A User's Guide - Government of Newfoundland and Labrador
Contents
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3. BAR Barren Area Not Used 20 6 ALS Lakes Swamps Area Not Used 26 9 WARNINGS amp ERROR DIAGNOSIS year 2 Use results with caution 10 These parameters are outside 20 the range for reliable results 50 Eastern amp Southwestern Eastern Southwestern 1 North Central 2 Humber amp Northern Peninsula 3 Range of Mean Annual Runoff for Region 1 1100 mm to 2100 mm km km tt 1 day 368 171 141 95 Parameter Range 40 9 0 22 4 9 0 200 0 62 7 67 2 17 9 Low Flows 5 7 day 443 211 177 154 15 day 553 255 212 181 Northeast River Gauged Site 02ZK002 30 day 791 373 309 264 23 Data Input into LFFE 91 WKI 1 Name of Watershed Enter the name of the watershed for which low flows are being estimated 2 Location of Watershed Three 3 hydrological regions have been identified during the low flow study and are shown in Figure 2 Refer to this figure to determine the region within which the watershed lies Note that Regions A B and C in Figure 2 must be input as 1 2 and 3 in LFFE 91 WKI1 3 DA Area of Watershed This is the drainage area in km of the watershed at the section where low flows need to be estimated It is recommended that the drainage area be determined using a planimeter or digitizer from 1 50 000 topographic maps 4 Forested Area This is the area in of the watershed covered by forests It is r
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5. 0 862 05 30 0 99 0 193 Q20 30 0910 010 30 0 99 0 128 050930 0929 020 30 0 99 0 108 BETAGIS 07362 30 0 98 0 039 Q2 15 0 870 15 0 99 0 133 Q5 15 0712 02 15 0 97 0291 010915 0 858 05 15 0 99 0 169 020415 0902 010 15 0 99 0 134 Q50 15 0917 020 15 0 99 0 130 0 5848 BETA 30 0 96 0 053 02607 0 879 7 0 99 0 094 Q5 7 0715 02 7 0 98 0229 Q10 7 0847 05 7 0 99 0 148 Q20 7 0886 Q1087 0 99 0 127 Q50 7 0894702087 0 99 0 134 04864 BETA30 0 94 0 065 Q2 1 880 0 99 0 086 5 1 0 708 02 1 098 0215 Q10 1 0831 05 1 099 0 136 20 1 0 856 010 1 0 99 0 114 050 1 0867 020 1 099 0 118 Notes BETA N Beta parameter of Gumbel Type III PDF for N day low flow series QT N T year Low Flow Regression Estimate of duration N days RA Correlation coefficient SEB Standard error of estimate QT N log DA Drainage Area km FAR Percentage of drainage area covered by forests 20 It is recommended that the regression equations given in Tables 9 10 and 11 be applied under the following conditions Equations for Region A 1 2 The drainage arca of the watershed must be less than 200 km The percentage of barren area in the watershed must be between 25 and 75 The percentage of forested area must be between 10 and 70 The percentage of watershed area occupied by lakes and swamps must between 10 and 20 Equation
6. River Gauged Site 027K002 Location of watershed 1 Eastern amp Southwestern Eastern Southwestern 1 North Central 2 Humber amp Northern Peninsula 3 Range of Mean Annual Runoft for Region 1 1100 mm to 2100 mm Physiographic Parameters Parameter Range DA Area of watershed 89 8 km 40 200 0 FAR Forested Area X if Unavail 4241 km 90 627 BAR Barren Area Not Used 20 6 km 224 672 ALS Lakes Swamps Area Not Used 26 9 km 90 17 9 WARNINGS amp ERROR DIAGNOSIS T Low Flows 1 5 year 1 day 7 day 15 day 30 day 2 368 443 553 791 Use results with caution 10 171 211 255 373 These parameters are outside 20 141 177 212 309 the range for reliable results 50 95 154 181 264 Table 15 Adjusted Low Flow Estimates at Ungauged Site A Low Flow Estimates at Ungauged Site using Regression Equations l s T Year 1 day 7 day 15 day 30 day 2 337 407 508 727 10 157 194 235 343 20 129 163 195 284 50 87 141 166 242 B Low Flow Estimates at Gauged Site using Regression Equations 1 3 T Year 1 day 7 day 15 day 30 day 2 368 443 553 791 10 171 211 255 373 20 141 177 212 309 50 95 154 181 264 Low Flow Estimates Gauged Site trom Frequency Analysis V s T Year 1 day 7 day 15 day 30 day 2 523 800 1047 10 230 268 325 468 20 180 205 252 388 50 141 154 198 330 Adjusted Low Flow Estimates at Ungauged Site V s AIB C T Yea
