Floods in Nebraska on Small Drainage Areas Magnitude and Frequency
GEOLOGICAL SURVEY CIRCULAR 45S Floods in Nebraska on Small Drainage Areas, Magnitude and Frequency By Emil W. Beckman and Norman E. Hutchison
Prepared in cooperation with the Nebraska Department of Roads
GEOLOGICAL SURVEY CIRCULAR 458
Washington 7962 United States Department of the Interior STEW ART L. UDALL, SECRETARY
Geological Survey THOMAS B. NOLAN, DIRECTOR
Free on application to /he U.S. Geological Survey, Washington 25, D. C. CONTENTS
Page Page Abstract ______1 Flood-frequency analysis Cont. Introduction _. ______1 Regional flood-frequency analysis___ 11 Description of area ______1 Base period ______11 Phy siography______1 Definition of mean annual flood ___ 11 Soil.______1 Homogeneity of records______12 Climate ______2 Composite frequency curves ______12 Drainage areas ______3 Relations of mean annual flood____ 12 Causes of floods______3 Hydrologic areas-______14 Flood records available ______3 Application of regional flood-frequency Flood-frequency analysis______9 data ______16 Flood frequency at a gaging station _ _ 9 Tributary areas of natural runoff -__ 16 Value ______9 Stage of flood discharge ______16 Types of series ______9 Maximum known floods______17 Plotting position--- ______10 Summary ______32 Historical data ______10 Selected references __j.______32 Fitting frequency curves ______10 Limitations of a single-station analysis ______10
ILLUSTRATIONS
Page Figure 1. Generalized areas of soil sources in Nebraska_____--_____------_-_- 2 2. Map of Nebraska showing location of gaging stations used in flood-frequency analysis ______9 3. Frequency of annual floods, Plum Creek near Smithfield, Nebr.______10 4. Map of Nebraska showing flood-frequency regions and hydrologic areas ______12 5. Composite frequency curves of annual floods, regions A and B, period 1947 59 _ 13 6. Variation of mean annual flood with contributing drainage area in hydrologic areas 1 10______14 7. Relation of maximum discharge to 10 and 25-year floods, region A, areas 1 and 2 ______28 8. Relation of maximum discharge to 10 and 25-year floods, region A, areas 3 and 4 ______29 9. Relation of maximum discharge to 10 and 25-year floods, region A, areas 5 and 6 ______30 10. Relation of maximum discharge to 10 and 25-year floods, region A, area 7_____ 31 11. Relation of maximum discharge to 10 and 25-year floods, region B, areas 8, 9, and 10 ______32
TABLES
Page Table 1. Period of record of annual peaks at gaging stations------4 2. Maximum stages and discharges at gaging stations ______18 3. Unusual peak discharges at miscellaneous sites and at short-term gaging stations with contributing drainage areas of 300 square miles or less ______26
III Flcxxis in Nebraska on Small Drainage Areas, Magnitude and Frequency
By Emil W. Beckman and Norman E. Hutchison
ABSTRACT Geological Survey, under the direction of Floyd F. LeFever, district engineer, Surface Flood hazard information is needed for small streams as well as for large ones. This report explains methods of de Water Branch, in cooperation with the Ne fining the magnitude and frequency of floods in Nebraska on braska Department of Roads. Financial as uncontrolled and unregulated streams which have about 300 sistance in the preparation of the report was square miles or less of drainage area contributing to sur face runoff. Composite frequency curves defined for two given by the Bureau of Public Roads. flood regions express a ratio of floods with recurrence in tervals ranging from 1.1 to 25 years to the mean annual flood. Curves for 10 hydrologic areas were defined to show the relation of the mean annual flood to the contributing DESCRIPTION OF AREA drainage area. A flood-frequency curve can be drawn from these two sets of curves for any site in the State within the range of drainage area and recurrence interval that is de PHYSIOGRAPHY fined by the base data and not materially affected by the works of man. The two sets of curves are based on all Nebraska has an expansive, gently rolling available pertinent data from records of 5 or more years' duration. to rough topography, broken in places by low hills, a few isolated buttes, mesas, ravines, This report includes a tabulation of maximum flood peaks and several relatively shallow, major streams at gaging stations used and at a number of miscellaneous sites which have less than 300 square miles of contributing which flow in an easterly direction. drainage area. The altitude of the State ranges from 835 feet at the extreme southeast corner to a INTRODUCTION maximum of 5,340 feet at the western border. The land surface slopes rather consistently When loss of life is not a factor, it is gen to the southeast with an average decline of erally not economically sound to design about 9 feet per mile. structures in or across streams for the maximum flood that may occur. Economic The small streams of Nebraska have a wide considerations will dictate the choice of a variation in slope depending on the topography design frequency. An evaluation of these of their drainage basins. The average fall for economic factors is beyond the scope of this individual streams used in this report ranges report. It should be noted that the recurrence from about 6 to about 110 feet per mile. The interval of a flood does not imply any regu major streams fall from 4 to 8 feiet per mile. larity of occurrence. For an example, at any site, two 2 5-year floods may occur in consec utive weeks or such a flood may not occur in SOIL a period of 50 years. Most of the soil mantle of Nebraska origi The purpose of this report is to describe nated from four major sources. The general methods by which the magnitude and fre location of these soils is shown on figure 1, quency of floods may be determined for most which is based on reports by the Nebraska sites in Nebraska for which the drainage area State Planning Board (1941),by Condra(l920), is less than 300 square miles. The report and by Jenkins and others (1946), and was was prepared in the Lincoln office of the U.S. used by Furness (1955). FLOODS IN NEBRASKA ON SMALL DRAINAGE AREAS, MAGNITUDE AND FREQUENCY
SCALE IN MILES 20 10 0 20 40 60 I i I____|____|____|
Figure 1. Generalized areas of soil sources in Nebraska.
