[Code of Federal Regulations]
[Title 40, Volume 24]
[Revised as of July 1, 2005]
From the U.S. Government Printing Office via GPO Access
[CITE: 40CFR230.25]

[Page 265-266]
 
                   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

[[Page 266]]

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.