FLOOD09697

• County: Statewide
• Community: Nationwide
• Basin: Statewide
• Title: Mathematical Modeling of a Sociological and Hydrologic Decision System
• Date: 6/1/1978
• Prepared By: Institute for Social Science Research on Natural Resources, Utah State Univ.
• Floodplain - Doc Type: Educational/Technical/Reference Information

NORMAL ANNUAL AND MAY-SEPTEMBER PRECIPITATION
1931-1960

T,
I
.

T.
,
.

T.
3
S.

R.IW. R.IE. R.2E
LEGEND
_ 20 _ bolines of Normal Annual fucipitaUon in Inches

. . . 10. .. bolines of Normal May-Seplember fucipitlllon in Inches

(Note ilollne Inle....ol <"..._1
Source: 1 :500,000 map, Slate of Utah, by U.S. Weather Burelu,
Salt Lake Cily, Utah, 1962.
Base Map: ] :250,000 Army Map Service. Salt Lake City Sheet,
196Jlimiledrevision

Figure 26. Figure showing the influence of the
Wasatch Front on precipitation patterns
(after Kaliser. 1973).

tUTes increase rates of water use by planls and deplete
water supplies stored in the soil from spring snow-
melt or summer rains. Cooling autumn temperatures
bring changes in the patterns of air movement and
alter precipitation characteristics. Leaves fall, and
evapotranspiration rales decrease markedly. Thus,
the changing seasons as characterized by air tempera-
tures have a significanl influence on a hydrologic
syslem.

Surface air lemperatures in the Salt Lake area
range from an average January temperature of280P
to a July average of 770F. The low and high tempera-
ture of record al Sail Lake City are -200F and IOsoF,
respeclively.

Because of the high intensity and short duration
of convective stonns, only a relatively small portion
of the lotal rainfall infIltrates at the point of incidence.
Thus, surface rWlOff rales usually are high, and flood-
ing is common. Because it tends to reduce infiltration
rales and speed surface runoff, urbanization usually
increases flood flows. These effects, coupled with the
greatly increased damage opportunities, make the flood

protection in urban areas a matter of prime concern
for municipal planners and engineers.

Drainage Conditions

Surface runoff from the study area flows to the
Jordan River in either natUTaI or man-made wal.er
COUTseS. The drainage patlern is slrongly influenced
by such man-made barriers as railroad and highway
embankments. In many cases, culverls do not have
adequate capacity, and ponds are formed. In other
cases, flows are conveyed along the embankments to
culverts at centrallocalions. Streets with their accom.
panying curbs and gutters also profoundly influence
drainage patterns. Irrigation channels and storm sew.
ers also affect surface drainage. Characleristics of Ihe
main natural drainage channels for Ih~ subzones of
FigUTe 2.2 are shown by Table 2.3.

Instrumentation

The basic hydrologic data network for the study
area consists of two precipitation stations and one
stream flow gage in the rural porlions (FigUTe 1.1),
and nine precipitation slations and eighl slream gages
in the UTbanizing portions (Figure 2.7). Three stream

...

~t73
~"

,.

. precipitation station
A stream gaging station

Figure 2 Z Hydrologic instrumentation and the Thies-
sen polygons for precipitation analysis
within the urbanizing portion of the study
area.

20