7. are outside 0 129 163 195 the range for reliable results 50 87 141 166 30 day 727 343 284 242 32 Case B GAUGING STATION EXISTS ON STREAM The drainage area at the ungauged site DA u 82 6 km B 2 The gauged site on Northeast River is 02ZK002 and is included in Table 2 From Table 2 the drainage area at the gauged site DA g is 89 6 km From Table 1 the number of years of daily flow data n g is 11 B 3 0 85 DA g 76 2 lt DA u 82 6 lt 1 15 DA g 103 and n g 11 gt 7 therefore proceed to Step B 4 B 4 Go through Steps A 1 to for ungauged site These have already been done for Case A above and the regression low flow estimates are given Table 13 5 Go through Steps A 1 to for the gauged site 02ZK002 Since this site is included in Table 2 the physiographic parameters are read as DA 89 6 km FAR 42 1 km BAR 20 6 km and ALS 26 9 km The regression low flow estimates are shown in Table 14 B 6 The gauged site is included in Tables 5 6 7 and 8 The low flow frequency estimates obtained therein are shown in Table 15 B 7 The adjusted low flow estimates at the ungauged site together with the estimates obtained in Steps B 4 B 5 and B 6 are shown in Table 15 Table 14 Low Flow Estimates at Gauged Site 02ZK002 Regional Frequency Estimates of Low Flows for the Island of Newfoundland Name of watershed Northeast
8. as the average daily flow in ms I s over the continuous N day period For design purposes low flows are usually expressed in terms of return periods in years For example a low flow with duration N day magnitude x m s and return period T years is the average flow over N continuous days that one expects to be at or below x m s on the average at least once every T years The particular combination of duration and return period chosen for characterising a low flow is primarily a function of the intended water management or engineering application A report entitled Characteristics and Estimation of Minimum Streamflows for the Island of Newfoundland 1 describing the methodology and results of a frequency analysis of low flows at thirty nine gauging stations on streams in Newfoundland was completed in June 1991 A series of regional regression equations for estimating low flows of several durations and return periods at ungauged sections of streams were derived from the results of the analysis This guide summarizes the results of the study and presents the regional regression equations A computer based approach to using the equations and an example to illustrate their application are then given 2 DATA ON GAUGED WATERSHEDS The analysis of low flows was based on unregulated daily stream flows from 39 gauged watersheds in Newfoundland 2 Figure 1 shows the location of the watersheds and gauging stations Table lists these watershe
9. each identified region evaluating the resulting regression equations and re defining the regions boundaries if necessary The three regions are Avalon and Burin Peninsulas and the Southwest Newfoundland The main characteristics of this region are high precipitation high runoff potential and significant barren areas B North Central Newfoundland The main characteristics of this region are low precipitation low runoff potential and significant forest areas insignificant barren areas c Humber Valley and Northern Peninsula The main characteristics of this region are moderate precipitation moderate runoff potential and moderate forest and barren areas The south coast of the Island was not identified as a region in Figure 2 because of insufficient hydrologic data in the area c REGION SN A Avalon amp Burin Peninsulas and Southwest Newfoundland North Central Newfoundland Humber Valley and Northern Peninsula E s Dt VBS 77 o2vRoo3 102173003 OU TA a 7 p ap E 84 022 002 Gauging Station i Se P 9226001 uda 2 Figure 2 Division of Island into Three Regions for Low Flow Analysis 16 The regression analysis for each region consisted of the following steps 1 Regression analysis between the Beta 30 and watershed characteristics Beta 30 were the beta parameters of the 30 day low fl