Loess silt is the predominant mantle of as deeply eroded canyons, and as rough broken Nebraska. It is wind transported from both areas. The soil varies widely intexture. The glacial deposits and mountain outwash and is drainage pattern is generally well defined and quite uniform in texture but decreases in runoff is prompt although the slope of each grain size toward the southeast. It erodes drainage basin is an influencing factor. readily when on a steep gradient and usually with a vertical cleavage line. Except for Residual soils, the least in areal extent scattered land-locked areas in the headwaters formed in place from sedimentary rocks and of streams draining relatively level areas of are found primarily in several smaller areas the south-central plains, the drainage pat of western Nebraska. The ground surface terns are connected and runoff is prompt. varies from nearly level to undulating, roll ing, rough and mountainous. Sedimentary The Sand Hill region, second in areal ex rocks are exposed in the rough badlands. The tent of the four major soil areas, is composed soil texture also has a wide range in the re mostly of porous dune sand formed from the sidual soil areas. The drainage pattern is weathering and reworking of sandy bedrock well defined and runoff is quite prompt. and early water and glacial deposits of sand and gravel. Except in the immediate vicinity Water-laid bottomland and areas of glacial of the few primary channels, there is no drift are exposed to a very limited extent in drainage pattern or surface connections to the State. the streams. Rainfall readily reaches the high ground-water table and forms numerous lakes and marshes. Sand Hill streams have CLIMATE a fairly uniform flow which originates from the ground-water table. Flood runoff is mi The climate of Nebraska is typical of large nor and comes primarily from the narrow interior continental areas in the middle lati strips of land immediately adjoining the tude; it is characterized by light average streams. annual precipitation, a great range of precip itation from season to season and year to The outwash mantle from the mountains to year, and frequent and abrupt changes in the west and northwest is found in several temperature and other weather conditions. areas along the western and northern parts of the State. The original high-plains surface The average annual rainfall shows a grad remains as a variety of topographic forms ual progressive increase from 14 inches in ranging from comparatively smooth to rolling, the extreme western part of the State to 34 INTRODUCTION inches in the southeastern corner. About 75 occur during the months April through Sep percent of the annual precipitation falls dur tember. There are some spring breakup ing the six-month period April through Sep floods; they occur most frequently in the Sand tember and about 42 percent of the annual Hill region where there is a relatively limited precipitation falls in May, June, and July. A range in discharge. large part of the summer rainfall occurs during thunderstorms and generally falls at Rainfall is the primary cause of floods. intense rates in short periods of time. Much of the rainfall results from thunder storms and ranges widely in amount, intensity^ and distribution, so that the relation of the DRAINAGE AREAS actual amount of rainfall to the flood peak cannot be correlated. Besides the stream The total drainage area of streams in a basins physiography which is fairly stable, major part of Nebraska does not contribute to the following conditions also influence the the surface runoff; therefore, it is necessary size of floods: (1) antecedent conditions, (2) to determine both the total drainage area and direction of the storm, (3) variation of soil the area which contributes to the stream by infiltration rate, and (4) land use and vegetal surface runoff. Both total and contributing cover. drainage areas are shown for the stations used; however, owing to the lack of complete coverage of good topographic maps of the FLOOD RECORDS AVAILABLE State, some of the drainage area figures are qualified as approximate. Some of the small Records for 5 or more years in length of drainage areas were determined from aerial- the annual floods not materially affected by survey photographs obtained from the U.S. regulation and diversion are available for Department of Agriculture, Commodity Sta 136 stations in Nebraska which have 300 bilization Service. square miles or less in contributing drainage area. In addition, six stations which have Nebraska is completely mapped by more than 300 square miles of contributing 1:250,000-scale maps of either 50-foot or drainage area are included because of their 100-foot contour intervals. The scale and strategic location. These six stations are: contour intervals do not permit reliable de White River at Crawford, Ponca Creek at termination of drainage areas, especially for Anoka, Plum Creek near Meadville, Long Pine smaller, fairly level areas or, differentiation Creek near Riverview, Bazile Creek near between contributing and noncontributing Niobrara and Wood River near Riverdale. drainage areas. Table 1 gives a list, in the downstream order, of the stations used, their drainage area size, Topographic maps, in scales varying from and a graphical illustration of the length of 1:24,000 to 1:125,000 and with contour inter record of annual peaks. Of the total of 142 vals varying from 5 to 20 feet, have been pub stations, 83 are crest-stage gages, most of lished for about two-thirds of the State. which are operated in cooperation with the Nebraska Department of Roads to define the annual peak discharge. Figure 2 shows the CAUSES OF FLOODS location of the 142 stations. The symbols on the map identify the type of station and the In Nebraska the annual floods on drainage number shown on the map corresponds to the areas of less than 300 square miles generally number preceding the station name in table 1. Table 1. Period of record of annual peaks at gaging stations
[Solid bar: Peak stage and (or) discharge. Open bar: Peak stage only] Drainage area Annual peak record, water years (square miles) No. Gaging station Contrib o m o m o m o Total co co Tf Tf in m to uting O) 0)0)0)0)0)0) I 1 T ( T 1 T ( I ( I ( I ( White River basin 4432 White River tributary near Glen ______7.97 7.97 J- 4437 Soldiers Creek near Crawf ord ______52.6 52.6 -\ 4440 White River at Crawford ______313 313 , N _^pr 4448 Chadron Creek near Chadron ______14.9 14.9 Ponca Creek basin 4535 Ponca Creek at Anoka ______410 410 wm Niobrara River basin 4563 Pebble Creek near Dunlap- ______-_-_---_-- 23.5 23.5 4564 Cottonwood Creek near Dunlap ______82.2 82.2 i 4577 Antelope Creek at Gordon ______-----_-- 61.1 61.1 ^i 4578 Antelope Creek tributary near Gordon ______-__---_ 26.6 26.6 4585 Bear Creek near Eli______360 78
4595 Snake River near Burge __-_-_-______620 100 4610 T\/Ti nno/"»Vi o fin rf o f'l^oolf Jji* \7"jjl oirfri Kif* 510 200 = __ 1 4625 Plum Creek near Meadville ______581 330 4635 Long Pine Creek near Riverview ______390 390 " m _ _ . Bazile Creek basin 4665 Bazile Creek near Niobrara ______440 440 Omaha Creek basin 6006 South Omaha Creek tributary near Walthill______2.64 2.64 6007 South Omaha C reek near Walthill ______15.1 15.1 = 6008 South Omaha Creek tributary 2 near Walthill ______1.51 1.51 6009 South Omaha Creek at Walthill______-_------.--_- 51.0 51.0 6010 170 170 ii a !920 (stage only) INTRODUCTION
