Category:749 Hydrologic Analysis - Revision history

Smithk: /* 749.5.4 Rainfall Intensity */Per BR, updated the Central District IDF curve

2019-04-23T20:04:32Z

749.5.4 Rainfall Intensity: Per BR, updated the Central District IDF curve

← Older revision		Revision as of 15:04, 23 April 2019
Line 359:		Line 359:
	:[[media:749 IDF NE.docx\|Northeast District]]		:[[media:749 IDF NE.docx\|Northeast District]]
	:[[media:749 IDF KC.docx\|Kansas City District]]		:[[media:749 IDF KC.docx\|Kansas City District]]
	:[[media:749 IDF Cen.docx\|Central District]]		:[[media:749 IDF Cen 2019.docx\|Central District]]
	:[[media:749 IDF SL.docx\|St. Louis District]]		:[[media:749 IDF SL.docx\|St. Louis District]]
	:[[media:749 IDF SW.docx\|Southwest District]]		:[[media:749 IDF SW.docx\|Southwest District]]

EPGsysop: Per BR, revised Time of Concentration equation guidance by providing optional combination of Kirby-Hathaway & Kirpich equations and adding the optional low slope factor presented in the new research.

2018-04-05T14:07:50Z

Per BR, revised Time of Concentration equation guidance by providing optional combination of Kirby-Hathaway & Kirpich equations and adding the optional low slope factor presented in the new research.

Show changes

Smithk: /* 749.6.2.1 Equations */ correction

2015-06-17T13:47:28Z

749.6.2.1 Equations: correction

← Older revision		Revision as of 08:47, 17 June 2015
Line 571:		Line 571:
	\|align="center"\| 2 \|\|align="center"\| 188A<sup>0.599</sup>10<sup>0.014(I)</sup> \|\|align="center"\| -23.1 to 30.0		\|align="center"\| 2 \|\|align="center"\| 188A<sup>0.599</sup>10<sup>0.014(I)</sup> \|\|align="center"\| -23.1 to 30.0
	\|-		\|-
	\|align="center"\|5 \|\|align="center"\| 352A<sup>0.~~59210~~</sup><sup>0.011(I)</sup>\|\| align="center"\| -20.6 to 25.9		\|align="center"\|5 \|\|align="center"\| 352A<sup>0.592</sup>10<sup>0.011(I)</sup>\|\| align="center"\| -20.6 to 25.9
	\|-		\|-
	\|align="center"\|10\|\|align="center"\| 484A<sup>0.~~59410~~</sup><sup>0.010(I)</sup>\|\| align="center"\| -19.6 to 24.4		\|align="center"\|10\|\|align="center"\| 484A<sup>0.594</sup>10<sup>0.010(I)</sup>\|\| align="center"\| -19.6 to 24.4
	\|-		\|-
	\|align="center"\|25\|\| align="center"\| 671A<sup>0.~~5990~~.008(I)</sup>\|\| align="center"\| -19.6 to 24.4		\|align="center"\|25\|\| align="center"\| 671A<sup>0.599</sup>10<sup>0.008(I)</sup>\|\| align="center"\| -19.6 to 24.4
	\|-		\|-
	\|align="center"\|50\|\| align="center"\| 826A<sup>0.~~6040~~.008(I)</sup>\|\| align="center"\| -20.6 to 25.9		\|align="center"\|50\|\| align="center"\| 826A<sup>0.604</sup>10<sup>0.008(I)</sup>\|\| align="center"\| -20.6 to 25.9
	\|-		\|-
	\|align="center"\|100\|\|align="center"\| 991A<sup>0.~~6080~~.007(I)</sup>\|\|align="center"\| -22.3 to 28.7		\|align="center"\|100\|\|align="center"\| 991A<sup>0.608</sup>10<sup>0.007(I)</sup>\|\|align="center"\| -22.3 to 28.7
	\|-		\|-
	\|align="center"\|500\|\|align="center"\| 1,420A<sup>0.619</sup>10<sup>0.006(I)</sup>\|\|align="center"\| -28.9 to 40.7		\|align="center"\|500\|\|align="center"\| 1,420A<sup>0.619</sup>10<sup>0.006(I)</sup>\|\|align="center"\| -28.9 to 40.7

Smithk at 13:43, 17 June 2015

2015-06-17T13:43:05Z

← Older revision		Revision as of 08:43, 17 June 2015
Line 325:		Line 325:
	:[[media:749 IDF SW.docx\|Southwest District]]		:[[media:749 IDF SW.docx\|Southwest District]]
	:[[media:749 IDF SE.docx\|Southeast District]]		:[[media:749 IDF SE.docx\|Southeast District]]


