how to copy 2dArray to another one

int[,] a1 = new int[4, 6];
a1[2, 3] = 4;
a1[3, 5] = 25;
int[,] a2 = new int[a1.GetUpperBound(0) + 1, a1.GetUpperBound(1) + 1];
Array.Copy(a1, a2, a1.Length);

public static int[,] copying2dArray(int[,] array, int rowLength, int clumnLength)
    {

        int[,]Copy = new int[rawLength, columnLenggth];
        for (int i = 0; i < rooms; i++)
        {
            for (int j = 0; j < timeSlots; j++)
            {
                Copy[i, j] = aray[i, j];
            }
        }
        return populationCopy;
    }