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Map of Nebraska showing location of gaging stations used in flood -frequency analysis. FLOOD-FREQUENCY ANALYSIS average interval in which a flood of a certain magnitude has occurred once as an annual FLOOD FREQUENCY AT A GAGING STATION maximum. An objection to the use of annual flood is that the second highest flood in a VALUE given high year may outrank many annual floods. A regional frequency curve is considered to be superior to an individual station fre The partial-duration series is a list of all quency curve; however, an analysis must be floods above a selected base. The base is made at each gaging station before a regional generally selected as equal to the lowest an study can be started. nual flood so that at least one flood in each year is included. In the partial-duration se The flood history at a gaging station is a ries the recurrence interval is the average record of what has happened at that particular interval of time between floods of a given site during the specified period of observa magnitude. An objection to the use of the tion which is relatively short, statistically partial-duration series is that the floods speaking. Such a record is only a chance listed may not be fully independent events. sample of the flood potential representing the overall flood-frequency relation and as A definite relation exists between values in such may be a poor example for predicting the two series as shown by Langbein (1949) what will happen in the future, even at the and Chow (1950). The following table shows same site. comparative values of recurrence intervals derived by the two methods: TYPES OF SERIES Recurrence intervals in years There are two methods in general use for Annual flood series Partial-duration series studying -the frequency of floods: an annual 1.16 0.5 flood series and a partial-duration series. 1.58 1.0 2.00 1.45 2.54 2.0 An annual flood is defined as the greatest 2.52 5.0 momentary peak discharge in a water year 10.5 10 20.5 20 (October 1 to September 30). In the annual 50.5 50 flood array, the recurrence interval is the 100.5 100 10 FLOODS IN NEBRASKA ON SMALL DRAINAGE AREAS, MAGNITUDE AND FREQUENCY The annual flood series is used in this re erally it is confined to the maximum flood port. Where a frequency curve derived from during the memory of one or possibly sev the partial-duration series is desired, an eral individuals. Some of the stages noted annual-flood curve can be converted to the are beyond the limits of the defined stage - partial-duration series curve by the relation discharge relation, and a discharge could not expressed in the preceding table. be estimated. PLOTTING POSITION FITTING FREQUENCY CURVES The analysis of flood data starts with a After the flood discharges for each station listing of all the annual peaks at a gaging have been plotted against their computed re station. These are ranked according to mag currence intervals, a curve is drawn on the nitude starting with 1 as the highest. A time basis of the plotted points. The relatively scale must be computed, to obtain a plotting short length of most streamflow records and position for the frequency scale. There are the probable inaccuracies of small samplings several methods, but the one used by the Sur do not warrant analytical curve fitting. There - vey and in this report is fore, a visual best fit smooth curve is used in this report to average the points. It is known that the maximum flood or floods of record may have a recurrence interval con where siderably greater than the period of record. T is the recurrence interval in years, Therefore, in drawing a best fit smooth - n is the number of years of record, frequency curve, more weight is given to the m is the order of the mganitude of the-flood, lower floods than to the higher floods. Figure the highest being 1. 3 shows a plot of the frequency of annual floods for Plum Creek near Smithfield, Nebr. In the study of historical floods, n isthe num ber of years in which it is known that the flood was of the order assigned. LIMITATIONS OF A SINGLE STATION ANALYSIS Annual floods are plotted on a special form Generally the 2 5 -year or the 50 -year flood devised by Powell (1943) on which the dis is selected as the design flood. Table 1 shows charge is plotted on a linear scale as the that there are no gaging stations in Nebraska ordinate and the recurrence interval on a scale graduated on the basis of the theory of extreme values as the abscissa. 6000 HISTORICAL DATA 1000 Historical floods can be used to extend the frequency curve of a station to cover a longer period. Historical data, however, are usually LL O confined to stages or comparison of stages CD 3 above a high base and it is important to de O fine their order of magnitude with respect to -. 100 a period of time. Historical information on LU small streams is more difficult to obtain than on larger streams because the duration of the flood is quite short and the number of people affected is very limited. Care must be exer cised in assigning discharge values to his 10 I I I I I 1111 torical stages because of possible channel changes. RECURRENCE INTERVAL,IN YEARS Some information on historical floods was Figure 3. Frequency of annual floods, Plum Creek near obtained, usually from local residents. Gen- Smithfield, Nebr. FLOOD-FREQUENCY ANALYSIS 11 with less than a 300 square mile drainage bine the records for a number of stations, area which have 50 years of record of annual two requirements must be met. The first peaks and that there are only 5 stations condition is that all the records must be re which have more than 25 years of record of duced to a common time basis or base peri annual peaks. Of the total 142 stations, 113 od, and the second is that the stations must have only 10 years or less of record of annual have frequency graphs of the same general peaks. To define a 25-year or 50-year flood shape and slope, within limits of chance, so would require extensive extrapolation from that they may be considered homogeneous. the trend of the plotting position of lesser floods. The error of the curve could be con siderable at its outer extremity. BASE PERIOD The random manner in which flood events Table 1 shows graphically the length of are distributed with respect to time is an usable records at the 142 gaging stations. other limitation to frequency graphs based on Not all stations have records of the same records at a single station. length* If they are to be combined, records must be on the same time basis. The actual The maximum departure to be expected length of a short-period record of at least 5 between flood magnitudes or frequencies years' duration can be extended by correla computed from relatively short records and tion with the long-term record of a nearby their true (long-term) values increases with station. This correlation, however, is more the magnitude of the flood and decreases sensitive for small streams than for larger with the length of record {Benson, 1960). The streams and requires a long-term station in following table, based on Benson's study, the immediate vicinity. Therefore, because shows the length of record required at a there is such meager distribution of long- single site to define the frequency of floods term stations within the State,the base peri of various magnitudes with 10 and 25 percent od selected is 1947 59. Inasmuch as this of the true value 19 out of 20 times. base period is so short, it was also neces - sary to analyze records for 33 long-term Magnitude of flood, in recurrence Le"$th of record> in stations having drainage areas greater than intervals 10 percent 25 percent 300 square miles. This analysis was made for the period 1929 59 in order to establish 2.33-year. 40 12 10-year.... 90 18 the relation of the short base period to a 31- 25-year.... 105 31 year period. 