asp.net drop downlist value reset on button click within jquery dialog

I have a div , within which I have a button and an asp.net dropdownlist. I can change the value in the dropdownlist . But as soon as the button is clicked the value in the drop down list is again set to the default initial value. Is there a way I can solve this problem ? I do not want the dropdownlist to go back to its initial value.

aspx

<div id='one'>
     <asp:LinkButton ID="ConfigureAlerts" OnClick="btnConfigureAlerts_Click" runat="server">Configure Alerts</asp:LinkButton>
    </div>
    <div id="ViewModalPopupDiv2">
            <asp:UpdatePanel ID="UpdatePanel3" runat="server">
                <ContentTemplate>
                <asp:Panel ID="Panel2" runat="server" HorizontalAlign="left" ScrollBars="Auto">
                <asp:Button ID="btnGetLogs" runat="server" Text="SendAlerts" OnClick="btnSendAlertEmail_Click"/>
<asp:Label ID="Label2" runat="server" Text="Set The Alert Email Interval to every :" CssClass="label"
                                    ForeColor="Black"></asp:Label>&nbsp&nbsp&nbsp
           <asp:DropDownList ID="ddlTimeInterval" runat="server" >
                                    <asp:ListItem Text="15MIN" Value="15"></asp:ListItem>
                                    <asp:ListItem Text="30MIN" Value="30"></asp:ListItem>
                                    <asp:ListItem Text="1Hr" Value="60"></asp:ListItem>
                                    <asp:ListItem Text="2Hrs" Value="120"></asp:ListItem>
                                    <asp:ListItem Text="8Hrs" Value="480"></asp:ListItem>
                                    <asp:ListItem Text="24Hrs" Value="1440"></asp:ListItem>
                                    <asp:ListItem Text="48Hrs" Value="2880"></asp:ListItem>
                                </asp:DropDownList>
                                <br />                
</asp:Panel>
                </ContentTemplate>
            </asp:UpdatePanel>
        </div>

javascript

function ViewModelPopup2() {
        $("#ViewModalPopupDiv2").dialog({
                scrollable: true,
                width: 800,
                modal: true
            });
        }

ASPX.CS

protected void btnSendAlertEmail_Click(object sender, EventArgs e)
        {

            // Code to send email

        }

protected void btnConfigureAlerts_Click(object sender, EventArgs e)
        {

        ScriptManager.RegisterStartupScript
                       (this, this.GetType(), "callScriptFunction", "ViewModelPopup2();", true);
        }
    }