|
<br />the watershed. The snowfall is heavy in the mountainous headwater
<br />region and decreases in amount toward the mouth of the river. Ap-
<br />proximately ollO,half of the average annual preeipitation at North
<br />Lake occurs as snowfall, and only about 15 percent of the average
<br />annual preeipitation at Las Animas is in the form of snew. The aver-
<br />age annual snowfall varies from about 19 inehes at Las Animas, eleva-
<br />tion 3,899 feet, to amounts exceeding the approximate average annual
<br />of 115 inehes recorded at North Lake, eleva,tion 8,800 feet. The one
<br />snow course in the drainage basin is located 'on Whiskey Creek, a
<br />tributary of North Fm'k, in the headwater area. The average snow
<br />on the ground, April 1, for the 3'year period of reeord, was 27.5 inehes.
<br />The average snow-cover measurements on April 1 for the period of
<br />record, 1941 and 19,42, are given in table No, 5, appendix B.'
<br />26. Meteorological characteristics.-The major topographic features
<br />lying between affeeted areas in New Mexico and southern Colorado
<br />and the souree region of ail' masses produeing precipitation, indicate
<br />that the general effects of these topographieal features upon the
<br />invading ail' masses is the eritieal factor in regulating major precipita-
<br />tion therein. Studies of these features dealing with the general
<br />meteorology of the region are diseussed in appendix B.' Analyses of
<br />rainfall records ,in Colorado and New Mexieo indicate that poly-
<br />morphous stormsoeeur within the Purgatoire River Basin, and that
<br />large magnitude storms usually occUr during the period from April
<br />through October, Tbe general storm, of which two types occur, and
<br />, the thunderstorm (local summerstorm) produce consummated precipi-
<br />tation.
<br />27. Onc of the general storms is identificd as the stable wave or
<br />partly oeoluded type. These storms covel' comparatively lar!,:" areas,
<br />mtcnsitics are usually low, and being frontal, show the effects of
<br />oro!,:raphic influence. The storm'periods may cover several days.
<br />28. The other general storm may cover large areas, but owing to the
<br />nature of the storm type, a front aloft, precipitation should not be
<br />influenced by orographIc effects. Further, the exact location of the
<br />precipitation area is a random affair depending upon the rates of
<br />movement and the intensities of the ail' masses involved. These
<br />storms rilaY persist for periods'in excess of 24 hours, but are usually of
<br />shorter duration. Intensities may be comparatively high at several
<br />locations within the general storm area, tending to indicate a series of
<br />local thunderstorms.
<br />29. The local summer storm represents a form of penetrative con-
<br />vection due to insolational heating of the lower layers of the atmosphere
<br />and orographic influences. These storms are of short duration
<br />, intensities are relatively high, and they covel' eomparatively small
<br />areas.
<br />30. Stream,gaging stations,-Run,off records are available at 14
<br />stations with periods of record varying from a few months to 21 years
<br />of complete record. Stream,gaging stations within the Purgatoire
<br />River Basin are listed in table No.6, appendix B.' Records were first
<br />obtained at Trinidad in 1897. The record at this station is continuous
<br />from 1920 to date, but prior to 1922, when an automatic g~e was in-
<br />stalled, the records are not in ,sufficient detail to obtain rehable esti-
<br />mates of flood peaks. The ma.ximum observed peak dischnrge ,of
<br />64,500 cubic feet per second in Purgatoire River occurred during the
<br />
<br />I Notprlntod..
<br />
|