50-year.... 110 39 The actual record at each station either Although the figures in the above table are included or was extended to the 13-year base based on a hypothetical study, they give an period, and for the 33 long-term stations indication of the possible errors, from chance mentioned above, to the 31-year period by alone, in frequency graphs based on short- computing a discharge figure for each year term records for a single station. A com of no record. These computed discharges, parison of the lengths of stream records which are based on correlation with records available in Nebraska on drainage areas of for long-term stations, are used only to as 300 square miles and less (table 1) with those sign the more nearly correct order numbers indicated by Benson (1960) suggests that very to annual peaks of record. few records in the State are long enough to define reliably the mean annual flood, and the floods of infrequent occurrence are less ac DEFINITION OF MEAN ANNUAL FLOOD curately defined. Analysis on a regional basis is used as a solution to the flood- According to the theory of extreme values frequency definition. as applied to floods by Gumbel (1945), the arithmetic mean of the annual peak dis charges in an infinitely long series is equal REGIONAL FLOOD-FREQUENCY ANALYSIS to the discharge corresponding to the 2.33- year recurrence interval. This definition is A flood-frequency curve based on a number generally accepted, and the 2.33-year flood of stations has greater reliability than a determined graphically is used as the mean curve from a single station. In order to com annual flood for this report. Annual-flood 12 FLOODS IN NEBRASKA ON SMALL DRAINAGE AREAS, MAGNITUDE AND FREQUENCY data for each of the individual gaging stations is the Sand Hills, and region A consists of were adjusted to the 13-year base period the remaining part of the State. There are (1947-59). 132 stations in region A and 10 stations in region B. HOMOGENEITY OF RECORDS COMPOSITE FREQUENCY CURVES The test for homogeneity of records in volves determining whether differences in In order to compare flood records at dif slopes of individual frequency curves are ferent gaging stations and combine them to greater than might occur by chance in ran define composite flood relations,it is neces dom sampling. This statistical test has a sary to convert the floods to a dimensionless 95-percent confidence level,that is, one sta basis. This was done by computing the ratio tion in 20 may plot outside the limits of the of floods of selected recurrence intervals to test graph. The slope of each individual sta the mean annual flood for each gaging station tion frequency curve is expressed by the in a homogeneous region. The median ratio ratio of the 10-year flood to the mean annual of each selected recurrence interval was flood. The average ratio derived from the then plotted against the corresponding re group was multiplied by the mean annual currence interval to give the composite fre flood for each individual station and the cor - quency curve for each homogeneous region responding recurrence interval was deter (fig. 5). mined from the station frequency graph. The recurrence interval thus obtained was then plotted against the effective length of record RELATIONS OF MEAN ANNUAL FLOOD in years on the specially designed test graph. The effective length of record is the number The composite frequency curves as de of annual floods of record plus one-half the rived in the preceding section define dimen number of estimated annual floods used to sionless ratios of the mean annual flood to complete the base period. floods of other recurrence intervals. In or der to define the flood-frequency curve in The test applied to the 142 gaging stations terms of discharge for a specific site, the used in this report indicates two homogeneous magnitude of the mean annual flood is re flood regions in Nebraska which are desig quired. The magnitude of the mean annual nated as regions A and B. The regional flood is obtained by relating it to measurable boundaries are shown in figure 4. Region B characteristics of the drainage basin. SCALE IN MILES 20 10 0 20 40 60 I i I____I____I Figure 4. Map of Nebraska showing flood-frequency regions and hydrologic areas. FLOOD-FREQUENCY ANALYSIS 13 1.01 10 20 30 40 50 RECURRENCE INTERVAL, IN YEARS Figure 5. Composite frequency curves of annual floods, regions A and S, period 1947-59. The physiographic factors which may in used to define a relation with the mean annual fluence the mean annual flood at a given point flood. Along with variations in mean flow, are size of the drainage basin, shape of the other factors or combination of factors that basin, alinement of the basin with the pre influence floods are not reflected in the size vailing direction of storm travel, channel of the basin, but their effect is related in storage, artificial or natural storage in lakes areas having somewhat similar physical fea or ponds, slope of stream, land slope, stream tures. Accordingly, the State was subdivided density, stream pattern, altitude, depth and into 10 hydrologic areas shown in figure 4. porosity of soil mantle, vegetal cover and Except for the boundaries of the regions A land use. Some of these factors are difficult and B which are also boundaries of hydrologic to evaluate and therefore cannot be used in a areas, the boundaries of the hydrologic areas correlation. follow the drainage divides or major streams. The mean flow of a stream is a hydrologic Records for the 33 long-term stations men measure that integrates all factors of runoff tioned under "Base Period" above were used and thus includes an indication of flood po in order to define mean annual flood relations tential. Because the majority of the station with respect to time. The graphical definition records used in this report are from crest- of the mean annual flood for the 31-year (1929 stage gages at which total runoff is not meas 59) base period was compared to the mean ured, the mean flow had to be determined annual flood defined by the 13-year (1947-59) from streams which have larger drainage base period at each of the 33 individual sta areas and which are not always strategically tions which are distributed around and within located. the State. This study revealed that the aver age correction factor required to adjust the The mean annual flood was correlated mean annual flood from the 13-year period to graphically with contributing drainage area, the 31-year period in the 10 hydrologic areas mean flow, stream slope, and shape of basin is as follows: factor. The drainage area size, the mean flow, and stream slope are all significant Area Correction factor factors, drainage area and mean flow being the most significant. The correlations, how 1 and 2...... 0.816 3 and 4...... 925 ever, do not give consistent results and inas 5, 8, 9, and 10. 1.00 much as mean flow was inadequately defined, 6 and 7...... 1.08 the contributing drainage area alone was 14 FLOODS IN NEBRASKA ON SMALL DRAINAGE AREAS, MAGNITUDE AND FREQUENCY The above adjustments are reasonably well flood with contributing drainage area for each established in all areas except in area 7 of the 10 hydrologic areas is shown in figure 6. where there is considerable spread in results for individual stations used to define the HYDROLOGIC AREAS average correction. Area 1, as shown in figure 4, is the north The mean annual flood for each station de east corner of the State. It includes all the termined from the 13-year period was cor smaller streams downstream from the Nio- rected by the average correction factor for brara River and upstream from the Platte the hydrologic area in which the station was River which are direct tributaries of the located. For each of the 10 hydrologic areas, Missouri River. It also includes the left the corrected mean annual flood for each bank tributaries of the Elkhorn River which station in that area was plotted against the are downstream from the Sand Hill area. The contributing drainage area for the station. area is generally quite hilly. The variation Curves were drawn to average all the data in of the mean annual flood with drainage area each area. The variation of mean annual is defined by 15 stations. 