Survey Report Appendices
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1961 lS FIgFIv S3310N3ddV Vl N~IO_-117VO AINnO3 IO-108BNH )133~13 O00MCl3~I s3soaana 03177v ONV 70~INOO (]007_-I s~ ~0.-I 1~10d3~1 13AWnS ..... G’~..... ON 7VI~39 APPENDIX A HYDROLOGY TABLE OF CONTENTS 3 Paragraph Title 5 5 SECTION I - GENERAL A-1 3 A-1 PURPOSE AND SCOPE A-I A-2 PLAN OF IMPROVEMERT A-I SECTION II - BASIN CHARA6"fERISTICS A-I A-3 LOCATION A-I A-4 TOPOGRAPHY A-I A-5 TRIBUTARIES A-2 SECTION III - CLIMATOLOGY A-2 ~S A-2 PRECIPITATION A-2 SECTION IV - STORM ANALYSES A-3 A-8 MAJOR STORMS A-3 A-9 STANDARD PROJECT STORM A-3 a. Definition A-3 b. Storm transposition A-3 A-10 PROBABLE MAXIMUM STORM A-4 SECTION V- STREAMFLOW AND FLOOD ANALYSES .A-5 A-II STREAM-GAGINGSTATIONS AND RECORDS A-5 A-12 MAJOR FLOODS A-5 A-13 HYIROGRAPH DERIVATION A-6 A-14 STARDARD PROJECT FLOOD A-6 a. Definition A-6 b. Snowmelt A-6 c. Hydrograph determination A-7 A-i Table of Contents (cont’d) Title P/ZERVOIRS A-7 SECTION VI - FREQUENCY ANALYSES A-8 A-16 DISCHARGE-FREQUENCYANALYSES A-8 A-17 RAINFAI~ DEI~I~-DURATION-FREQUENCYANALYSIS A-8 SECTION VII - INTERIOR I~AINAGE A-8 A-18 PROBLEM AREA A-8 A-19 DESIGN CRITERIA A-9 TABLES Nt~n~er A-I Precipitationstations in or near Redwood Creek Basin A-2 Major storms of record A-3 Stream-gagingstations A-4 Annual maximum discharge, Redwood Creek at Orick and Smith River near Crescent City A-5 Unit hyd~ograph data PLATES l~er A-I General map of basin A-2 Area - Elevation curves A-3 Normal annual precipitation A-4 Mass curves and isohyetal map, 18-20 January 1953 A-5 Mass curves and ~sohyetal map, 17-23 December 1955 A-6 Hydrologic data and unit hydrograph derivation, 20-25 December 1955 A-7 Hy~ologic data, 29 December 1954 - 2 January 1955 A-8 Hydrologic data, standard project storm-flood A-9 Discharge frequency curves A-IO Rainfall Depth-D~ratiom-Frequencycurves A-ii HYDROLOGY P E SECTION ! - GENERAL A A-1. PURPOSE AND SCOPE D E This appendix presents climatic and hydrologic d~ta for Redwood R O Creek Basin, California. It includes derivation of the standazd project flood as a basis for the design of local protective works, and develop- 3 5 ment of a dlscharge-frequencycurve used in the economic eval~tion of 5 the project. This appendix was approved by the Chief of Engineers by 5 2d Indorsement dated 2 ~rch 1960, to letter SPNGP~ dated 24 December 1959, Subject: Report on Standard Project Flood and Discharge Frequency Analysis, Redwood Creek Basin, Humboldt County, California. A-2. PLAN OF IMPROVEMENT The plan of improvementas presented in detail in the main report consists of channel improvementsalong the lower four miles of RegwOod Creek. The work would consist of channel rectification,levees and partial revetment. A trapezoidal~typechannel would be used through the urban and downstream rural areas and a system of setback levees with improved channel upstream from the mouth of Prairie Creek° SECTION IX - BAS~ CHARAC~TICS A-3. L~ATION Redwood Creek located between 40°40’ and 41°30’ north latitude, drains an area of 283 square miles along the northern California coast. The basin is situated entirely within Humboldt County and flows directly into the Pacific Ocean at a point 50 miles south of the Oregon-California border° Orick, the only town in the basin, is located about three miles upstream from the mouth of ~dwood Creek and immediately downstream from Prairie Creek. A general map of the basin and locality is shown on Plate A-1. A~. ~P~RAPHY The basin consists of an elongated, mountainous,heavily wooded area which extends 56 miles along a northwest-southeastaxis with a maximum width of about seven miles. The elevation of the basin bounde~ies vary from sea level at the mouth to about 5~400 feet mos~lo at :the southeastern extremity of the basin. The most remote part of the basin lies 30 miles inland from the Pacific Ocean ~ud h~ an average windward barrier height of 2,500 feet and average leeward height of 3,500 feet. The area-elevatlon curve, shown on Plate A~2, indicates that approximately50 percent of the basin area lles above elevation 2,000 feet m.s.l° and five percent above elevation 4,000 feet m.s.l. In the lower four-mile reach, Redwood Creek has a fairly uniform slope of about eight feet per mile. The main stream has a watercourse length of about 64 miles. The only significant area of level land is located along the lower reaches of Redwood and Prairie Creeks. A-5. TRIBUTAR7~ The long, narrow shape of Redwood Creek basin limits the size of 5most tributaries to about equal length and drainage area. Prairie Creek the only major tributary, has a stream length of about 12 