US Army Corps of Engineers

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2012 Changes to Stream Mitigation Procedures and Guidelines

Mike Moxey

USACE, Mobile District IRT Chair

May 10, 2012

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Draft 2012 Mobile District Stream SOP

Addresses Perennial, Intermittent and Ephemeral Streams

1. Field Identification Method

2. Functional Assessment

3. Commensurate Mitigation Strategy in Worksheets

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Stream Types Perennial Stream - A perennial stream has defined bed and bank (channel) features with flowing

water year-round during a typical year. The water table is located above the streambed for most of the year. Groundwater is the primary source of water for stream flow. Perennial streams support a diverse aquatic community of organisms year round and are typically the streams that support major fisheries.

  Intermittent Stream – An intermittent stream has defined bed and bank (channel) features with

seasonal flowing water, when ground water provides water for stream flow. During drier periods, an intermittent stream may not have flowing water. The biological community of an intermittent stream is composed of species that are aquatic during a part of their life history or move to perennial water sources.

  Ephemeral Stream – An ephemeral stream bed may or may not have well defined bank

(channel) features with flowing stormwater only during and for a short duration after precipitation events in a typical year. The streambed of an ephemeral stream is located above the water table (uplands) year-round and runoff is the primary source of water. Ephemeral streams are upland features that under normal circumstances do not contain aquatic communities.

Definitions synthesized from:

1) 2012 Nationwide permits, February 21, 2012 Federal Register and

2) the N.C. Division of Water Quality – Methodology for Identification of Intermittent and Perennial Streams and Their Origins and

3) July 2010 HGM Manual for the Functional Assessment of High-Gradient Ephemeral and Intermittent Headwater Streams in West Virginia and Eastern Kentucky.

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Intermittent Stream (Obvious?)

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Ephemeral Stream

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Stream Identification Protocols in

Mobile District

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Commensurate Mitigation for Ephemeral Streams

Less mitigation

More mitigation

For all streams, riparian buffer effects water temperature with shading and is a source of POC and DOC to downstream aquatic resources. Contribute to functional and ecological integrity of downstream aquatic resources

Ephemeral Streams: Dedicated upland collection and delivery system for hydrology, sediment, and organic material supply to downstream system.

Intermittent streams also provide aquatic insect (surface and hyporheic zone), aquatic habitat, and fisheries functions when flowing.

Perennial streams also provide consistent fisheries, aquatic insect, and aquatichabitat functions.

Ephemeral

Intermittent

Perennial

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HGM Functions

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Changes to Mobile District Stream SOP: Existing Condition

A. Geomorphologically Stable (Stable)

These streams exhibit reference condition pattern, profile and dimension. The channels show very little incision and little or no evidence of active erosion or unprotected banks (usually outside stream bends only), within the stream reach 80-100% of both banks are stable and contain vegetative surface protection or natural rock stability along the majority of the banks. Stable point bars and bankfull benches are present (when appropriate for the stream type). These channels are stable and have access to their original floodplain or fully developed bankfull benches. Correct sediment size and type for the stream type. If sediment deposition is present, it covers less than 10% of the stream bottom and is transient. Ephemeral streams have greater than 75% canopy coverage or a high quality riparian zone habitat.

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Proposed Changes to Stream SOP Adverse Impact Worksheet

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Proposed Changes to Stream SOP In-Stream Credit Worksheet

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Goal for Riparian Buffers

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Vs. No Riparian Buffers

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Proposed Changes to Stream SOP Riparian Buffer Calculations

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Continuing Challenges With Ephemeral Streams

Physical form and functions are dependent upon landform and normal rainfall events. How do we design appropriate projects if these have changed?

What are the criteria for prioritizing on-site versus off-site mitigation?

What is the standards and protocol for evaluating temporal and spatial success of ephemeral stream channel mitigation projects?

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Any Questions?

U.S. Army Corps of Engineers

Attention: Mike Moxey

109 St. Joseph Street

Mobile, AL 36601

Phone: 251-690-2658

Email: michael.b.moxey@usace.army.mil

Website: www.sam.usace.army.mil/rd/