10,000 5000 O o UJ (O 2000 (T UJ CL I- 1000 UJ UJ u. o 500 CD z> o o 200 o o _J I 00 < z. z. Ul 2 0.3 0.5 12 5 10 20 50 100 200 500 CONTRIBUTING DRAINAGE AREA, IN SQUARE MILES Figure 6. Variation of mean annual Hood with contributing drainage area in hydrologic areas 1-10. FLOOD-FREQUENCY ANALYSIS 15 Area 2 is the southeast corner of the State. Area 5 (fig. 4) includes the small tributaries It includes Salt Creek, a tributary of the of the Platte River in the central part of the Platte River, and all direct tributaries of the State. The area contains some low rolling Missouri River in the State downstream from hills at the headwaters of the streams and at the Platte River. This area is also quite hilly the perimeter of the area but toward the in except for a flat area in Saunders County terior the land and stream slopes become which probably is the remains of an old less. As the drainage area increases, chan Platte River channel. The five Silver Creek nel storage becomes a factor in reduction of stations included in this report are in this the mean annual flood. Twenty-one stations flat area and their drainage areas include are used to define the variation of the mean many depressions which trap water and pre annual flood with drainage area. vent it from reaching the stream. Available topographic maps for this flat area do not Area 6 (fig. 4) includes the Medicine Creek distinguish between the contributing and the basin and all left-bank tributaries of the noncontributing area. Twenty-five stations Republican River between Medicine Creek are in area 2, but because the contributing and Harlan County Dam. This area is very drainage of the five Silver Creek stations is hilly and contributes to surface runoff, except not defined, the curve of variation of mean for the upper reaches of the Medicine Creek annual flood with drainage area is drawn on basin where part of the Sand Hills is located. the basis of the data from the 20 remaining Thirteen stations are used for defining the stations. The mean annual floods are higher variation of the mean annual flood with the than those in area 1 because of the greater drainage area. mean annual rainfall and resulting greater mean flow. Area 7 (fig. 4) is the western part of the State that includes drainage basins of the Area 3 (fig. 4) consists of the south-central Republican, South Platte, North Platte, Nio plains of the State. It contains the Big Blue brara, and White Rivers. This area has a River, the Little Blue River, and the tribu wide variety of topography and soils. Some taries of the Republican River downstream parts of the Republican River basin have de from Harlan County Dam. The headwaters of pressions and sandy areas which do not con these streams drain gentle sloping land, and tribute to surface runoff. Thirteen stations there are some depressions which trap run are used to define the relation of the mean off and prevent it from reaching the streams. annual flood to the contributing drainage Seventeen stations are used to define the area. The definition in area 7 is considered variation of the mean annual flood with drain to be the poorest in the State. age area. Area 8 is the southwestern part of the Sand Area 4 (fig. 4) includes Ponca Creek, the Hills as shown in figure 4; it is defined on tributaries of the lower part of the Niobrara the 'basis of only one station record. The River, the upper part of the Elkhorn River station frequency curve indicates that mean and all its right-bank tributaries, the Loup annual floods are considerably lower than River basin downstream from the Sand Hills, those defined in area 10. The relation of the and the left-bank tributaries of the Platte mean annual flood to contributing drainage River between the Loup River and the Elkhorn area is defined by the one station and the River. This area has a wide variety of topog slope of the relationship curve defined in raphy and soils. Flood flow at some of the area 10. stations is materially affected by the prox imity of the porous Sand Hills. Generally, it Area 9 (fig. 4) is the part of the Sand Hills is possible to determine the contributing north of the Niobrara River. As in area 8, drainage area if good topographic maps are only one station record is available. The available. Good topographic maps have not station frequency curve indicates that mean been made for this area; therefore, some of annual floods are considerably lower than the drainage areas are listed as approximate. those in area 10. The relationship curve, as Twenty-eight stations are used to define the shown in figure 6, is based on the one station variation of the mean annual flood with the record and the slope of the relationship curve contributing drainage area. The resulting defined for area 10. curve is so similar to that for area 3 that one curve is shown on figure 6 as representative Area 10 (fig. 4) contains the greater part of of both hydrologic areas. the Sand Hills which generally drain to the 16 FLOODS IN NEBRASKA ON SMALL DRAINAGE AREAS, MAGNITUDE AND FREQUENCY south and east. Only the area immediately It must be emphasized that the curves can adjacent to the streams contributes to surface not be extrapolated with confidence beyond runoff; the high base flow comes from ground the limits of the base data from which the water. The contributing drainage areas of the curves were derived. eight stations in this area are not very well defined and are listed as approximate. The range in size of the contributing drainage STAGE OF FLOOD DISCHARGE area is from 50 to 140 square miles. This report deals specifically with the fre - The definition of the mean annual flood with quency of flood discharges. Flood stage cor respect to contributing drainage area covers responding to these discharges may also be the range of drainage area from 1 to 300 of primary concern in the design of certain square miles in hydrologic areas 1 7. The structures and in other related studies. For range of drainage area defined in areas 8 10 rock-lined or firm-bedded streams at sites is from 50 to 200 square miles. not subject to variable backwater from down stream inflow or structures, a stage-discharge relation provides a ready solution to the prob APPLICATION OF REGIONAL FLOOD-FREQUENCY lem. For shifting-channel streams of Nebras DATA ka and where variable backwater may exist, the stage corresponding to the selected dis TRIBUTARY AREAS OF NATURAL RUNOFF charge may be approximated only after exten sive research. If the stage is to be investi This section gives step-by-step procedures gated, the engineer will find the site in ques for determining the magnitudes of floods in tion to be in one of two" categories: Nebraska having any recurrence interval up to 25 years at any site not subject to man- 1. Site at or near an established gaging made regulation or control that has a contri station. Gaging stations have been maintained buting drainage area between 1 and 300 square at several hundred sites in Nebraska. Loca miles in region A and between 50 and 200 tions of those established prior to September square miles in region B (fig. 4). 30, 1950, are described in reports of the Geological Survey (Water-Supply Papers 1309 1. Determine the total and contributing and 1310). Stations established since 1950 drainage areas at the site. The contributing are described in the annual series of water- drainage area is that part of the total basin supply papers entitled "Surface Water Supply area that contributes directly to surface run of the United States." A reasonable stage- off. discharge relation has been established at each of the small-area stations used for this 2. From figure 4, obtain the number of the report, and may be examined in the Lincoln hydrologic area and the flood region in which office of the Geological Survey. For sites at the site is located. or near gaging stations, it is usually possible to obtain stage data that are adequate for 3. With the contributing drainage area (step most purposes. 