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12. used to obtain first estimates of the low flows It may still be necessary to investigate other methods of obtaining the low flows Select the appropriate constants and coefficients from Tables 9 10 and 11 to calculate low flows of the desired return period and region This step is performed automatically by LFFE 91 WK1 and the low flow estimates with return periods of 2 10 20 and 50 years and durations 1 7 15 and 30 days are displayed on the computer screen 27 CASE B Estimating Low Flows at an Ungauged Site Located on a Gauged Stream B 1 B 2 53 B 4 18 5 1 6 Plot ungauged site topographic map delineate the drainage divide and determine drainage area Let area DA u km Plot gauged site on a topographic map delineate the drainage divide and determine drainage area Let area DA g km Obtain the number of years of daily flow data available at gauged site Let n n g If 0 85 DA g lt DA u lt 1 15 DA g and n g gt 7 then goto Step otherwise goto Step 1 case Perform Steps A 1 to for ungauged site Extract low flow estimates of required return period and duration from computer results Perform Steps A 1 to A 6 for gauged site If the gauged site is included in Table 2 then the physiographic parameters DA FAR BAR and ALS listed therein can used Note that FAR BAR and ALS are given as percentages in Table 2 but must be entered a
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16. December and for the winter season which was defined as the period between and including January and June Four durations of low flows were investigated 1 day 7 day 15 day and 30 day The average unit mean low flows during the winter and summer seasons for four geographical regions of the Island are shown in Table 4 Table 4 Average Regional Mean N Day Low Flows Per Unit Area Winter Winter Summer Summer 1 30 day 1 day 30 day Vs km Vsikm V s km V s km Avalon amp Burin 84 20 0 54 11 0 Central 6 5 11 5 31 5 Northern 4 8 6 8 47 73 Southwest Region 5 4 12 6 54 10 5 It is apparent that in most areas summer unit mean low flows are lower than winter unit mean low flows Also the summer unit mean low flows are lowest in the central region of the Island and highest in the eastern part of the Island For the purposes of this guide only the results pertaining to the summer low flows will be presented however the frequency estimates of winter low flows are provided in the main report 1 9 5 FREQUENCY ESTIMATES N DAY LOW FLOWS Calculated summer low flows of four durations 1 day 7 day 15 day and 30 day and for the period of record were used as input data into the Low Flow Frequency Analysis LFA computer program 4 to obtain estimates of low flows with various return periods The LFA program uses the Gumbel Type IH probability density function to statistically model low flows The summer low flow es
17. Estimation of Low Flows for the Island of Newfoundland A User s Guide Government of Newfoundland and Labrador WRD HM 91 IV Department of Environment and Lands Water Resources Division June 1991 ESTIMATION OF LOW FLOWS FOR NEWFOUNDLAND A User s Guide 12 John s Government of Newfoundland and Labrador Department of Environment and Lands Pa Water Resources Division June 1991 SUMMARY The objective of this guide is to provide users with a computer based method of estimating 1 day 7 day 15 day and 30 day low stream flows with return period of 2 10 20 and 50 years for the Island of Newfoundland The significant results of a study on which the estimation technique is based are presented The computer based version of the estimation technique is then described followed by an example to illustrate its application 10 iii TABLE OF CONTENTS Summary List of Tables List of Figures Introduction Data on Gauged Watersheds Regional Characteristics of Runoff Regional Characteristics of N Day Low Flows Frequency Estimates of N Day Low Flows Regression Equations for Estimating N Day Low Flows Computer Based Use of Regression Equations Estimation Procedure Mlustrative Example References iv 0 10 12 13 14 15 iv LIST OF TABLES List of Gauging Stations Included in Study Physiographic Characteristics of Gauged Watersheds Unit Mean Monthly and Ann
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19. ds together with the locations of the gauges the watersheds drainage areas and the record length available for each station A partial listing of the physiographic database on the 39 gauged watersheds with natural flows is shown in Table 2 3 EO S oe os iA ee a 027030 02YK004 Ea X 025003 AN RS 02 5001 2 9221001 0224007 02YN002 f oz v z a T n i 274009 Gauging Station t ine Si Si Figure 1 Locations of Watersheds and Gauging Stations for Low Flow Study z essi IE VE BYN Av H9IH MOTIS SAHHYH LOOrAZO ees ee eve prozeDN S394039 15 HOOUHSIOHS H E JILL 000220 0 east Dove es LOU 0 dOL 7009220 m 02 0009 OSE ZVN AVAMHOIH SIYON IISI 1008220 D ew Ov LL 8S 61 By LPN EYIN 04002 ATLL 5009220 a emi 2880 22 POLYGSM 00 AYMH IH VOVHYO SNYUL LY HJA 200220 n emi 6961 Sriz SM SZPI GDN 3TWAdIH HY3N 100420 oc esel osei vzo 12 36 05N 1094 S 1 lv IN3HMOL 002420 En 1881 6081 ZZSSOSAA tt WHY 10 1 3AOEY WEY LYO 1003420 8 996k 68 BOL 49 BVT YVAN NOO
