PUB00094

• Year: 1998
• Title: Denver Basin and South Platte River Basin Technical Study: Technical Addendum 1 and 2
• Author: Special Water Committee
• Description: Technical addendums for the report
• Publications - Doc Type: Tech Report

Chapter 1: South Platte Basin Inventory

March 21.1998
Page 1-4

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

In conducting this Study, we obtained PACSM output data representing natural
flows and future flows for four of the five Study index gages (all except the Kersey
gage). We met with Denver staff to review the assumptions behind these data and
made adjustments were appropriate, as discussed below.

1.1.2 Natural Flows

For the purposes of this study, natural flows are defined as the surface water
flows that would occur without the influence of human activities,

1.1.2,1 South Platte at South Platte

For this gage location we relied on natural flow estimates previously developed
by Denver Water as part of their PACSM modeling effort. To develop natural flow
estimates for the South Platte at South Platte gage location, Denver adjusted historical
daily gage data for that location to correct for upstream reservoir operations and
evaporation losses, transbasin imports and South Park irrigation depletions, We have
reviewed Denver's estimates and compared them to previous estimates of natural flows
for this location, We believe that Denver's estimates for this location are the best
available data and are satisfactory for the purposes of this study, We have therefore
adopted Denver's natural flow estimates for this gage location without adjustment
Natural flows estimates for the South Platte at South Platte gage location are presented
in Table 1-1 and Figure 1-1,

1.1.2,2 South Platte Below Chatfield

For this gage location we once again relied on Denver's natural flow estimates
from PACSM. To develop natural flow estimates for this location, Denver used the
following general equation:

South Platte below Chatfield natural flow =
South Platte at South Platte natural flow +
Plum Creek at Louviers historical gage flow +
(allocated portion of natural stream gains between
South Platte at South Platte gage and South Platte at Littleton gage)

Denver quantified the natural stream gains between the South Platte and
Littleton gages via mass balance analysis using daily data for stream flows, diversions,
wastewater discharges, changes in reservoir storage and reservoir evaporation within
this reach. A portion of the total natural stream gain for this reach was then allocated to
the Chatfield gage location on the basis of relative drainage area,

Hydrosphere Resource Consu~.nts. 1002 Walnut Surte 200, Boulder, CO 80302