The Riverside County Flood Control and Water Conservation District shall give the necessary assurances that the local cooperation required by the United States on the project adopted and authorized in Section 12749.3 shall be furnished by the district. The district shall execute the project in conjunction with the Secretary of Agriculture and may make such modifications and amendments to the project as may be necessary to execute it for the purposes of Chapters 1 (commencing with Section 12570) and 2 (commencing with Section 12639) of this part.