20. ecommended that the forested area be determined using a planimeter or digitizer from 1 50 000 topographie maps The forested area is used as a predictive parameter in the regression equations for calculating low flows for watersheds in region A only If however the forested area is not available then an x can be entered The alternate regression equation will be used te calculate low flows for region A and a message will appear at the bottom of the screen indicating this case For watersheds in regions B and C the forested area is not used in the regression equations and a message Not Used will appear by the entry cell Nevertheless it is preferable that the forested area be calculated and entered The program will indicate whether this calculated area is 24 within the range used in deriving the equations Hence the user will be able to evaluate the results 5 BAR Barren Area and 6 ALS Lakes Swamps Area The area in km covered by barrens and the area in km covered by lakes and swamps are not required for calculating low flow estimates However it is recommended that these areas be extracted and entered so that it can be determined whether they are within the applicable range This is especially important for watersheds located in region B In this region all but one of the watersheds used in the analysis were less than 3 barren Hence if the ungauged watershed has a much higher proportion of barren area the low
21. etermined to be 37 5 km The barren area BAR was determined to be 19 5 km The area of lakes swamps ALS was determined to be 25 6 km A 4 The values from Steps A 2 and were input into LFFE 91 WK1 A 5 The parameters BAR and ALS were outside their applicable ranges ALS was significantly higher than its upper limit Since neither parameter is used in estimating low flows the regression equations can still be used but some caution is necessary in using the results A 6 The required low flow estimates at the ungauged site together with the input parameters are shown in Table 13 which is a copy of the worksheet as displayed on the computer screen Table 13 Low Flow Estimates at Ungauged Site Regional Frequency Estimates of Low Flows for the Island of Newfoundland Name of watershed Northeast River Ungauged Site Location of watershed 1 Eastern amp Southwestern Eastern Southwestern 1 North Centrai 2 Humber amp Northern Peninsula 3 Range of Mean Annual Runoff for Region 1 1100 mm to 2100 mm Physiographic Parameters Parameter Range DA Area of watershed 82 6 km 40 2000 FAR Forested Area X it Unavail 37 5 km 83 578 BAR Barren Area Not Used 19 5 km 207 619 ALS Lakes Swamps Area Not Used 25 8 km 8 8 16 5 WARNINGS amp ERROR DIAGNOSIS T Low Flows year 1 day 7 day 15 day 2 337 407 508 Use resuits with caution 10 157 194 235 These parameters
22. flow estimates could be seriously in error OUTPUT OF PROGRAM The program outputs the 2 10 20 and 50 year expected low flows of durations 1 7 15 and 30 day in litres per sec l s The program also outputs the range of the mean annual runoff in mm expected for the particular region within which the watershed is located A copy of the worksheet as illustrated in Table 12 can be obtained by pressing the Print Screen or by using Lotus 1 2 3 print commands 25 8 ESTIMATION PROCEDURE The procedural steps given below for estimating low flows using the regression equations should be treated as guidelines Specific situations warrant that professional engineering judgement as appropriate to site watershed conditions be exercised in the application of the procedure For example large scale logging groundwater contribution from outside the watershed s topographic divide and artificial regulations and diversions can severely affect the applicability of the procedure A detailed description on the application of the regional regression equations using LFFE 91 WK1 to estimate low flows at ungauged sections of streams is given below as Case A Occasionally a hydrometric station will be located on the subject stream If the watershed area at the ungauged site is less than 15 smaller or larger than the watershed area at the gauged site and the number of years of daily flow data at the gauged section is equal to or greate
