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U.S. Army Corps of Engineers

ATTN” CECW-P(IP)

7701 Telegraph Road

Alexandria, Virginia 22315-3859

 

Introduction

 

 

The waterway known as Malibu Creek is located in Los Angeles and Ventura Counties in California. The creek serves as a significant ecological corridor between Santa Monica Bay and Malibu Lagoon, along with both riparian and coastal areas within the greater watershed. Malibu Creek holds tremendous value, ranging from recreation taking place at Malibu Creek State Park, to providing an essential habitat for threatened or endangered wildlife such as California steelhead. Southern California is highly urbanized and accommodates a dense population, which undoubtedly poses a threat to the health of any adjacent ecosystems. Additionally, man-made aquatic barriers such as Rindge Dam retain sediment from reaching coastal areas and prevent vulnerable aquatic species from accessing all parts of the watershed. As such, the United States Army Corps of Engineers (USACE) has determined that this highly biodiverse area merits an ecosystem restoration study in order to assess the ecological needs of this habitat and how they are to be met via the appropriate plan of action.

 

Comments

 

1.

According to page 16 of the IFR, Rindge Dam reached its capacity for trapping sediment transported downstream from storm events in the 1940s. The impounded sediment incrementally spills over the dam during storm events. However, on page 17, the IFR discussion presented that this level of sediment is not adequate for beach nourishment for the Malibu Lagoon and shoreline downstream of the dam. The IFR mentions that it could take from 20-100 years before pre-dam sediment transport levels are restored to the lower reaches of the Malibu Creek watershed. Since then, Rindge Dam is at maximum capacity for impounded sediment and the lagoon and shoreline are in dire need of sediment for beach nourishment, how can these issues be concurrently addressed?

 

2.

Table 4.2-1 claims that of the three proposed options, trucking sediment directly to affected areas presents the lowest adverse effects to natural resources and ties with the other mechanical transport alternatives in efficiency and performance.  The Locally Preferred Plan, Alternative 2b2 implements mechanical sediment transport and removal of the dam arch.  As stated on page 69 of the IFR, marshes and mudflats in the Malibu Creek watershed are important to the health of the lagoon.  These areas of the watershed are at risk of being impacted by rising sea levels unless provided elevation with sediment deposits so that they may move further inland.  Has USACE considered the immediate benefit of trucking sediment directly to these areas of concern?

 

3.

Most California steelhead populations are either endangered or threatened under the Federal Endangered Species Act. Steelhead rely on freshwater streams for reproduction and development, departing for the ocean later in life. The intrusion of saltwater into the lower reaches of the watershed as a result of rising sea levels will no doubt create uninhabitable conditions for young steelhead. It is crucial that this population is able to access a suitable habitat. Additionally, a Yale University study by Brown et al. 2012 concluded that fish ladders are generally an ineffective means of ensuring aquatic habitat connectivity.  In reference to section 4.1.5 of the IFR (Fishways), it is strongly encouraged that the USACE implements practices other than fish ladders for reintroducing steelhead into the upper areas of the Malibu Creek watershed.  Section 4.1.8 states that Malibu Creek habitat quality above Century Dam is good to excellent but not worth the cost relative to the increase in aquatic habitat connectivity before the following barrier: Malibu Dam. Instead of removing Century Dam, what practices could be used to make the barrier traversable for aquatic wildlife? If Rindge Dam might be altered so that fish can move past it to access upper parts of the Malibu Creek watershed, does it make sense to not use similar practices for other aquatic barriers in this watershed?

 

References

 

 

Brown, J. et al. (2012, December 11). Fish and hydropower on the U.S. Atlantic coast: failed fisheries policies from half‐way technologies. Society for Conservation Biology. https://conbio.onlinelibrary.wiley.com/doi/abs/10.1111/conl.12000

 

 

United States Army Corps of Engineers. (2020). Malibu Creek Ecosystem Restoration Study Final Integrated Feasibility Report (IFR) with Environmental Impact Statement/ Environmental Impact Report (EIS/EIR) Los Angeles and Ventura Counties. https://www.spl.usace.army.mil/Missions/Civil-Works/Projects-Studies/Malibu-Creek-Study/

 

Please direct all responses to these comments to the following email address: This email address is being protected from spambots. You need JavaScript enabled to view it.    



Sincerely, 

 

Matthew Coughlin - Associate in Maryland

Environmental Reviewer 

Environmental Review Inc.

1792 Rogers Avenue

San Jose, California  95112