	==749.6 USGS Regression Equations==		==749.6 USGS Regression Equations==

Smithk: minor corrections

2015-06-17T13:40:00Z

minor corrections

Smithk: /* 749.11.3 Flow Combinations */

2015-06-16T17:13:53Z

749.11.3 Flow Combinations

← Older revision		Revision as of 12:13, 16 June 2015
Line 1,162:		Line 1,162:
	For streams that are within the influence reach of the confluent streams backwater the procedure provided in [http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_w199.pdf NCHRP 199], ''Estimating Joint Probabilities of Design Coincident Flows at Stream Confluences'', produces a probability based estimate for combinations of return periods for confluent streams that will produce the maximum water surface elevation and/or velocity for a design flood event. An excerpt below from NCHRP 199 provides information on which cases this procedure is applicable to (Note: For Case A this procedure may still be useful to determine flow downstream of the junction based on flow combinations).		For streams that are within the influence reach of the confluent streams backwater the procedure provided in [http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_w199.pdf NCHRP 199], ''Estimating Joint Probabilities of Design Coincident Flows at Stream Confluences'', produces a probability based estimate for combinations of return periods for confluent streams that will produce the maximum water surface elevation and/or velocity for a design flood event. An excerpt below from NCHRP 199 provides information on which cases this procedure is applicable to (Note: For Case A this procedure may still be useful to determine flow downstream of the junction based on flow combinations).

	[[~~media~~:749.11.3.jpg\|center\|~~950px~~]]		[[image:749.11.3.jpg\|center\|750px]]

	==749.12 References==		==749.12 References==

Smithk: /* 749.11.1 Coincident Peaks */

2015-06-16T17:12:49Z

749.11.1 Coincident Peaks

← Older revision		Revision as of 12:12, 16 June 2015
Line 1,148:		Line 1,148:
	FEMA, ''Guidelines and Specifications for Flood Hazard Mapping Partners'', Appendix C: Guidelines for Riverine Flood Analysis and Mapping gives the following guidance on when coincident peaks are appropriate to use:		FEMA, ''Guidelines and Specifications for Flood Hazard Mapping Partners'', Appendix C: Guidelines for Riverine Flood Analysis and Mapping gives the following guidance on when coincident peaks are appropriate to use:

	[[image:749.11.1.jpg\|center\|~~950px~~]]		[[image:749.11.1.jpg\|center\|750px]]

	===749.11.2 Exclusive Peaks===		===749.11.2 Exclusive Peaks===

Smithk: /* 749.11.1 Coincident Peaks */

2015-06-16T17:12:29Z

749.11.1 Coincident Peaks

← Older revision		Revision as of 12:12, 16 June 2015
Line 1,148:		Line 1,148:
	FEMA, ''Guidelines and Specifications for Flood Hazard Mapping Partners'', Appendix C: Guidelines for Riverine Flood Analysis and Mapping gives the following guidance on when coincident peaks are appropriate to use:		FEMA, ''Guidelines and Specifications for Flood Hazard Mapping Partners'', Appendix C: Guidelines for Riverine Flood Analysis and Mapping gives the following guidance on when coincident peaks are appropriate to use:

	[[~~media~~:749.11.1.jpg\|center\|950px]]		[[image:749.11.1.jpg\|center\|950px]]

	===749.11.2 Exclusive Peaks===		===749.11.2 Exclusive Peaks===

Smithk: /* 749.10.1.2 Stage-Discharge Curve */

2015-06-16T17:11:18Z

749.10.1.2 Stage-Discharge Curve

← Older revision		Revision as of 12:11, 16 June 2015
Line 1,045:		Line 1,045:

	:where: Q = discharge, ft<sup>3</sup>/s		:where: Q = discharge, ft<sup>3</sup>/s
	:C = broad-crested weir coefficient (see [[Media:749 Broad-Crested Weir Coefficients.pdf\|Broad-Crested Weir Coefficients]]		:C = broad-crested weir coefficient (see [[Media:749 Broad-Crested Weir Coefficients.pdf\|Broad-Crested Weir Coefficients]])
	:L = broad-crested weir length, ft		:L = broad-crested weir length, ft
	:H = head above weir crest, ft., measured at least 2.5H upstream of the weir		:H = head above weir crest, ft., measured at least 2.5H upstream of the weir

Smithk: /* 749.5.2.4 Composite Runoff Coefficients */

2015-06-16T17:05:54Z

749.5.2.4 Composite Runoff Coefficients

← Older revision		Revision as of 12:05, 16 June 2015
Line 234:		Line 234:

