Make Bootstrap Dropdown Menu Go Only Downwards?

i have a little problem with my Bootstrap Select Box on the following Website As you might notice while scrolling the page up and down its disturbing the dropdown opens to both si

Solution 1:

Options can be passed via javascript

$('.selectpicker').selectpicker({
    dropupAuto: false
});

or

by HTML tag

<selectclass="selectpicker"data-dropup-auto="false"><option>1</option><option>2</option><option>3</option></select>