1) and the number of the hydrologic area (step 2), determine the mean annual flood for the 2. Site not near an established gaging sta site from figure 6. tion. The stage corresponding to a discharge of selected recurrence interval must gener 4. With the flood region (step 3) determine ally be obtained through the medium of a the ratio to the mean annual flood for the flood stage-discharge relation. The extent of the of the selected frequency of recurrence from investigation required to establish such a figure 5. relation will depend upon the accuracy re quirements. The following methods of de 5. Multiply the ratio of the selected flood riving a stage-discharge relation are noted to the mean annual flood (step 4) by the mean in decreasing order of reliability, (a) If the annual flood determined in step 3 to obtain need for data can be anticipated far enough in the flood magnitude at the site. If a complete advance, discharge measurements may be frequency graph is desired, repeat steps 4 obtained to define the relation up to the max and 5 for a number of recurrence intervals. imum discharge observed in the period. The MAXIMUM KNOWN FLOODS 17 relation may be extended by the application stage-discharge relation is indicated, and no of measured channel characteristics to ap discharge figure is shown for the maximum propriate hydraulic formulas. Shifting-chan stage. Some periods of known floods for the nel characteristics may be investigated by maximum stage are extended on the basis of studies of bed material and some long-term recovered floodmarks beyond the period of changes may be obtained from local residents. known floods for the maximum defined dis (b) If the need for data is immediate,the dis charge. For such periods, a leader line has charge for a past flood may be computed by been placed in the discharge column to indi hydraulic formulas if adequate floodmarks cate that the discharge for this known stage can be recovered and one point on the stage- could not be defined within allowable limits discharge relation curve thereby established. of accuracy. A leader line in other columns A direct measurement of discharge at the is also used to indicate that the information time of the visit will provide one other point. could not be determined. (c) A method has been used to develop ratings for stable channels from the product of the Twenty-five unusual peak discharges have stream slope at zero flow or low flow and been collected at miscellaneous sites or at characteristics of conveyance at a typical short-term gaging stations which have 300 cross section. This method is unsuited to square miles or less contributing drainage streams with unstable channel beds. area. These data are shown in table 3. The sites are listed in downstream order. Gaging stations having records of insufficient length MAXIMUM KNOWN FLOODS to be included in the flood-frequency analysis have been operated or are being operated at The design of major hydraulic^ structures numbered sites. Unnumbered sites are mis whose failure may cause loss of life should cellaneous sites where only one observation consider the maximum probable flood rather has been made. than one that may be expected to occur in a defined period of years. A prerequisite to As shown in figure 5, there is a great dif such an analysis is the record of maximum ference in the composite frequency curve for known floods. region A and for region B, and the curves of figure 6 show that the mean annual flood for Maximum known stages and discharges at a given drainage area can vary considerably the 142 gaging stations used in the flood- between hydrologic areas. A separate illus frequency analyses are shown in table 2. The tration was developed, therefore, for each of stations are listed in downstream order and the 10 hydrologic areas on which the 10- and the number preceding the station name cor 2 5-year recurrence interval floods are shown responds with the numbers shown in table 1 as a curve to compare with the maximum and figure 2. The flood region and hydrologic discharge at the stations and miscellaneous area in which the station is located is shown sites in that hydrologic area. The maximum as well as the total and contributing drainage discharge at the 142 stations used in this fre area. The contributing drainage area is used quency analysis are shown as open circles, to compute the peak discharge in cubic feet and the maximum discharge at the miscella per second per square mile. The period of neous sites and short-term gaging stations known floods is that for which the stage or which are listed in table 3 are shown as discharge is known to be the greatest. The closed circles. The gaging stations are iden stage is given for each maximum discharge tified by the last four or five digits of the except for stations 7730 and 7829. The dis index number, in order to correspond with charge at these two stations had been deter those shown in tables 2 and 3. mined from an indirect measurement prior to the establishment of the gage and there is no The relation of the maximum discharge to datum tie between the survey and the gage. the 10- and 25-year floods in the 10 hydrol Where the maximum stage and the maximum ogic regions are shown in figures 7 11. discharge are not concurrent, a change in the 18 FLOODS USLNEBRASKA ON SMALL DRAINAGE AREAS. MAGNITUDE AND FREQUENCY _ , . 00 O \ w CO <# t- rH CO C- O2 C- CO CM CO CM co in in c £J 'o * 3 O jvi C35 in CM CD" co ri(<" rH in O rH rH «?P rH *^ C^ CM CO « 3 S "G? § C Id 'O co 1o CM rH rH CO O CNJ CD CD CO in o m CD o c in cd 3 O T3 C! CO C35 C5 ^< CT C35 C5 C 3 OS- OS OS CO CO OS OS OS CO OS O m m T* if in in a13 in in in in in in in in m m if - 1 1 1 II co in rH a CO C5 C*3 CO rH CO CO CO O 00 CO 00 os in r- Q) O C*£ rO" ' m in co rj in r)< if3 ^< in in m ^< in ^ ^ ^ rt< m if C5 C35 C35 CT C5 C5 C15 OS OS OS OS OJ OS OS OS OS OS OS O _, X-- 1 c- cd CO o C5 CD 05 If3 CM rH CD r-4 i 1 r-l EH C- CM CO rt* 0 P3 CM rH CO CO o o o o c cd 'i -t-i -r-i in rH rH rH O0 CO CD CM C- o o co OS «; cu PR ofl *»3 CO TF rH CM CO CO rj W> CD Q Co £_i >^ t- cds 3§ -a C5 CD C5 if3 CM rH CO r o< -t-j C- CM CO Tt< O C» 3 CM rH CD O O O rH 0 C r? w r° in rH rH rH OJ CO CO CM CO CM rH CO OS r H « E-i CO TF CO co in in CO r 0 § -0 0 0 rt o c- c- c- J3 '£}) C -o ^ £ c- r(< c-- C- C- C- OS i i ^ ^ ^ T- £ to Omaha Creek basin 6B-6006 South Omaha Creek tributary near Al 2.64 2.64 1950-59 June 16, 1957 14.57 1,410 534 343 4.1 Walthill. 6007 South Omaha Creek near Walthill _. Al 15.1 15.1 1950-59 June 21, 1954 18.71 10,100 669 1,220 8.3 6008 South Omaha Creek tributary 2 near Al 1.51 1.51 1950-59 June 20, 1954 12.90 2,150 1,424 424 5.1 Walthill. 6009 South Omaha Creek at Walthill- ___. JTVAl JL 51.0 51.0 1951 59 June 13, 1957 24.92 14,200 278 1,470 9.7 6010 Omaha Creek at Homer ______Al 170 170 1920-59 June 4, 1940 a 32.5 1946-59 July 2, 1958 23.62 14,400 84.7 4,080 3.5 Tekamah Creek basin 6077 South Branch Tekamah Creek near Al 2.54 2.54 1950-59 July 15, 1950 21.3 a2,580 1,020 661 3.9 Craig. 6078 South Branch Tekamah Creek Al 4.08 4.08 1950-59 ,__do ___ ... 19.3 a l,800 441 694 2.6 tributary near Tekamah. 6079 South Branch Tekamah Creek near Al 9.73 9.73 1950-59 Apr. 21, 1954 20.17 3,130 322 1,060 3.0 Tekamah. 6080 Tolr Q TV* a h ("* Y» £*£*!