[Code of Federal Regulations]
[Title 40, Volume 22]
[Revised as of July 1, 2003]
From the U.S. Government Printing Office via GPO Access
[CITE: 40CFR230.25]

[Page 263]
 
                   TITLE 40--PROTECTION OF ENVIRONMENT
 
         CHAPTER I--ENVIRONMENTAL PROTECTION AGENCY (CONTINUED)
 
PART 230--SECTION 404(b)(1) GUIDELINES FOR SPECIFICATION OF DISPOSAL SITES 
FOR DREDGED OR FILL MATERIAL--Table of Contents
 
Subpart C--Potential Impacts on Physical and Chemical Characteristics of 
                          the Aquatic Ecosystem
 
Sec. 230.25  Salinity gradients.

    (a) Salinity gradients form where salt water from the ocean meets 
and mixes with fresh water from land.
    (b) Possible loss of environmental characteristics and values: 
Obstructions which divert or restrict flow of either fresh or salt water 
may change existing salinity gradients. For example, partial blocking of 
the entrance to an estuary or river mouth that significantly restricts 
the movement of the salt water into and out of that area can effectively 
lower the volume of salt water available for mixing within that estuary. 
The downstream migration of the salinity gradient can occur, displacing 
the maximum sedimentation zone and requiring salinity-dependent aquatic 
biota to adjust to the new conditions, move to new locations if 
possible, or perish. In the freshwater zone, discharge operations in the 
upstream regions can have equally adverse impacts. A significant 
reduction in the volume of fresh water moving into an estuary below that 
which is considered normal can affect the location and type of mixing 
thereby changing the characteristic salinity patterns. The resulting 
changed circulation pattern can cause the upstream migration of the 
salinity gradient displacing the maximim sedimentation zone. This 
migration may affect those organisms that are adapted to freshwater 
environments. It may also affect municipal water supplies.
    Note: Possible actions to minimize adverse impacts regarding site 
characteristics can be found in subpart H.