LogController.cs

public class LogController : ApiController
{
    public log4net.Repository.Hierarchy.Hierarchy LogHierarchy
    {
        get
        {
            return (log4net.Repository.Hierarchy.Hierarchy)LogManager.GetRepository();
        }
    }

    // LogManager.GetRepository().LevelMap[logLevel]

    [HttpPost]
    public IHttpActionResult Level(string level)
    {    
        try
        {
                var log4netLogLevel = LogHierarchy.LevelMap[level] ?? log4net.Core.Level.All;

                LogHierarchy.Root.Level = log4netLogLevel;

                LogHierarchy.RaiseConfigurationChanged(EventArgs.Empty);
        }
        catch (Exception ex)
        {
            return InternalServerError(ex);
        }

        return Ok();
    }

    [HttpGet]
    public IHttpActionResult Level()
    {
        return Ok(LogHierarchy.Root.Level.ToString());
    }
}