miles, drains an area of about 40 square miles and joins Redwood Creek near river mile 3.5. SECTION III - CLIMATOLOGY A-6. TEMPERATURES The lower coastal part of the basin is characterizedby mild, dry summers with frequent local fog and mild, wet winters. Temperatures recorded at Orlck-PralrieCreek Park are representativeof the lower part of the basin. This station has registered a high of 95 degrees Fahrenheit a low of 19°F., and has an average annual temperature of 51.9°F. The inland portion of the basin has little summer fog and a greater diurnal temperature range than 0rick. Temperaturesrecorded at Forest Glen, located on South Fork Trinity River about 52 miles south- east of Eureka, are representativeof inland areas. This station has an average annual temperatureof 51°F., a high of 105°F. t and low of -2°F. A-7. PRECIPIT~ON There are two U. S. Weather Bureau precipitationstations within the basin. Orick-Prairie Creek Park has been in operation since 1937 and Blue Lake Redwood Creek since 1956. There are eight active U. S. Weather Bureau stations in or near the basin and 13 known private stations for which sufficient records are available to estimate normal annual precipi- tation. Station data are presented in Table A-1. Locations of hydrologic stations ar~ plotted on the Normal Annual Precipitationmap on Plate A-3. Generally, only ten or twelve official and private stations are available for construction of storm isohyetal maps. Basin orientation and topography exert a strong influence on areal distributionof precipitationan~ the pattern of normal annual isohyets is used as a guide in constructionof storm isohyetal maps. Ninety percent of the seasonal precipitationgener- ally occurs during the period, October through April, with monthly distri- bution as follows: Normal Monthly Precipitationin Percent of Seasonal Total Jul Au~ Sep Oct Nov Dec Jan Feb Yet Apr May Jun Total 0.7 0.4 1.5 9.7 12.9 16.7 14.3 14.7 13.6 7.2 5.9 2.4 lO0 A-2 The basin normal annual precipitationis estimated to be about 80 inches, _varying from 70 inches at the lower portion of the basin to over 85 inches across the central portion. The high seasonal total compared to coastal basins further south is due to more frequent preclpitationoccur- rencesratherthan to rainfall intensity. The 3-day rainfall value which can be expected to occur on the average of one year in ten is about ten inches, which is not significantlyhigher than values for the central and southern coastal areas of the State having normal annual precipitationof 30 to 40 inches. Precipitationin excess of 0.Ol~inch cam be expected to occur on the average of 120 days each year. Snowfall occurs at the higher 3 elevations but Is of relative minor importance since less than five percent 5 of the basin lies above elevation 4jO00 ~s.lo (the elevation above which 5 snowfall is significant)°Average annual snowfall at elevation 2,500 m.s.1. 7 is estimated to be about 50 inches and at 4,500 m.s.1, about lO0 inches. Snow cover seldom lasts very long or attains more than a foot or two in depth. SECTION IV - STORM ANALYSES A’8. MAJOR STORMS Flood-producingrainstorms in this area result from the passage of one or more extratropical cyclones. These storms cause precipitationover large areas generally exceeding lO,O00 square miles. Most major storms occur during the period between November and April° The storms of October 1950 and November 1926 were exceptions. Although storms sometimes persist for five to ten days, the flood producing portions generally occur within a three-day period. Rainfall records show that notable storms occ~uu~d during February 1915, October 1950, January 1953 and December 1955. Isohyetal maps and mass curves at selected stations are presented on Plates A-4 and A-5 for the January 1953 and December 1955 storms. A +~bulation of daily rainfall at representativestations for the ten largest storms of record is presented in Table A-2. A-9. STANDARDPROJECT STORM a. Definition. The standard project storm is define~ as the most critical storm of record within a region meteorologicallyhomogeneous to the basin under study, or the most critical storm of record in adjacent regions that can be reliably transposed to the subject basin. The transposition boundaries are limited only by the reliability of methods used to accomplish the transposition. b. Storm transposition. General-type storms are more critical than the local-type over basins the size of Redwood Creek or over basins receiving high annual precipitation°The major storms, cited in paragraph A-8, were studied to determine which would be most critical when transposed over the Redwood Creek basin.