USACE CWMS - Santa Ana Watershed

The Corps Water Management System (CWMS) includes four interrelated models to assist with water management for the basin:
- GeoHMS (Geospatial Hydrologic Modeling Extension)
- ResSIM (Reservoir System Simulation)
- RAS (River Analysis System)
- FIA (Flood Impact Analysis)
The Santa Ana River Basin is located in Southern California and
has a drainage area totaling 2,460 square miles.. Of the total basin area, 2,255 square miles lie
upstream of Prado Dam, which is the primary flood risk management structure of the Santa Ana River.
The watershed spans mostly within the San Bernardino and Riverside Counties, and portions of Orange
and Los Angeles Counties.
Approximately 23 percent of the Santa Ana basin lies within the rugged San Gabriel and San Bernardino
Mountains, 9 percent within the San Jacinto Mountains, and 5 percent within the Santa Ana Mountains.
Most of the remaining area consists of lower-sloped valleys formed by a series of broad alluvial fan
surfaces which abut the base of the mountain front. Numerous low foothills rise above the alluvial fan
surfaces and include a range of hills north of the San Bernardino; the Crafton Hills east of Redlands; the
Jurupa Mountains north and west of Riverside; the Box Springs Mountains and the Badlands east of
Riverside; and the Chino and Peralta Hills northeast of Anaheim. In general, mountain ranges within the
basin are steep and sharply dissected. Maximum elevations in the Santa Ana basin reach 10,800 feet
NGVD at San Antonio Peak in the San Gabriel Mountains; 11,502 feet NGVD at San Gorgonio Mountain
in the San Bernardino Mountains; and 10,804 feet NGVD at Mount San Jacinto in the San Jacinto
Mountains. San Bernardino Mountains contain the headwaters of the Santa Ana River and two of its
principal tributaries, Bear and Mill Creeks. Lytle Creek, the largest tributary originating in the San Gabriel
Mountains, is in the northwest portion of the watershed. The San Jacinto River has its origin in the San
Jacinto Mountains southeast of Beaumont. The Santa Ana River has an average gradient of about 240
feet/mile in the mountains and about 20 feet/mile near Prado Dam. The average gradients of the principal
tributaries are approximately 700 feet/mile in the mountains and about 30 feet/mile in the valley areas.
The mountainous areas are expected to remain largely undeveloped during the entire project life. The
valley areas below Prado Dam are presently partially urbanized and are expected to approach complete
urbanization by the end of the project life.
The entire Santa Ana River Basin is underlain by a basement complex of crystalline metamorphic and
igneous rocks, which appear on the surface only in the most mountainous parts of the watershed. In the
foothills and valleys, the basement complex is overlain by a series of sandstones and shales.
Unconsolidated alluvial deposits range in depth from a few feet within the mountains to more than 1,000
feet on the alluvial fans in the valleys. The existence of several precipitous mountain scarps along the
upper boundaries of the watershed indicates that the area has been subjected to extensive folding and
faulting. The soils in the mountains, which are derived mainly from metamorphic and igneous rocks, are
shallow, poorly developed, and stony. On the lower slopes of the mountains and foothills, soils are mainly
loams and sandy loams, ranging from less than 1 foot to over 6 feet deep. In the valleys, where soils are
usually more than 6 feet deep, surface soils range from light, sandy alluvium to fine loams and silty clays
with heavier subsoils.
In general, the Santa Ana River Basin has a mild climate with warm, dry summers and cool, wet winters.
Both temperature and precipitation vary considerably with distance from the ocean, elevation, and
topography. At the city of Corona, about 26 miles from the ocean and 710 feet above sea level, the
average temperature is about 63 degrees Fahrenheit, with extremes of 22 degrees Fahrenheit and 118
degrees Fahrenheit recorded. At Squirrel Inn, located in the San Bernardino Mountains at an elevation of
5,700 feet NGVD, the average temperature is about 53 degrees Fahrenheit, with extremes of zero
degrees Fahrenheit and 97 degrees Fahrenheit recorded. Precipitation characteristically occurs in the
form of rainfall, although in the higher elevations some falls as snow. In general, the quantity of
precipitation increases with elevation. The 97-year mean seasonal precipitation for the basin, which
averages about 20 inches, varies from 10 inches south of the city of Riverside to about 45 inches in the
higher mountain areas. Nearly all precipitation occurs during the months of December through March.
