Ground Water Levels Presentation

• File Number: 8420.500
• Description: South Platte River Basin Task Force
• State: CO
• Basin: South Platte
• Water Division: 1
• Date: 7/16/2007
• Author: Robert A. Longenbaugh
• Title: Ground Water Levels Presentation
• Water Supply Pro - Doc Type: Report/Study

The South Platte River acts as a drain. As irrigation began in the last half
of the 19th century, water levels rose significantly in the alluvial aquifer and
the South Platte became a perennial stream. This allowed more surface
diversions to occur down valley. Since the late 1890's the South Platte
has become a gaining stream - groundwater from the aquifer flows into the
River. It is these return flows that satisfy the downstream water rights.
Historically upstream water rights have diverted runoff in the River and the
return flows provide the water for the next downstream right. That
explains how it is possible for surface ditches to divert over four million
acre feet when the outflow from the mountains is only 1.4 million acre feet.
The River is sti{I a gaining stream throughout much of its length.
For management of both surFace and ground water to obtain a maximum
supply for the use of all of Co{orado's citizens there is a need for good
reliable data upon which to make the management decisions. Data
needed should include:
1) A good network of observation wells to monitor the state of the
water stored in the aquifer. Some of these should be equipped
with continuous recorders.
2) Good records on the volume pumped and the volume diverted
from the river by canals.
3) Good stream gagging station data
4) Periodic gain and loss studies of the River to quantify the impact
of other infrastructure changes.
5) Data to evaluate how the recharge to the aquifer is changing
because of canal lining or increases in on farm irrigation
efficiencies
6) Data are needed to accurately calculate the volume and location
of non-beneficial consumptive use
7) A calibrated and verified linked ground and surface water model
will be needed to assist the managers in day-to-day decisions to
plan for the future.
II. OTHER NATURAL AND MAN MADE CHANGES ARE INFLUENCEING
RETURN FLOWS TO THE RiVER.
The decrease in return flows to the South Platte River are not all due to
well pumping. ^
Examples:
1) Lining of canals or use of pipelines decreases seepage losses.
3