Before us is an order which dismissed plaintiff’s complaint. The trial court correctly interpreted the law, and we sustain its judgment.
Maxine L. Mecham filed a complaint for divorce on July 6, 1973. Defendant husband, was served August 30, 1973. In the complaint, plaintiff sought temporary alimony and child support. A decree of divorce was entered March 15, 1974. The record does not indicate that plaintiff pursued her demand for temporary alimony or support. The decree provided:
The plaintiff is hereby ordered, adjudged and decreed to be denied any right whatsoever to alimony for the past the present or the future forevermore, as the right to alimony is affected by the marital relationship existing between the parties to this action. . . . '
. . . Both the plaintiff and defendant are hereby ordered to assume and pay any and all debts incurred by themselves respectfully (sic) since the filing of the divorce complaint in this matter and to hold the other party free from harm thereon.
The decree further ordered defendant to pay plaintiff $75 per month as child support for the parties’ minor child.
In August 1973, Maxine Mecham began receiving welfare payments from the Department of Social Services for both herself and the child at the rate of $162.00 per month. She continued receiving these payments through September 1974. The Department of Social Services filed a complaint, which was served on March 5, 1975, pleading for reimbursement for the welfare payments made to Maxine Mecham. The department’s claim was predicated on Section 78-45-9, U.C.A.1953, as amended 1975, which grants it the right to proceed on behalf of the obligee to enforce the right of support against the obligor.
The trial court dismissed the action without prejudice to plaintiff’s right to intervene in the divorce action, so the department might proceed to enforce any rights Maxine Mecham might have against Richard Mecham for nonpayment of the support ordered, and to the extent to which the state might be entitled under the divorce decree.
However, in regard to the right of reimbursement for the sums paid in the interim between the filing of the divorce complaint and the entry of the decree, the trial court ruled:
. . . There is a distinction to be drawn between the statutory ‘duty’ of support and the statutory proceedings under which the amount of that support is to be fixed. If not otherwise fixed as in a divorce decree or a similar judgment, the amount to be paid by an obligor may be determined either by court proceed*125ings under Chapter 45 [Title 78] or by administrative procedures under 45(b) [45b]. In either case the department may proceed on behalf of the obligee. But in neither case can the department proceed to get a judgment against one owing a duty of support for welfare handouts when there has been no prior determination of the amount of support to be paid, and particularly] where, as in the case before the court, there has been a decree of divorce previously entered fixing the amount of support and/or alimony to be paid.
The trial court in its ruling stated that in the decree of divorce entered on March 15, 1974, the court had ordered defendant to pay Maxine Mecham $75.00 per month child support and that he should pay no alimony. The trial court ruled the divorce decree fixed the amount to be paid under defendant’s duty of support, and no further proceedings are required or allowed to otherwise change that determination, except a petition to modify the divorce decree because of a change of circumstances. The trial court ruled that a complaint under Chapter 45 of Title 78 is not the proper procedure to modify a decree of divorce. We agree.
Under Chapter 45, Title 78, the duty of support of the obligor is to the obligee. The state department of Social Services has only the right to enforce the amount of support which is due the obligee from the obligor.1 The department may not unilaterally determine that amount and then enforce the right of reimbursement by an action under Chapter 45. Under Chapter 45, the district court determines the amount due for support, after considering the relevant factors, some of which are specified in Section 78-45-7.
As to reimbursement for the support furnished to Maxine Mecham, the department’s rights are derivative and no greater than Maxine’s rights. In her complaint, Maxine pleaded for temporary alimony. In the decree, she was denied past and present alimony; defendant’s duty of support was determined, and the matter is res judicata. The department cannot file a complaint one year after a court has determined the amount of support (in this case nothing), and demand reimbursement under Chapter 45. The same principle applies to the child support which accumulated prior to the date of the decree, March 15, 1974. Maxine had pleaded in her complaint for temporary child support; there was no provision made in the decree for any sum expended for the support of the child from August 1973 to March 15, 1974. Maxine also had a duty to support the child, Section 78 — 45—4. Under the decree, she was ordered to assume and pay any and all debts she had incurred since the filing of the complaint and to hold her husband harmless. Maxine did not seek in the decree any sum for reimbursement for the money she had expended for the support of the child, although she had put the matter in issue in her pleading. The rights of the department are derived through Maxine — the matter is res judicata.
WILKINS, and HALL, JJ., concur.. Sec. 78-45b-l et seq. was enacted in 1975 and went into effect May 13, 1975 and Sec. 78 — 45-9 was amended to its present form. At the time the department paid Maxine and the date the department filed its complaint, Sec. 78 — 45-9, provided: “The obligee may enforce his right of support against the obligor and the state department of [public welfare] may proceed on behalf of the obligee to enforce his right of support against the obligor. Whenever the state department of welfare furnishes support to an obligee, it has the same right as the obligee to whom the support was furnished, for the purpose of securing reimbursement and of obtaining continuing support. . . ”