Rainless periods of several months during the summer are common.

《流域水资源管理系统》（Corps Water Management System，简称 CWMS）集成了四个相互关联的模型，旨在协助对流域的水资源管理：
- 地理水文模型扩展（GeoHMS，Geospatial Hydrologic Modeling Extension）
- 水库系统仿真（ResSIM，Reservoir System Simulation）
- 河流分析系统（RAS，River Analysis System）
- 洪水影响分析（FIA，Flood Impact Analysis）
圣安娜河流域位于南加州，总面积达 2,460 平方英里。其中，上游区域（即普拉多大坝以上）面积为 2,255 平方英里，普拉多大坝是圣安娜河流域的主要洪水风险管理结构。流域主要跨越圣贝纳迪诺县和里弗赛德县，以及奥兰治县和洛杉矶县的部分地区。
约 23% 的圣安娜河流域位于崎岖的圣加布里埃尔山和圣贝纳迪诺山脉之中，9% 位于圣哈辛托山脉，5% 位于圣安娜山脉。大部分剩余区域由一系列宽阔的冲积扇表面形成的低缓山谷组成，这些表面紧邻山前地带。众多低矮的山丘矗立于冲积扇表面之上，包括位于圣贝纳迪诺山脉北部的山脉；雷德兰兹以东的克拉夫顿山丘；里弗赛德市北西部的朱鲁帕山脉；里弗赛德以东的博克斯普林斯山脉和不良地区；以及阿纳海姆东北部的奇诺和佩拉尔塔山丘。总的来说，流域内的山脉陡峭且切割深刻。圣安娜山脉的最高海拔在圣安东尼奥峰达到 10,800 英尺 NGVD；圣贝纳迪诺山脉的圣戈里戈尼奥山达到 11,502 英尺 NGVD；以及圣哈辛托山脉的圣哈辛托山达到 10,804 英尺 NGVD。圣贝纳迪诺山脉拥有圣安娜河及其两条主要支流——熊溪和米勒溪的发源地。来自圣加布里埃尔山脉的最大支流——利特尔溪位于流域的西北部。圣哈辛托河发源于位于比蒙特东南部的圣哈辛托山脉。圣安娜河在山脉中的平均坡度为约 240 英尺/英里，在普拉多大坝附近约为 20 英尺/英里。主要支流在山脉中的平均坡度约为 700 英尺/英里，在山谷区域约为 30 英尺/英里。
在整个项目生命周期内，山区预计将保持大部分未开发状态。普拉多大坝以下的山谷区域目前部分城市化，预计在项目结束时将达到完全城市化。
整个圣安娜河流域下伏于由结晶变质岩和火成岩组成的基底复杂结构，这些结构仅在流域最崎岖的山地部分露出地表。在山丘和山谷中，基底复杂结构被一系列砂岩和页岩覆盖。未固结的冲积沉积物厚度从山中的几英尺到山谷冲积扇上的超过 1,000 英尺不等。流域上边界附近存在数处险峻的山脊，表明该地区曾经历过广泛的褶皱和断层活动。山脉中的土壤主要来源于变质岩和火成岩，土壤浅薄、发育不良且多石。在山脉和山丘的较低斜坡上，土壤主要是壤土和沙壤土，厚度从不到 1 英尺到超过 6 英尺不等。在山谷中，土壤通常超过 6 英尺深，表层土壤从轻沙质冲积物到细壤土和粉砂质粘土，下层土壤较为密实。
总体而言，圣安娜河流域气候温和，夏季炎热干燥，冬季凉爽多雨。温度和降水随距离海洋、海拔和地形而有很大差异。在距离海洋约 26 英里、海拔 710 英尺的科罗纳市，平均气温约为 63 华氏度，记录到的极端气温为 22 华氏度和 118 华氏度。在位于海拔 5,700 英尺 NGVD 的圣贝纳迪诺山脉的松鼠旅馆，平均气温约为 53 华氏度，记录到的极端气温为零度和 97 华氏度。降水通常以雨的形式出现，尽管在较高海拔地区有时会以雪的形式出现。总体而言，降水量随海拔升高而增加。该流域 97 年平均季节降水约为 20 英寸，从河滨市以南的 10 英寸到较高山区的大约 45 英寸不等。几乎所有降水都发生在 12 月至 3 月之间。夏季几个月的无雨期很常见。