These armies cut and cleared whole patches of forest for breastworks in mere hours at times, built bridges in advance of retreats as well as assaults and had engineers in the rear doing it all day long for fallback positions, I thnk the army corp of engineers in the game is historical and would play a major role in this as well.
http://civilwarhome.com/engineers.htm
Engineers In The Civil War
When the war began, the Union had 2 engineer corps. The Corps of Topographical Engineers conducted explorations, surveys, and reconnaissance's of uncharted areas and sites for defenses, first under the command of Col. John J. Abert, then beginning Sept. 1861, under Col. Stephen H. Long. B for reasons of efficiency, the Corps of Engineers absorbed the topographical engineers in 1863. The Corps of Engineers' duties included planning and erecting defenses, construction and destroying roads and bridges, placing and removing obstruction, conducting topographical surveys during campaigns, reconnoitering enemy works, and preparing and distributing accurate maps. The wartime chiefs of engineers, Brig. Gens. Joseph G. Totten and Richard Delafield (who succeeded to command in 1864), attempted to perform these duties with an assortment of Regular Army and volunteer officers and men, and with hired civilians. The Confederacy established a Corps of Engineers commanded by 4 chief during the war: Brig. Gens. Josiah Gorgas and Danville Leadbetter, Col. Alfred L. Rives, and Maj. Gen. Jeremy F. Gilmer. Fortunately, the Confederate engineers obtained the services of trained officers who had resigned from the U.S. Army, but they lacked equipment and maps when the war began. Equipment was purchased from foreign countries, captured from the enemy, and manufactured in the South, but deficiencies continued throughout the war. Among other duties, engineer officers energetically prepared maps that were quickly distributed to the various army commands. The Confederacy also organized engineer troops and hired hundreds of civilians and slaves to work on fortifications, roads, and bridges. Both Union and Confederate armies were unable to or, at times, unwilling to furnish sufficient men and equipment to the corps to complete important tasks. In spite of deficiencies, the engineers performed valuable and diverse services, and many trained engineer officers--among them George G. Meade, P.G.T. Beauregard, Joseph E. Johnston, and Robert E. Lee--became worth commanders of troops. Wikipedia Civil War
Pontoon bridge across the James River, Virginia, 1864
The Army Corps of Engineers played a significant role in the American Civil War. Many of the men who would serve in the top leadership in this institution were West Point graduates, who rose to military fame and power during the Civil War. Some of these men were Union Generals George McClellan, Henry Halleck, George Meade, and Confederate generals Robert E. Lee, Joseph Johnston, and P.G.T. Beauregard.[5] The versatility of officers in the Army Corps of Engineers contributed to the success of numerous missions throughout the Civil War. They were responsible for building pontoon and railroad bridges, forts and batteries, the destruction of enemy supply lines, and the construction of roads.[5] The Union forces were not the only ones to employ the use of engineers throughout the war; and on 6 March 1861, once the South had seceded from the Union, among the different acts passed at the time, a provision was included that called for the creation of a Confederate Corps of Engineers.[10]
The progression of the war demonstrated the South's disadvantage in engineering expertise; of the initial 65 cadets who resigned from West Point to accept positions with the Confederate Army, only seven were placed in the Corps of Engineers.[10] To overcome this obstacle, the Confederate Congress passed legislation that gave a company of engineers to every division in the field; by 1865, they actually had more engineer officers serving in the field of action than the Union Army.[10] The Army Corps of Engineers served as a main function in making the war effort logistically feasible. One of the main projects for the Army Corps of Engineers was constructing railroads and bridges, which Union forces took advantage of because railroads and bridges provided access to resources and industry. One area where the Confederate engineers were able to outperform the Union Army was in the ability to build fortifications that were used both offensively and defensively along with trenches that made them harder to penetrate. This method of building trenches was known as the zigzag pattern.