How do i set up multiple portfolios (each with its own defined set of images -) to display on the same page?

Generally speaking this should produce the structure you’re looking for. It’s 4 separate WP_query loops, and each loop pulls in posts from the category named.

 <div id="portfolio">

        <div class="col">
            <?php           
                $cat1 = new WP_query(array('category_name' => 'design'));

                if($cat1->have_posts()) :
                    while($cat1->have_posts()) : $cat1->the_post();
            ?>
            <div class="item">
                <?php
                     if(has_post_thumbnail())
                     {
                            the_post_thumbnail();
                     }
                ?>
            </div>
            <?php       
                  endwhile;
             endif;
            ?>
        </div>
        <!---------------------------------------------------------------->
        <div class="col">
            <?php           
                $cat2 = new WP_query(array('category_name' => 'development'));

                if($cat2->have_posts()) :
                    while($cat2->have_posts()) : $cat2->the_post();
            ?>
            <div class="item">
                <?php
                     if(has_post_thumbnail())
                     {
                            the_post_thumbnail();
                     }
                ?>
            </div>
            <?php       
                  endwhile;
             endif;
            ?>
        </div>
        <!---------------------------------------------------------------->
        <div class="col">
            <?php           
                $cat3 = new WP_query(array('category_name' => 'branding'));

                if($cat3->have_posts()) :
                    while($cat3->have_posts()) : $cat3->the_post();
            ?>
            <div class="item">
                <?php
                     if(has_post_thumbnail())
                     {
                            the_post_thumbnail();
                     }
                ?>
            </div>
            <?php       
                  endwhile;
             endif;
            ?>
        </div>
        <!---------------------------------------------------------------->
        <div class="col">
            <?php           
                $cat4 = new WP_query(array('category_name' => 'magazine'));

                if($cat4->have_posts()) :
                    while($cat4->have_posts()) : $cat4->the_post();
            ?>
            <div class="item">
                <?php
                     if(has_post_thumbnail())
                     {
                            the_post_thumbnail();
                     }
                ?>
            </div>
            <?php       
                  endwhile;
             endif;
            ?>
        </div>

 </div>