff to flow from the most hydraulically remote point of the drainage area to the point under investigation.

Time of Concentration l Travel time and Tc are functions of length and velocity

Time of Concentration l Travel time and Tc are functions of length and velocity for a particular watercourse. l. A long but steep flow path with a high velocity may actually have a shorter travel time than a short but relatively flat flow path. l There may be multiple paths to consider in determining the longest travel time. l The designer must identify the flow path along which the longest travel time is likely to occur.

Time of Concentration l Various l On Methods to Estimate Tc the server in

Time of Concentration l Various l On Methods to Estimate Tc the server in readings: CMM pp. 500 -501 has several formulas l HDS-2 pp. 2 -21 to 2 -31 has formulas and examples l LS pp. 196 -198 has several formulas l

Time of Concentration l Examine l l l 3 Methods to Estimate Tc NRCS

Time of Concentration l Examine l l l 3 Methods to Estimate Tc NRCS Upland Kerby-Kirpich NRCS Velocity Method l Similar in scope; depend on distances, slope, and land surface conditions. Module 3

NRCS Upland Methdod l Specify flow path l Determine cover on flow path l

NRCS Upland Methdod l Specify flow path l Determine cover on flow path l Determine slope(s) along path l Partition into different cover types and slopes along path l Apply velocity model on each part add times for entire path

Upland Method Velocity Chart

Upland Method Velocity Chart

Kerby-Kirpich Method for Estimating Tc l Appropriate l Compute for many conditions up to

Kerby-Kirpich Method for Estimating Tc l Appropriate l Compute for many conditions up to two times: overland flow time and channel flow time

Kerby-Kirpich Method for Estimating Tc l Overland l Channel flow time l Combine the

Kerby-Kirpich Method for Estimating Tc l Overland l Channel flow time l Combine the two to estimate time of concentration (if there is no channel component, then omit) l Overland length < 1200 feet

Kerby-Kirpich Method for Estimating Tc Kerby Retardance Coefficient Generalized Terrain Condition Dimensionless Retardance Coefficient

Kerby-Kirpich Method for Estimating Tc Kerby Retardance Coefficient Generalized Terrain Condition Dimensionless Retardance Coefficient (N) Pavement . 02 Smooth, bare, packed soil . 10 Poor grass, cultivated row crops, or moderately rough packed surfaces . 20 Pasture, average grass . 40 Deciduous forest . 60 Dense grass, coniferous forest, or deciduous forest with deep litter . 80

NRCS Method for estimating Tc l Comprised of up to three components l The

NRCS Method for estimating Tc l Comprised of up to three components l The sheet and shallow concentrated are of importance in urban systems. Module 3

NRCS Method for estimating Tc DDF Atlas; NOAA 14

NRCS Method for estimating Tc DDF Atlas; NOAA 14

NRCS Method for estimating Tc

NRCS Method for estimating Tc

NRCS Method for estimating Tc

NRCS Method for estimating Tc

NRCS Method for estimating Tc

NRCS Method for estimating Tc

Example l Figure to right is a Google-Earth image of a 550 acre watershed

Example l Figure to right is a Google-Earth image of a 550 acre watershed in Virginia l The area is agricultural, Virginia SH 58 runs along the south part of the watershed. The other visible roads are county roads or private (farm) roads.

Example l Figure to right is a topographic map of the same area, but

Example l Figure to right is a topographic map of the same area, but without the watershed boundary depicted. l The outlet is the red square on the map. The yellow square is a reference area of 1000 X 1000 meters.

Example l Watershed delineated l Main channel delineated l Overland paths indicated

Example l Watershed delineated l Main channel delineated l Overland paths indicated

Example l Acrobat. Pro measure reference area and watershed area l Acrobat. Pro measure

Example l Acrobat. Pro measure reference area and watershed area l Acrobat. Pro measure main channel length l Acrobat. Pro measure overland length

Example l Use Kerby-Kirpich to estimate Tc l Report as Tc =67 minutes

Example l Use Kerby-Kirpich to estimate Tc l Report as Tc =67 minutes

33 Introduction to HEC-HMS l History l l Evolved from HEC-1 as part of“new-generation”

33 Introduction to HEC-HMS l History l l Evolved from HEC-1 as part of“new-generation” software circa 1990 Integrated user interface to speed up data input and enhance output interpretation l HMS l l is a complex and sophisticated tool Intended to be used by a knowledgeable and skilled operator Knowledge and skill increase with use

34 HEC-HMS l Data l l Graphical User Interface (GUI) Multiple input files Multiple

34 HEC-HMS l Data l l Graphical User Interface (GUI) Multiple input files Multiple output files Time-series in HEC-DSS l All l l management files arranged in a “Project” Paths to individual files Can e-mail entire project folders and have them run elsewhere

35 HEC-HMS l Conceptualizes precipitation, watershed interaction, and runoff into major elements l l

35 HEC-HMS l Conceptualizes precipitation, watershed interaction, and runoff into major elements l l l Meterological model l Raingage specifications and assignment to different sub-basins Time-series models l Supply input hyetographs l Supply observed hydrographs Simulation control l Supply instructions of what, when, how to simulate

36 HEC-HMS l Conceptualization: l l l Basin and sub-basin description l Supply how

36 HEC-HMS l Conceptualization: l l l Basin and sub-basin description l Supply how the system components are interconnected Loss model l Supply how rainfall is converted into excess rainfall Transformation model l Supply how the excess rainfall is redistributed in time and moved to the outlet

37 Applications l HEC-HMS is a Hydrologic Model l Peak Flows l Hydrograph Routing

37 Applications l HEC-HMS is a Hydrologic Model l Peak Flows l Hydrograph Routing l Stream reaches l Reservoirs and detention basins l Hydrograph lagging and attenuation l Sub-basin modeling (if appropriate)

38 HEC-HMS l Precipitation l Abstractions l Fraction of precipitation that does not contribute

38 HEC-HMS l Precipitation l Abstractions l Fraction of precipitation that does not contribute to runoff (and ultimately discharge) l Routing l l l Watershed routing Stream (Channel) routing Reservoir (Storage) routing

HEC-HMS Example l Minimal model l SCS Type Storm l 640 acre watershed –

HEC-HMS Example l Minimal model l SCS Type Storm l 640 acre watershed – no process models; completely converts rainfall into runoff l Illustrate how to mimic rational method by adjusting drainage area l Repeat with a 24 -hour Texas Hyetograph same location

Next Time l l Loss Processes l Evapotranspiration l Infiltration SCS Curve Number

Next Time l l Loss Processes l Evapotranspiration l Infiltration SCS Curve Number