** al" T t*lr HTYI a Vi Al 23.0 23.0 1950 59 July 15, 1950 14.26 4,400 191 2,190 2.0 Aug. 13, 1958 15.10 New York Creek basin 6086 New York Creek near Spiker- ______Al 1.75 1.75 1952 59 June 15, 1957 16.19 1,380 789 359 3.8 6087 New York Creek tributary near Al 1.55 1.55 1951-59 June 21, 1957 17.80 1,580 1,020 392 4.0 Spiker. 6088 New York Creek north of Spiker __. Al 6.50 6.50 1951-59 __ do _____ . 23.40 3,160 486 1,040 3.0 6089 New York Creek east of Spiker ___. Al 13.9 13.9 1950-59 July 2, 1951 24.14 6,020 433 1,320 4.6 6090 New York Creek at Herman______. Al 25.4 25.4 1944, June 11, 1944 e 20.8 1946-59, 1944, July 15, 1950 e !9.5 5,500 217 1,760 3.1 1946-59 Platte River basin 6840 Red Willow Creek near Bayard ___. A7 162 162 1932-59 May 10, 1942 7.8 July 3, 1956 7.33 2,320 14.3 1,260 1.8 6870 "Rin t* C~*Y*f*f*\£ n f^a T* T J^WP*! 1 t*Tn B8 267 80 1931 59 May 20, 1938 f4.46 8723 9.0 278 2.6 Dec. 21, 1945 *4.93 6920 Birdwood Creek near Hershey ____. BIO 286 80 1932-59 Dec. 15, 1940 5.12 Apr. 1, 1949 4.35 1,770 22.1 470 3.8 7671 South Fork Plum Creek tributary A5 9.81 9.81 1951-59 June 8, 1951 13.88 1,170 119 440 2.7 near Farnam. 7673 Plum Creek tributary at Farnam__. A5 19.8 19.8 1925-59 June 22, 1948 ^18.8 1951-59 June 8, 1951 13.36 2,070 105 150 13.8 See footnotes at end of table. 20 FLOCDDS IN NEBRASKA ON SMALL DRAINAGE AREAS, MAGNITUDE AND FREQUENCY _. , CO .0 .H g co IJj X M O5 CM oo in CM CO CO CO t- CO E-_ ^ rH CD CO CO CC cd Q cd 2 £ ^ i 1 rH CO CO 05 rt< in ^ < rH CM CM rH rH i 1 i-l in rf # a s (y Cd g g rH 1 g _, rH CM E- in oi <-H CO CM CM O O5 CO O1 & * 0) O* ,co t- 0 ,_, _, ^ ^ ^ E- O5 i-H CO CM in oo E- 00 COCO CM rH CO rH CM in 00 rl in cc 0) bo bo "5 oo cr (50 Cd 'jj CO E- rH CM CMCOCO O500CM in OOO CO rH OO O O5 rH rt< i i i M - 5M ° .S~ 4) 4) *! « E- rH E- E- E- 00 00 00 00 E- oo oo in E in rt< 00 OC ^ in ^i in ^ in inin in ^in in co^inin in ir O5 O5 O5 O5 O5 O5 OiO5 O5 O5O5 O5 OiO5 O5' O5 O5 O | rH ^-1 , 1 ^-1 T-l i i i O U g 0) H -a CM 00 CM CM CO O5 O5 CM O5 CM CM O CM CD E- 05" c x i 1 rH i 1 CM rH i 1 CM rH i-H rH i- cd Q CM CM CM CM rH pi> 0 O CO CO C ) 0) s^ ^D ^ < j ^ >>, T T 0) 0) CO t^> S d d d ^ d rH3 TI S *i £5 rH rH d d d rH r- r^ r^ K5 ^ ^D ^D r-j r-j r-j HD r-D >-D t-D r-j h, r-J £ O5 O5 O5 O5 O5 O5 O5 O5 O5 O5 00 O5 O5 O5 00 00 O5 O5 O5 O in in in in in in in in in if5 in in in in in in in in in if ° g3 »ll .(III 1 1 1 1 III I 1 -I-l SolS C-i-Hi-HE-rHCME-i-H i 1 rH rH E"- O5 i i i i i i in C- CM O CM O CM CV in in in ^ 4 rH in in in co rt< in in in in in if CU x >T[ O5O5O5O5O5O5O5O5 O5 O5 Oi C 5 O5 O5 O5 O5 O: CD CD CT> CD CD CD O . r> r* O rH 05 cd 'Jo # bo CO 00 CM CO rH CO if5 in O5 i-H O5 rH 00 O fd »iHfi od "£3^ CM i 1 hn U flj LJ rH O rH O5 pH '"J OO 00 CM 00 rH CO in 05 I-H O> rH 00 Cf "cd ji-L rt 00* 0) O5 in CM CM CO C*5 in rt< in rH CM CO rH O j-< ^ "S CO E- CM CO i-H Cl3 E- i-H CC rH CM rH C" - Q~ fn CM i i m in inm in in in inm ininin in inm in if ,3 't»0 J* T3 W) ^ § h [H t^ | rti & CO -o d rf d j> o t, i rt *O k> d O SM d *4) -^ "o "m O* 'S O . cd o ^ rH ^ J trnCOn^ ^IdL '' -i "£ cd n d c4 O "cd O?H Jj JCjMrHH MtM" MW ^D V. ucd F yocdrj CJ'sU cd> drjCM * '1 -iH -ad - i 1 i- 0) ^ ^' mrH CM co T(< ino i-HCMCo in E-OO 05 c ^ E- E- E-OO 00 00 00 O0 O5 O5 O5 O5 O) O O O C d CO U3 CO CO CO CO CO Cl3 CO CD CO CO C£> E- C- C- E- R E- E- E-E- E- E- E- E-E- t- t- C- E- E-E- t- E1 H CQ CO 7710 Wood River near River dale______A5 379 379 1946-59 June 22, 1947 19.75 20,000 52.8 710 28.2 7730 Dry Creek at Cairo ______A5 22.2 22.2 1949-53 June 6, 1949 1,100 46.6 570 1.9 1950 53 May 27, 1953 7.64 586 7750 Middle Loup River near Seneca __ BIO 1,140 60 1948-53 Jan. 7, 1949 2.61 Aug. 8, 1950 2.09 457 7.6 372 1.2 7755 Middle Loup River at Dunning ___ BIO 1,760 80 1946 59 Mar. 31, 1949 7.02 Sept. 13, 1958 3.90 830 10.4 670 1.2 7765 Dismal River at Dunning ______BIO 1,780 50 1946-59 Jan. 19, 1947 5.21 1932, May 26, 1952 3.18 996 19.9 564 1.8 1946-59 7777 Lillian Creek near Broken Bow __ A4 4.77 4.77 1947-59 June 22, 1947 e !2.2 930 195 74 12.6 7778 Lillian Creek tributary 2 near A4 2.04 2.04 1951-59 Aug. 12, 1951 e !2.4 585 287 37 15.8 Walworth. 7826 South Branch Mud Creek A4 .43 .43 1951-59 July 18, 1958 12.43 184 428 74 2.5 tributary near Broken Bow. 7827 South Branch Mud Creek at A4 400 45.9 1948-59 June 17, 1956 16.41 1,790 39.0 74 24.2 Broken Bow. 7828 North Branch Mud Creek at A4 15.5 10.8 1951-59 __ do _____ . 16.16 1,550 144 194 8.0 Broken Bow. 7829 Mud Creek tributary near A4 5.98 5.98 1945, May 27, 1945 1,500 251 74 20.3 Broken Bow. 1951-59 1951-59 July 21, 1951 e !4.80 870 7830 Mud Creek near Broken Bow_____ A4 440 81.1 1949-56 June 17, 1956 9.48 600 7.4 416 1.4 7843 Oak Creek near Loup City ______A4 41.9 41.9 1950-59 July 3, 1951 e !5.50 1,420 33.9 601 2.4 7845 Oak Creek near Dannebrog ______A4 122 122 e !9.0 1950-57 June 17, 1954 17.23 1,880 15.4 1,210 1.6 7847 Turkey Creek near Farwell _____ A4 27.2 27.2 1950, July 9, 1950 e !7.50 1,600 58.8 1,180 1.4 1953-59 7855 North Loup River at Brewster ___ BIO 1,890 140 1946-51 Feb. 2 5,2 6, 1950 4.20 June 14, 1951 b 3.40 a l,600 11.4 840 1.9 7860 North Loup River at Taylor _____ BIO 2,210 180 1937-59 _._do _____ . 6.50 g 2,830 15.7 1,400 2.0 Feb. 25, 1957 e 9.5 7875 Calamus River near Burwell ____ BIO 1,260 110 1941 59 Mar. 19, 1950 5.19 May 16, 1951 3.76 1,060 9.6 558 1.9 7891 Davis Creek tributary near A4 2.29 2.29 1951-59 July 3, 1951 17.74 a906 396 324 2.8 North Loup. 7892 Davis Creek tributary 2 near A4 6.79 6.79 1951-59 July 14, 1957 16.82 722 106 194 3.7 North Loup. 7893 Davis Creek near North Loup____ A4 21.1 21.1 1951-59 __ do _____ . 15.68 1,820 86.3 695 2.7 7894 Davis Creek southwest of North A4 41.6 41.6 e 21.5 T .r\tnr\ 1951-59 June 16, 1957 19.35 2,220 53.4 1,040 2.1 See footnotes at end of table. 22 FLOODS IN NEBRASKA ON SMALL DRAINAGE AREAS, MAGNITUDE AND FREQUENCY 0 ^ J, g 8 t-t CM r^ t-t OOOO COLO OCO CO COOSLO LOLOWCO OS £ g 0 g| s3 *0 Q!CM CM CM CO t t CO CO CO Tt* ^ LO rH CO CO CM Tt* Tt^ CO CO OS £ ,* r-t CO *-? LO o o CM OCM OO OCO CO *# O <# OOOO O O d flj rj-j orj ^CQ O CO O O t-tOS COCO OSrP O COt-tCM CDCOr-HO C" CO CD CM CM rJiLO CMCO r^CD -^ C"lOCM OOCOCOC" LO "^ d § f2 N' r! t t t t CM t t C"» CM CM * I CM Tt* CO cC **"* O* " rH M CO O O 3OS COO ^fO COCM LO COOS O COCMOCO CM C- * CM C--t- LOlO C"CM C"COCM OS OSCOOOS CDrHCMCO CM CU tUO OJO <1> CM CO C- CfJT-I rPC- t-tO »-( T-( C» C- OSOSCOCO O<-HOOCM CO tuo rt -rj cu T-H T-H t-t r- IT-I CM T-ICM CMCMft) CMT-I COCOi-HCM CM £ o jn£i rt co m co o3OS COc- OO C-OC- CO COCOOt-t T-HOS.-H OS LO Tjl LO Lf SLO LOrJI LOLO Tj 1 CV5 CM CM --H O LO OS CC5 <-H C- CO CM OS C- rt 'co 5 bD , 1> rH d TP OS CO C- LOO OCM O O t-t LO ^ LO COCO CM rH r-t 4J -rH OS t-t CO COLOOCMC-OS C~ t-t TjtC- 08 os t-t t-t t-t C^ t-t t-t N hn flj U Cti y^ crS CM CM t-t O LO OS Ci 3 t-t C- CO CM OS C- "tf OS CO I> LO^t-tCMOOt-tLO^ LOCOCOCM OS r-1 CO COOSrTJCMC~CM C- t-t ^ C- t-tC-'COt-tCMCO t-t CM "S § ~ o o «« 1 ^^ TJ^ Tjl TJ^ Tjf ^^ OJ OJ OJ OJ OJ OJ OJ OJ O .« T3 ^ .rH d) CM ' co1 _0) _Q . 1O rn isCu W* rfS 2 8T: i "*3 isCreekCotesfield____near SpringBranchCreekstnear uD^l) JH ^ ,H CO CDG^JOJ o rH BranchSpringCreek3tat . A ^ -4-* f-i H t> 0 (D ^CQ^ * CQ I-H "^ " " .J-i ri c1 ^ ^ (U ^ rrt PlattebasinRiyerContinued 5 J3 rt Q^ Cti ,3 ^yj trj* "^J j^" j^ ^ j^ ^ s rlW/~vTKo,-»Vi"ir'aT>QQlj-^t CO tuo d * ^H 1'H *^ ^^ ? 1 . > ,1 Cu J3 Q M Q '7*1 rH tuoco1 o rayton. folbach. ) U(^r^ -^ U ^?H JH^ Odoo).a).a)Uorrpo ° ° ° r^ fl* o ^ un r^oUo d .^ g 6 « S t? S Q^ t5 3' coU PQco co co co co cot^ & Qp5 ^ t~ 0) LO C- CO OS THLO LOO LO O LO LO OLO CO C-OS O, os o o c) T-Ht-» COLO LO 00 T-H CM COCO CO COCO rj( CO OS OS Os osos osos os os o o oo o oo o 1 c- c- c- c- C-C- C- C- C- C- CO CO COCO CO COCO CO ffl CO 8041 Silver Creek near Cedar Bluffs __ A2 10.9 1894- ___do ______15.02 4,040 653 6.2 1959 8042 Silver Creek near Colon ______A2 29.9 1894- 19.22 12,000 1,320 9.1 1959 8043 Silver Creek tributary near A2 14.3 1894- __ do ______17.32 5,000 261 19.2 Colon. 