23. included in the study 29 9 ILLUSTRATIVE EXAMPLE The illustrative example has been designed in such a way that Case A of an ungauged site on an ungauged stream and Case B of an ungauged site on a gauged stream can be described for the same ungauged site Problem Definition Low flow estimates of return periods 2 10 20 and 50 years and durations 1 7 15 and 30 days are required at an ungauged site on the Northeast River near Placentia This site is about 3 km above an existing gauging station 02ZK002 In the first instance in Case A it will be assumed that the gauging station does not exist on the stream and only the regression equations will be used to determine the low flow estimates Then in Case B using the known frequency estimates of low flows at the gauging station the low flows at the site will be re estimated to illustrate the adjustment process Case A ASSUME GAUGING STATION DOES NOT EXIST ON STREAM A 1 The topographic divide of the watershed to the ungauged site was delineated on a 1 50 000 topographic map The forest barren lakes and swamps areas were identified and marked A 2 Referring to Figure 2 it was determined that the watershed is located in the Burin Peninsula ie Region In LFFE 91 WK1 this information is entered as Region 1 A 3 the required areas were determined using a digitizer The drainage area DA was determined to be 82 6 km 30 The forested area FAR was d
24. ntage of drainage area covered by forests Regression equation with only DA as the predictive parameter 18 Table 10 Regression Equations for Region B Equation SEE BETA 30 5 0466 083 0 184 Q2 30 0844 30 0 99 0101 Q5 30 0 566 02 30 0 97 0 102 010930 0588 05 30 0 99 0 032 020930 0 393 010 30 0 77 0 062 050030 0 602 020 30 0 88 0 022 BETA 15 0 4046 BETA 30 0 99 0 047 92 15 0 841 15 0 99 0 081 5 15 0 543 02 15 0 98 0 070 Q10815 0 542 05 15 0 98 0 034 020015 02870106015 0 24 0 073 Q50 15 0 695 020 15 0 99 0 004 BETA 7 0 2280 BETA 30 0 98 0 075 Q2 7 0 834 7 0 99 0 072 Q5 7 0352650297 0 98 0 063 01087 0 529 05 7 0 98 0 033 Q20 7 0280 010 7 0 21 0 070 05067 0 694 020 7 0 99 0 004 01449 BETA30 0 98 0 077 Q2 1 0 826 BETA 1 0 99 0 064 Q5 1 0 509 Q2 1 0 98 0 057 Q10 1 0 518 05 1 0 98 0 031 Q20 1 0275 010 1 0 19 0 065 Q50 1 0 670 020 1 0 99 0 004 Notes BETA N Beta parameter of Gumbel Type PDF for N day low flow series QT N T year Low Flow Regression Estimate of duration N days R Correlation coefficient SEE Standard error of estimate QT N log BETA N DA Drainage Area km FAR Percentage of drainage area covered by forests 19 Table 11 Regression Equations for Region Equation R SEE BETA 30 DA 0 85 0 093 Q2 30 0 859 0 99 0247 Q5 30 0701 02 30 095 0 449 0106030
25. ntry cells are unprotected cells and are differentiated on the screen Any attempt to enter characters in protected cells will result in a beep indicating an illegal entry Pressing the Esc key will abort the attempted change in a protected cell Messages will appear on the screen whenever the user is to be made aware of certain information For example whenever watershed parameters are outside their applicable range or area of watershed is less than other entered areas or an unacceptable input for watershed location has been entered a message will appear in the lower left hand corner of the screen indicating the error Whenever the message Not Used appears by an entry cell it means that this particular parameter is not used in calculating the low flow estimates and entering numbers for this parameter will not change the results However it is recommended that such parameters be evaluated and input so that the program can indicate whether they are within the applicable range This wil give the user more information on which to assess the validity of the results Lotus 1 2 3 is a U S registered trademark of Lotus Development Corporation Table 12 Example of Spreadsheet as Displayed on Computer Screen Regional Frequency Estimates of Low Flows for the Island of Newfoundland Name of watershed Location of watershed 1 T Physiographic Parameters DA Area of watershed 89 6 FAR Forested Area X if Unavail 42 1