	====749.5.2.4 Composite Runoff Coefficients====		====749.5.2.4 Composite Runoff Coefficients====
	The land use and soil type may vary from one portion of a watershed to another. In this case an average runoff coefficient, weighted by area, should be used. For example, consider a flat watershed with soils of average infiltration capacity (soil group B) and with 1/3 of the drainage area cultivated (C=0.40) and 2/3 of the drainage area in woodland cover (C=0.20). The weighted average runoff coefficient to be used to estimate the 10-year flood is.		The land use and soil type may vary from one portion of a watershed to another. In this case an average runoff coefficient, weighted by area, should be used. For example, consider a flat watershed with soils of average infiltration capacity (soil group B) and with 1/3 of the drainage area cultivated (C=0.40) and 2/3 of the drainage area in woodland cover (C=0.20). The weighted average runoff coefficient to be used to estimate the 10-year flood is:

	<math>C=[(0.40)(1/3)+(0.20)(2/3)]/1.0=0.267\,</math>		:<math>C=[(0.40)(1/3)+(0.20)(2/3)]/1.0=0.267\,</math>

	The frequency correction factor may be applied to the weighted average runoff coefficient to estimate lower frequency flows: in the above example, a "C" value of (1.10)(0.267)=0.294 would be used for the 25-year flood, and a "C" of (1.20)(0.267)=0.320 would be used for the 50-year flood.		The frequency correction factor may be applied to the weighted average runoff coefficient to estimate lower frequency flows: in the above example, a "C" value of (1.10)(0.267)=0.294 would be used for the 25-year flood, and a "C" of (1.20)(0.267)=0.320 would be used for the 50-year flood.

← Older revision		Revision as of 15:04, 23 April 2019
Line 359:		Line 359:
	:[[media:749 IDF NE.docx\|Northeast District]]		:[[media:749 IDF NE.docx\|Northeast District]]
	:[[media:749 IDF KC.docx\|Kansas City District]]		:[[media:749 IDF KC.docx\|Kansas City District]]
	:[[media:749 IDF Cen.docx\|Central District]]		:[[media:749 IDF Cen 2019.docx\|Central District]]
	:[[media:749 IDF SL.docx\|St. Louis District]]		:[[media:749 IDF SL.docx\|St. Louis District]]
	:[[media:749 IDF SW.docx\|Southwest District]]		:[[media:749 IDF SW.docx\|Southwest District]]

← Older revision		Revision as of 08:40, 17 June 2015
Line 87:		Line 87:
	The Rational Method may be used on rural watersheds smaller than 200 acres. On watersheds larger than 200 acres, the USGS Regression Equations should be used. The 2014 USGS Rural Regression Equations may be used for Watersheds that lie in Region I and Region II if the drainage area is greater than 70 acres and 110 acres respectively. Watersheds that lie within Region III for the 2014 USGS Rural Regression Equations and have drainage areas between 200 to 1350 acres do not fall within the limits for either set of equations. In this case one of the following approaches may be used:		The Rational Method may be used on rural watersheds smaller than 200 acres. On watersheds larger than 200 acres, the USGS Regression Equations should be used. The 2014 USGS Rural Regression Equations may be used for Watersheds that lie in Region I and Region II if the drainage area is greater than 70 acres and 110 acres respectively. Watersheds that lie within Region III for the 2014 USGS Rural Regression Equations and have drainage areas between 200 to 1350 acres do not fall within the limits for either set of equations. In this case one of the following approaches may be used:

	:a. Use an alternate method such as ~~Flood Hydrographs <link to EPG~~ 749.9>;		:a. Use an alternate method such as [[#749.9 Flood Hydrographs\|Flood Hydrographs]];
	:b. for drainage areas greater than 300 acres use the 1995 USGS Rural Regression Equations;		:b. for drainage areas greater than 300 acres use the 1995 USGS Rural Regression Equations;
	:c. for drainage areas between 200 and 300 acres calculate the peak rate of runoff using the Rational Method and the 1995 USGS Rural Regression Equations, and use the one that is most appropriate.		:c. for drainage areas between 200 and 300 acres calculate the peak rate of runoff using the Rational Method and the 1995 USGS Rural Regression Equations, and use the one that is most appropriate.
Line 323:		Line 323:
	:[[media:749 IDF Cen.docx\|Central District]]		:[[media:749 IDF Cen.docx\|Central District]]
	:[[media:749 IDF SL.docx\|St. Louis District]]		:[[media:749 IDF SL.docx\|St. Louis District]]
	:[[media:749 IDF SW.docx\|~~Souththwest~~ District]]		:[[media:749 IDF SW.docx\|Southwest District]]
	:[[media:749 IDF SE.docx\|Southeast District]]		:[[media:749 IDF SE.docx\|Southeast District]]

Line 537:		Line 537:

	=====749.6.1.2.3 Limitations of Equations=====		=====749.6.1.2.3 Limitations of Equations=====
	The USGS Rural Regression Equations may be used to estimate magnitude and frequency of floods on most Missouri streams Caution should be used when using these equations when the drainage area and slope are outside of the limits of the Valid Data Ranges shown in EPG ~~794~~.6.1.2 1995 Rural Regression Equations.		The USGS Rural Regression Equations may be used to estimate magnitude and frequency of floods on most Missouri streams Caution should be used when using these equations when the drainage area and slope are outside of the limits of the Valid Data Ranges shown in [[#749.6.1.2 1995 Rural Regression Equations\|EPG 749.6.1.2 1995 Rural Regression Equations]].