1959 8044 Silver Creek tributary at Colon __ A2 22.4 1894- __ do______19.29 4,640 351 13.2 1959 8045 Silver Creek at Ithaca. ______A2 72 1894 __ do ______16.92 21,600 816 26.5 1959 Weeping Water Creek basin 8064 Weeping Water Creek at Elmwood A2 21.4 21.4 1950-59 May 9, 1950 e24.6 7,600 355 2,640 2.9 8064.2 Stove Creek near Elmwood ______A2 4.94 4.94 1950-59 __ do ___ __ e !8.2 5,370 1,087 2,020 2.7 8064.4 Stove Creek at Elmwood ______A2 10.0 10.0 1950-59 __ do______e23.0 9,500 950 2,010 4.7 8064.6 Weeping Water Creek at Weeping A2 75.5 75.5 1882- __ do______e !8.5 30,300 401 3,920 7.7 Water. 1959 8064.7 Weeping Water Creek tributary A2 1.07 1.07 1950-59 May 15, 1954 18.02 1,160 1,084 416 2.8 near Weeping Water. 8065 Weeping Water Creek at Union. __ A2 238 238 1947-59 May 9, 1950 J26.80 60,300 253 4,900 12.3 Little Nemaha River basin 8101 Hooper Creek tributary near A2 7.81 7.81 1950-59 June 1, 1951 16.55 3,090 396 1,140 2.7 Palmyra. 8102 Hooper Creek near Palmyra. ____ A2 57.5 57.5 1950 59 May 9, 1950 e23.0 47,600 828 4,490 10.6 8103 Owl Creek near Syracuse ______A2 25.4 25.4 1950 59 do e 30.6 a !6,000 630 2,860 5.6 8104 Little Nemaha River tributary A2 .76 .76 1950-59 do _ _ _ _ e !6.6 1,280 1,684 465 2.8 near Syracuse. 8105 Little Nemaha River near A2 218 218 1950-59 e 36.7 225,000 1,032 12,200 18.4 Syracuse. Nemaha River basin 8155 Muddy Creek at Verdon ______A2 188 188 1953-59 July 10, 1958 31.50 31,900 170 9,470 3.4 Kansas River basin 8230 North Fork Republican River at A7 320 130 1931-59 Apr. 28, 1947 5.92 2,110 16.2 611 3.5 Colo. Nebr. State line. 8235 Buffalo Creek near Haigler ______A7 180 21 1941-59 June 27, 1948 4.37 a !40 6.7 38 3.6 Mar. 25, 1957 5.36 8240 Rock Creek at Parks ______A7 180 14 1941-59 Sept. 3, 1951 3.80 95 6.8 43 2.2 Jan. 26, 1949 3.92 8360 Blackwood Creek near Culbertson A 7 290 290 1946-59 June 17, 1955 ( 14.64 1,650 5.7 648 2.5 CO CO See footnotes at end of table. 24 FLOODS IN NEBRASKA ON SMALL DRAINAGE AREAS, MAGNITUDE AND FREQUENCY CO o r-l CO CO r-l J. a 00 O O O 10 O C£) t- 00 CO CD t-OOCM COCM rH 00 Is- rt c CD TP O t- rH CO nf * CM T}< C- m CMCMCM rHCO -^ CM CO o' rH a a rH CM rH CM CO '-> -J< CO -J< O CM CM n 1 -)* rH 00 O CO o-^o oooo t~- -tf m Station annual o rH O CD OS t- CD If5 os m c- -»< ooso t~-os o CM if> CM*^ t- OS t CD m CMCO -^ co in o co co oo CM"m os rH nfi m m s o CM rH cy'43 OS -J< OS ^ t oosm osrH m co m 3.. , CD in rH CD CM rH rH * " 1 00 O CO O 00 ocoo -Ft- os m CM DJO CM oo m c- os c- If5 00 CD OS COrHC- m-^ CM CD CM CD t( rH CD OS OS CD * "< bjo $H 3 m rH rt C s rt O O O O O O CO 5 O O o o o ooo oo o t- o CO CM CM CD O O 00 OC5 rH CD a 4-> o 10 rH m c 0} ^^ ^^ t " rH rH rH O CN CD o ^ o !O m rt CM CM CN r- 1 CM rH CN CO CM (M CM CN rH CM CVI rH rH rt 3 c c O O >> ® a >> a CU i * CU ^ * CU 'C ^ "j*"- ^_ r~* p rH /-, 1 o W) r1 rt £ M >-H M h-M P^P »H g 'Z ;_ IS £ leH " p. ^ " 3 CU 3 CU ^ 3 \& 1^ S Hj r- & *-. H-5 CO *-5 CO -D 0 OS OS OS OS OS OS o S OS OS OC) 00 00 os a OJCOCD CDOS OS OS OS o floods m m m m m m If5 m m ir m m m ir minm min m m m rH3 *o known III III 1 ! 1 1 1 rH CM CM CD (M (M CN 1 rH rH C- rH C- OC» os o tr rHOOOO OOCO CO CO CO m m m o m m If5 m m -tfi in -J< OC io m -j m-fiT}< -) * C 2-0 o rt o . r-4 (U CD CD CD CD CD CD u3 CD CD CC) CD CC) CC OO CO CO CO OO CO CO o ojo d T3 rH CD rt <[J < CM _0 CU CU CD 8520 Elm Creek at Amboy__«/ ______A3 39.2 39.2 1948-53 Sept. 20, 1950 9.45 3,860 98.5 964 4.0 8807.1 School Creek tributary near A3 13.1 13.1 1952-59 Sept. 6, 1958 12.14 164 12.5 104 1.6 Harvard. 8807.2 School Creek near Harvard _____ A3 55.1 55.1 1953-59 July 10, 1958 16.74 960 17.4 440 2.2 8807.3 School Creek tributary 2 near A3 14.0 14.0 1953-59 ___do ______16.17 510 36.4 213 2.4 Harvard. 8807.4 School Creek near Saronville ____ A3 89.4 89.4 1952-59 July 14, 1952 e !7.6 1,280 14.3 888 1.4 8836 South Fork Big Sandy Creek A3 15.2 15.2 1953-59 Aug. 16, 1957 13.56 595 39.1 185 3.2 near Edgar. 8837 South Fork Big Sandy Creek A3 32.0 32.0 1950, July 9, 1950 h !7.3 a 1,400 43.8 352 4.0 TI &z\ T* yinfr-^TTT-OYH" 1952-59 8838 South Fork Big Sandy Creek A3 49.4 49.4 1952-59 July 14, 1952 e !6.4 1,740 35.2 629 2.8 near Carleton. 8839 South Fork Big Sandy Creek A3 81.9 81.9 1952-59 June 27, 1952 e21.8 3,160 38.6 1,520 2.1 near Hebron. a App r oximat e. From information by local residents. b Maximum observed. ^ Present site and datum. cApproximate natural peak. k Exceeded by flood of Apr. 24, 1935. dRegulated peak; affected by backwater. mAt site 2-3/4 miles upstream, from slope-area measurement. eFrom floodmark. n One of the greatest floods known occurred June 22, 1947; Datum then in use. stage and discharge unknown. sAdjusted for diversion. to tn 26 FLOODS IN NEBRASKA ON SMALL DRAINAGE AREAS, MAGNITUDE AND FREQUENCY m £ w E-* ft rt PH O i I in oo in CD ^^ ^* in 00 T i CD 00 O CN t- E- ^ 'So d -o 'So 2 5 35^3 t:o < < -e " JH X! "^ t/J a i s A i ' 0) V} !^> CD W o > S center sec. 6,T. 9N.,R.2 W. N Furnished by Corps of Engineers. bApproximate. 28 FLOODS IN NEBRASKA ON SMALL DRAINAGE AREAS, MAGNITUDE AND FREQUENCY 80 I I 1 1 1 1 1 4665^ - 50 O z o - 0 UJ to Or 20 ^ UJ d^^ 0_ .6009 x Area 1 X^60IO°t^o H ^ UJ UJ |0 6007 -^& u. '^VI&" o - CD O 6069 x^6090^ _ t 5 ^6060 EXPLANATION - 607^^ UJ /^6086 C o _ o 0 6077^x' Gaging station or 6006Q Miscellaneous site X 2 O ^ SOTO^' en 6O67n^ 0 ^^Hooe 1 ^ 0.7 1 1 1 1 1 1 1 1 ~ 2 5 10 20 50 100 200 50 300 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 6105 O 200 EXPLANATION o Gaging station 100 O Miscellaneous site or short- Z term gaging station eo3o0 0 o o 6065 Ul 50 °e.o2 8040^ or 6064.6 6I55Q Ul Area 2 O 0. i- 6045 uj 20 O x UJ u. 08I03 0 6042 ., / ^ 8O38° O ^^ 6OIS 0.5 < *035.7 1 1 1 O i 1 1 1 1 1 1 1 1 1 0.3 0.5 2 5 10 20 50 100 200 30 CONTRIBUTING DRAINAGE AREA,IN SQUARE MILES Figure 7. Relation of maximum discharge to 10 and 25-year floods, region A, areas 1 and 2. MAXIMUM KNOWN FLOODS 29 30,000 20,000 Area 3 ,6515 10,000 5000 6520, cr MS9 LU O O. 3510 id 2000 UJ 6500 Lu 6837; 65° O 6502. 6607.4 CD 1000 '6807.2 HB5I3 O 500 8807.3 EXPLANATION o Gaging station Miscellan tous site 200 100 50 0.40.5 10 20 100 200 500 30,000 20,000 10,000 5000 2000 1000 500 EXPLANATION o Gaging station 200 Miscellaneous site or short term gaging station 100 0.30.40.5 12 5 10 20 50 100 200 500 CONTRIBUTING DRAINAGE AREAJN SQUARE MILES Figure 8. Relation of maximum discharge to 10 and 25-year floods, region A, areas 3 and 4. 30 FLOODS IN NEBRASKA ON SMALL DRAINAGE AREAS, MAGNITUDE AND FREQUENCY 100 0.5 20 50 100 200 500 100,000 -j-j \ \ 1 1 1 1 \ I O 8395 50,000 EXPLANATION o Gaging station 0 z o Miscelkineous site or short °8405 o term gaging station 20,000 10,000 O m 5000 o z 2000 1000 500 300 2 5 10 20 50 100 200 400 CONTRIBUTING DRAINAGE AREA,IN SQUARE MILES Figure 9. Relation of maximum discharge to 10 and 25-year floods, region A, areas 5 and 6. MAXIMUM KNOWN FLOODS 31 50,000 i r I I IT 8375 _ 4564, 20,000 10,000 5000 O .4437 O LJ CO .4433 or UJ O '6840 4440 CL 2000 -e h- 4562 4578 LU O o 8360 LU 4448 - 1000 o z 500 UJ o 4577 QC 4432. I O CO 200 ^8235 EXPLANATION 100 O 8240 Gaging station Short-term gaging station 50 20 I I 2 5 10 20 50 100 200 4OO CONTRIBUTING DRAINAGE AREA, IN SQUARE MILES Figure 10. Relation of maximum discharge to 10 and 25-year floods, region A, area 7. 32 FLOODS IN NEBRASKA ON SMALL DRAINAGE AREAS, MAGNITUDE AND FREQUENCY I III SUMMARY The accuracy of flood magnitudes for se 1000 lected recurrence intervals obtained by meth - - 6870 oo^X ods outlined in this report is contingent upon * INT.DUP..D.C.62- 3551X;^ - ISCHARGE,IN»CU C0(Ji 8064.2( 8032 ^ '-X8043^x V^ O 6044 ^3037° ^ ^8041 8013.2 e*P .sv 0 8034 - "Ws.-X8IOI X> *8O33 $K" 6OI2* 8104^ 3x^6-*^^ <^&XA% 1 -