26. ow series as calculated by LFA 4 One regression equation was derived for each region 2 Regression analysis between Beta 30 and Beta N where N 1 7 and 15 Beta N were the beta parameters of the N day low flow series as calculated by LFA Three regression equations N 1 7 15 were obtained for each region 3 Regression analysis between Beta N and Q2 N Q2 N and Q5 N 5 and Q10 N Q10 N and Q20 N and Q20 N and Q50 N QT N was the T year N day low flow estimate as calculated by LFA The analysis was done for each region and low flow duration The equations resulting from regression analyses are given in Tables 9 10 and 11 for regions A B and C respectively The equations for Beta 30 for the three regions show that Beta 30 is primarily dependent on drainage area in region A Beta 30 depends slightly on the percentage of forested area The equation for region A when percentage of forested area is excluded from the analysis is also shown in Table 9 This equation can be used for estimating low flows in region A when only the drainage area is available as the predictive parameter A comparison of the low flow trequency estimates with the estimates obtained from applying the regression equations on the gauged watersheds indicates that the percentage difference between the frequency and regression estimates in most cases ranged from 50 to 50 although some were much higher The high values occurred most often for low flows wi
27. r 1 day 7 day 15 day 30 day 2 479 589 735 962 10 211 246 300 430 20 165 189 232 357 50 129 141 182 303 35 Neither the illustration of the procedure in the above example nor the suggested procedural steps given for estimation of low flows are intended to be exhaustive Rather the intent has been to merely demonstrate the application of the procedure through worked examples Therefore it is recommended that professional engineering judgement should be exercised in specific applications 2 3 10 REFERENCES Characteristics and Estimation of Minimum Streamflows for the Island of Newfoundland Newfoundland Department of Environment and Lands Water Resources Division 1991 HYDAT Surface Water Data Volume 2 0 1988 Environment Canada Water Resources Branch 1990 Compilation of Physiographic Data for Flood Frequency Analysis 1982 Hydrometeorologic and Physiographic Data Abstraction for the Island of Newfoundland An Update 1989 Newfoundland Department of Environment and Lands Water Resources Division Low Flow Frequency Analysis Program LFA Condie R and Cheng L C Environment Canada Water Resources Branch 1977 LFFE 91 WK1 Regional Frequency Estimates of Low Flows for the Island of Newfoundland using Lotus 1 2 3 Newfoundland Department of Environment and Lands Water Resources Division 1991
28. r than 8 then a method to estimate low flows at the ungauged site using the information at the gauged section is given as Case B An example to illustrate the procedural steps is given CASE Estimating Low Flows at an Ungauged Site A 1 Plot site on a topographic map and delineate the drainage divide It is recommended that 1 50 000 National Topographic Series maps be used for delineating the watershed boundary A 2 Refer to Figure 2 and determine the hydrologic region within which the subject basin is located A3 A4 5 6 26 Estimate Physiographic Parameters DA FAR BAR ALS Determine watershed area DA forest area FAR barren area BAR and area of lakes and swamps ALS all in km using a planimeter or a digitizer and 1 50 000 topographic maps Input Name of Watershed Step A 1 Location of Watershed Step A 2 and physiographic parameters Step A 3 into worksheet Check whether or not the parameters fall within the specified ranges for which the equations are considered to be applicable These ranges are automatically displayed on the computer screen besides the entry cells If any parameter value used in the regression equation falls well outside the specified range it is suggested that other methods of obtaining low flows be investigated If the parameter value is only slightly outside the specified range or if it is not a parameter used in estimating low flows the equations can be
