ALP 16

DRAFT: Flow Release Test Plan
March 24th, 2011
1. Introduction
Reclamations Durango Area Office is planning a Basin Creek flow test for Basin Creek Improvements
downstream of Ridges Basin in May 2011. This memorandum was prepared by the Sedimentation and
River Hydraulics Group at Reclamations Technical Service Center in support of planning for this flow
event. The maximum acreage budgeted for this test flow is 5,000 acre -ft. Included below are the project
purpose, questions to be addressed, a proposed flow plan, measurement plan, and description of
instrumentation.
Two site visits occurred in support of this event: a site visit on November 3, 2010 and a second visit on
March 15, 2011. During the first site visit, sloughing riprap was discovered on the face of Drop Structures
10 and 12. This concern is being addressed prior to the May test flow release. Observations from the
November test flow release are presented in the November 3, 2010 Site Visit Memorandum. The
original plan called for testing in the fall when fish eggs are not present in flows. However vegetation
benefits from high flow testing can be realized by releases in the spring when air borne seeds for
cottonwood and willow are available for establishing new plants in the flood plain.
2. Purpose and Study Questions
Three goals were defined by the Animas- La Plata Construction Office in Durango for a First Fill Flow
Test. The goals are to learn more about the stability of the drop structures, the stability of the channel
and the travel times and delivery losses of Basin Creek from the dam outlet to the Animas River. Results
from the First Fill Flow Testing should help address questions from all three areas of investigation.
Questions to be addressed are:
the stability and performance of the drop structures;
• Are any features of the drop structures susceptible to erosion?
• How stable is the riprap on the face of the drop?
• When is flow conveyed over the top of the structure rather than interstitially?
• Is stilling basin performance reduced by the presence of established vegetation?
• Should vegetation be cleared from the drop structures before beginning flow testing?
• Is additional maintenance required on the drop structures before and /or after flow
testing?
the stability and performance of the channel;
• Can cattails be managed at outlet works, stilling basins and upstream of drop structures,
through peak flows without mechanical removal?
• Determine bank full flow at all locations (out -of -bank at 125 cfs ?)
• Which locations are susceptible to erosion and channel avulsions?
• Can stability of the channels be increased through flow testing and management to
enhance the establishment of riparian vegetation?