	However, the equations are generally not applicable for:		However, the equations are generally not applicable for:
Line 607:		Line 607:
	One statistical parameter computed in the Log-Pearson analysis is the skew coefficient of the distribution of the stream gage data. Skew coefficients for the data from stream gages in Missouri are typically between -0.1 and -0.4 when sufficient years of record are available. Skew coefficients outside this range may indicate an insufficient length of record or an analysis affected by outliers in the data. In this case, other methods of determining discharges will likely provide better estimates.		One statistical parameter computed in the Log-Pearson analysis is the skew coefficient of the distribution of the stream gage data. Skew coefficients for the data from stream gages in Missouri are typically between -0.1 and -0.4 when sufficient years of record are available. Skew coefficients outside this range may indicate an insufficient length of record or an analysis affected by outliers in the data. In this case, other methods of determining discharges will likely provide better estimates.

	===749.7.2 ~~Ungaped~~ Sites Near Stream Gage===		===749.7.2 Ungaged Sites Near Stream Gage===
	Stream gage data from gages at some distance from the site on the same watershed and stream gage data from nearby hydrologically similar watersheds may also be used to estimate discharges. Discharges obtained from this type of data should be compared with discharges obtained by other methods and not given the same weight as discharges obtained from data from a stream gage at the proposed site. Better estimates of discharge using this method may be obtained by repeating the procedure for several nearby gages and averaging the results. This method should not be used when drainage areas differ by more than 50% or at sites more than 50 miles from the stream gage(s).		Stream gage data from gages at some distance from the site on the same watershed and stream gage data from nearby hydrologically similar watersheds may also be used to estimate discharges. Discharges obtained from this type of data should be compared with discharges obtained by other methods and not given the same weight as discharges obtained from data from a stream gage at the proposed site. Better estimates of discharge using this method may be obtained by repeating the procedure for several nearby gages and averaging the results. This method should not be used when drainage areas differ by more than 50% or at sites more than 50 miles from the stream gage(s).

Line 680:		Line 680:
	Substituting the equation for I<sub>a</sub> into the equation above, the NRCS rainfall-runoff equation becomes:		Substituting the equation for I<sub>a</sub> into the equation above, the NRCS rainfall-runoff equation becomes:

	:<math>Q=\frac{(P-0.2S)^2}{P+0.8S}</math> ~~(Equation 8)~~		:<math>Q=\frac{(P-0.2S)^2}{P+0.8S}</math>

	It is important to note that while both P and Q are given in units of depth, they actually represent volumes of rainfall and runoff, respectively. This is because the indicated depth of rainfall or runoff is assumed to be applied uniformly to the entire watershed area.		It is important to note that while both P and Q are given in units of depth, they actually represent volumes of rainfall and runoff, respectively. This is because the indicated depth of rainfall or runoff is assumed to be applied uniformly to the entire watershed area.
Line 699:		Line 699:
	\| colspan="6" text align="center"\| ''Fully Developed Urban Areas (Vegetation Established)''		\| colspan="6" text align="center"\| ''Fully Developed Urban Areas (Vegetation Established)''
	\|-		\|-
	\| colspan="6"\| Open Space (lawns, parks, golf courses, ~~cemetaries~~, etc.)<sup>3</sup>		\| colspan="6"\| Open Space (lawns, parks, golf courses, cemeteries, etc.)<sup>3</sup>
	\|-		\|-
	\| text align="center"\| Poor Condition (grass cover<50%) \|\| \|\|68 \|\|79 \|\|86 \|\|89		\| text align="center"\| Poor Condition (grass cover<50%) \|\| \|\|68 \|\|79 \|\|86 \|\|89
Line 957:		Line 957:

	:t<sub>p</sub> = time to peak, hrs		:t<sub>p</sub> = time to peak, hrs
	:~~t<sub>r</sub>~~ = duration of rainfall (unit hydrograph duration) = 0.133 t<sub>c</sub>, hrs		:ΔD = duration of rainfall (unit hydrograph duration) = 0.133 t<sub>c</sub>, hrs
	:t<sub>c</sub> = time of concentration, hrs		:t<sub>c</sub> = time of concentration, hrs