29. s for Region B 1 The drainage area of the watershed must be between 40 km and 400 km The percentage of barren area in the watershed must be less than 5 The percentage of forested area must be greater than 80 with the rest of the watershed occupied by lakes and swamps Equations for Region C 1 3 The drainage area of the watershed must be between 240 km and 600 km The percentage of barren area in the watershed must be between 10 and 40 The percentage of forested area must be between 40 and 65 The percentage of the watershed occupied by lakes and swamps should be between 10 and 20 21 7 COMPUTER BASED USE OF REGRESSION EQUATIONS Manual calculations of low flow estimates using the regression equations in Tables 9 10 and 11 require tedious substitutions of watershed characteristics and regression coefficients This increases the chances of errors To eliminate this source of errors a Lotus 1 2 3 worksheet LFFE 91 WK1 5 has been developed to perform the calculations automatically once the watershed s name geographical location and physiographic parameters are input The results are displayed instantly on the screen A copy of the package is available from Director Water Resources Division Department of Environment and Lands P O Box 8700 St John s Newfoundland 1 4 6 A typical spreadsheet as displayed when the Lotus worksheet LFFE 91 WK1 is loaded is illustrated in Table 12 The e
30. s km in LFFE 91 WK1 Extract low flow estimates of required return period and duration trom computer results Conduct a single station flood frequency analysis on data at gauged site A method for conducting single station frequency analyses is given in the report 1 If the gauged site has been included in Tables 5 6 7 and 8 then 28 use the results given in the Tables Abstract the low flows for the required return periods and durations B 7 Adjust low flow estimates at ungauged site results of Step B 4 with low flow estimates at gauged site results of Steps B 5 and B 6 The adjustment includes the effects arising due to differences in drainage areas DA and if the watershed is in region A forested area FAR The equation used to adjust the low flow estimates is as follows QT N Site Regression Adjusted vr Gauge Regression xQT M Gauge Frequency where QT N Site Adjusted is the adjusted T year and N day low flow estimate at the site OQT N Site Regression is the T year and N day low flow estimate at the site obtained by using the regression equations Step B 4 QT N Gauge Regression is the T year and N day low flow estimate at the gauging station obtained from the regression equations Step B 5 QT N Gauge Frequency is the T year and N day low flow estimate at the gauging station obtained from a frequency analysis of recorded flows or from Tables 5 6 7 and 8 if the gauging station was
31. seco voro t990 2000420 9100 0200 7 100 220 9100 so o 1004 420 509 p sevo EUG AZG 3250 1280 ust sso eL LooHzzo sso E seri vert sez 1009220 veso voro vig soz 1009720 soso soro Mot LE s 200220 vszo p 290 sovi su 009220 sero s9vo n eot aee 2003220 soro 6920 esso gos 9090 ees 100NZZ0 evoo D ezo ee zooHzzo tooo saro sero ee 009220 e200 oeoo 5800 001220 1000 2000 9000 9100 soanzzo ew CAD Ore uy 2020 SO 20 obeumig SM0 4 MO 0 Jo Kouenbej4 gejqer 14 6 REGRESSION EQUATIONS FOR ESTIMATING N DAY LOW FLOWS Regression analysis is a multi variate analysis in which the low flow frequency estimates from gauged watersheds are related quantitatively to independent physiographic characteristics of the watersheds The resulting equations can be used to estimate low flow characteristics at sites with inadequate hydrologic information The best regression equations were obtained when the Island was divided into three 3 regions and the regression analysis performed in each region separately The regions are shown in Figure 2 The division of the Island was the outcome of an iterative process of identifying regions with distinct hydrological climatic and physiographic characteristics performing regression analyses for
32. sland tend to have the lower unit mean monthly flows On a temporal basis the higher unit mean monthly flows tend to occur between the months of April and June which corresponds to the snowmelt season The lower unit mean monthly flows occur during two periods one between January and March i e during the winter season prior to snowmelt and the other between July and September i e during the summer season when there are usually higher losses due to increased evapotranspiration rates ioo 600 0 oroo esoo soo zoo isoo 0500 409 000 6500 800 000 600 100220 oroz saoo 0800 100 1900 200 00 peot 3900 900 00 0900 moez 2000720 0607 9970 sevo Groo 00 400 900 zoro oso 2 1900 200 oo ooo Zz00 9900 vera it00 ceti 009220 ont E zwo woo ewo 0800 C200 orzi 5 00 osoo 900 000 3200 6100 600 soo iro 2200 1000 esoo 200 1009420 oc stoo Boo poo peoo 900 509 400 9700 moo sioa 100440 or 00 4200 ciwo soo isoo itoo 900 100 oee oni too soo o0 osoo 00 zoo 00
33. th high return periods that is when the frequency estimates were close to zero The high percentage differences were due to the fact that for very low flow estimates the differences between the regression and frequency estimates became very close to the frequency estimates themselves 17 Table 9 Regression Equations for Region A Equation R SEE BETA 30 14 8594 DA FAR 921 0 97 0 113 30 49774 DAU 0 96 0 133 Q2 30 0 832 BETA 30 0 99 0 049 Q5 30 0 610 Q2 30 0 96 0 104 Q10 30 0 773 Q5 30 0 97 0 081 Q20 30 0 829 Q10 30 0 96 0 081 Q50 30 0 853 20 30 0 94 0 099 15 0 6699 BETA 930 9 0 99 0 059 Q2 15 0 833 BETA I15 0 99 0 036 Q5 15 0 605 02 15 0 96 0 080 010 15 0 764 05 15 0 97 0 057 Q20 15 0 829 010 15 0 96 0 052 Q50 15 0 853 Q20 15 0 94 0 062 BETA 7 0 5236 BETA 30 0 99 0 077 Q2 7 0 831 BETA 7 0 99 0 029 5 7 0 610 02 7 0 95 0 072 Q10 7 0 781 Q5 7 0 96 0 053 Q20 7 0 840 Q10 7 0 96 0 048 Q50 7 0 866 Q20 7 0 94 0 057 BETA 1 0 4198 BETA30 5 0 98 0 100 Q2 1 0 831 BETA L 0 99 0 024 Q5 1 0 606 Q2 1 0 97 0 049 1 0 769 Q5 1 0 97 0 038 20 1 0 822 Q10 1 0 96 0 038 Q50 1 0 676 020 1 080 0 078 Notes Beta parameter of Gumbel Type 1U PDF for N day low flow series QT N T year Low Flow Regression Estimate of duration N days R Correlation coetticient SEE Standard error of estimate OT N log BETAGN DA Drainage Area FAR Perce
34. timates with return periods 2 5 10 20 and 50 years are shown in Table 5 1 day Table 6 7 day Table 7 15 day and Table 8 30 day tort 999 ore boorazo 1960 En 9 ere 2 0 zoro ure m 5 oez 2000210 zeco soi 9 soz 1008220 ws o 90 En eti t00vZz0 5 200 220 serz siot ire 1007420 15 E veo 1000 20 zevi 092 E he 1003420 9 629 2901 n 5 3950 1960 5 1050 ori 1000420 0000 9000 EI 5 2000 2 0000 0000 2000 500 E 00WAzO ases 453 onze E 1000420 E ev tora a 1003220 eu n vaez E 9 Loosaza asiz ore tory 1004720 0000 I zao vez 5 LE p E ZOONAZO 1200 oroo 490 ET euo vero 008 10 0 3600 seio seo 5 eocoAzo 2000 vooo 6000 ero 5 toorzz0 0000 0000 Loodaze 20 0 5 sizo vivo 0 90 E 100220 sso ovo 5 100 220 EI owo tero sel 1009720 wo 2009220 100 2600 seo 5 5009220 osgo 150 2004720 1800 eero sero oro 9 2320 sieo sso 5 1004220 soro 1200 sro 9 200 2500 8900 5 009220 5000 3000 9000 roo 2007220 0000 1000 2000 i00 s 2 0 we re a 2 0 Jaquin 0
35. ual Flows at Gauging Stations Average Regional Mean N Day Low Flows Per Unit Area Frequency Estimates of Summer 1 day Low Flows Frequency Estimates of Summer 7 day Low Flows Frequency Estimates of Summer 15 day Low Flows Frequency Estimates of Summer 30 day Low Flows Regression Equations for Region A Regression Equations for Region B Regression Equations for Region C Example of Spreadsheet as Displayed on Computer Screen Low Flow Estimates at Ungauged Site Low Flow Estimates at Gauged Site 022 002 Adjusted Low Flow Estimates at Ungauged Sire 10 12 v LIST OF FIGURES Page Locations of Watersheds and Gauging Stations for Low Flow Study 3 Division of Island into Three Regions for Low Flow Analysis 15 1 INTRODUCTION The characteristics and estimation of low flows are important for several water resources engineering and management applications such as estimating available water supply for municipal and industrial uses determining the waste water effluent dilution potential of a receiving stream predicting the impact of stream diversions on the minimum flow requirements for spawning and migrating fish and generally for environmental impact assessment studies An annual low flow condition is defined as a period during which the average streamflow is a minimum for the year The duration of the low flow is usually measured in days and is expressed as an N day low flow period The magnitude of the low flow is expressed
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